Transportation Research Record: Journal of the Transportation Research Board

Aspects of dust and dust control have been studied for many years in most countries with unsealed road networks. However, no comprehensive coordinated study to investigate the processes affecting the generation of road dust, road dust measurement, road dust prediction, acceptability criteria for dust, or the performance of dust palliatives has been undertaken. Over the past 6 years, the Council for Scientific and Industrial Research has been engaged in such a study. Although research has been undertaken on behalf of numerous parties, experimental designs have been coordinated in an attempt to develop guidelines for the responsible use of dust palliatives. Unfortunately, many of the experiments that have been undertaken by product manufacturers and road authorities over the years have been uncoordinated and poorly monitored, with minimal information being recorded or published. Many of these experiments have failed, with the product always being blamed, and this, together with poor marketing techniques used by suppliers, has led to skepticism by the roads industry toward the use of the products. Scientific research, following detailed experimental designs, funded by the product suppliers has resulted in the development of guidelines for the use of certain products. Studies have shown that, provided the products are used under appropriate circumstances, they can provide a cost-effective interim measure to improve the quality of life and preserve construction materials until such time as the road can be upgraded to a sealed surface. The holistic approach to dust and dust control research that has been followed is discussed here, a summary of the findings is described, and recommendations toward implementing a dust-control program are made.

Budget constraints for transportation projects is a growing problem at the federal, state, and local levels. At the same time, several changes have been affecting demands placed on the transportation systems, for example, population shifts, changes in travel patterns, and changes in economic activity. County and local governments are faced with increased demands on some portions of their road systems, and other portions have seen a drop in the level of use. As a result, these transportation agencies are facing tremendous challenges to maintain their extensive road networks and provide improvements when and where needed. Traditional funding sources are no longer adequate. There is a great need for counties to explore innovative methods to increase revenues or decrease costs or both. However, because of the nature of rural states (i.e., low population density and a limited tax base), methods used to supplement public funding of transportation projects in urban areas may not be applicable. Described are 4 innovative financing methods (e.g., rural improvement districts) and 14 cost reducing strategies (e.g., sharing equipment) used by local governments in eight rural states. County road officials identified these methods through a mail questionnaire and rated key criteria, such as ease of collection, to evaluate each method before implementing it. Rural improvement districts, special assessment districts, and the wheel tax were identified as innovative methods that are not widely used to raise revenues for a county road system. Advantages and disadvantages of each innovative financing method identified are discussed.

Nearly all structural layers in roads originate as geological materials. The geological origin and chemical and mineralogical composition of these rocks varies considerably and after natural weathering processes affect the fresh rock, a wide range of potential construction materials evolves. After noting that the performance of geological materials in roads is better predicted by an engineering geological classification than by a strictly geological classification, an engineering geological classification system was developed in southern Africa during the late 1960s. This classified materials on the basis of their weathering potential, and products related to their expected performance in roads and the characteristics of each group are discussed. It is shown from an investigation of the performance of a wide range of materials used in unsealed road wearing courses that the engineering geological classification of a material cannot be used to predict accurately its performance in unsealed roads. Factors including mineralogy, geological structure, stage of weathering, local hydrological conditions, and the prevailing and past climate all have a major influence on their performance. Laboratory-determined geotechnical test results are necessary for acceptable classification purposes. The variability of these materials after weathering, however, increases the risk of their use and makes selection more difficult. Mechanisms for selecting and treating appropriate materials for use in unsealed roads are suggested.

The total length of the Finnish minor road network is about 345 000 km (214,373 mi). The Finnish National Road Administration is responsible for some 65 000 km (40,389 mi) of minor roads, which are called public roads. The remaining 280 000 km (173,984 mi) are private roads that are constructed and maintained mainly by property owners who usually form cooperative societies that take care of this in practice. The role of raw wood haulage is significant, representing about three-fourths of the transported tons if mainly short-distance gravel transportation is excluded. Annual rehabilitation and maintenance funding needs were estimated to be at the level of 750 million to 800 million FIM by using a network management system. The available funds should be allocated to locations where improvements lead to the widest possible positive effects for freight transportation and settlement. For freight transportation this means that frost-damaged road sections should be eliminated from locations that have the widest effects on the utilization of wood resources. To promote development in rural communities funds should be allocated for access roads to communities where other prerequisites for development also exist. The interface between public and private roads needs to be reassessed. The concept of private roads is a very inexpensive and effective way of maintaining low-volume roads.

Gravel roads account for a large portion of the total 5.1 million km (3.2 million mi) of rural roads in the United States. These roads support the movement of farm families, rural residents, school buses, mail carriers, tourists, and agricultural commodities. In recent years, these roads have been affected by several trends. First, agricultural states are experiencing population shifts from farming areas to urbanized centers as farm sizes continue to grow, further reducing population densities and traffic levels. Second, some states such as North Dakota are experiencing a shortage in quality gravel supplies. Third, more rural road users perceive a lower level of service on gravel roads and demand better services, specifically more paved roads. Finally, the reduction in transportation budgets limits the number of gravel road kilometers that can be properly maintained. Several research efforts that examined alternative approaches to reduce gravel road maintenance costs are summarized here. These strategies may generally be classified into (a) modifying gravel road surface for high traffic roads (i.e., paving or using chemical additives), (b) reducing maintenance on gravel roads with lower traffic volumes, and (c) closing unneeded gravel roads. These options require careful economic and legal analysis before they would be implemented. The results of a case study that investigated the feasibility of paving gravel roads with various traffic levels and a brief overview of a survey of chemical soil additives in Colorado, Montana, North Dakota, South Dakota, Utah, and Wyoming are reported.

Presented is the low-volume roads economic decision model (RED), developed to improve the decision-making process for the development and maintenance of low-volume roads of key importance in Africa. The model performs an economic evaluation of road investment options by using the consumer surplus approach. It is customized to the characteristics of low-volume roads such as the high uncertainty of assessment of model inputs, particularly traffic and the condition of unpaved roads, the importance of travel times for model validation, and the need for a comprehensive analysis of generated traffic, and to clearly define all accrued benefits. RED computes benefits for normal, generated, and diverted traffic and takes into account changes in road length, condition, geometry, type, accidents, and days per year when the passage of vehicles is further disrupted by a highly deteriorated road condition. Users can add other benefits to the analysis, such as nonmotorized traffic, social services, and environmental effects, if computed separately. The model is presented on a series of Excel 5.0 workbooks that collect all user inputs, present the results efficiently, and perform sensitivity, switching values, and stochastic risk analyses. The model soon will be subject to empirical testing using data from selected countries.

Recently the Pacific Northwest Region of the U.S. Department of Agriculture Forest Service conducted laboratory tests evaluating the expected field performance of various additives on dense-graded aggregate. Additives used in the laboratory analysis included chlorides, clay, enzymes, lignin sulfonate, synthetic polymer emulsions, and tall oil emulsions. Laboratory analysis included indirect tensile strength and durability testing on AASHTO T 99 fabricated samples. Durability was evaluated after a number of wet-dry and freeze-thaw cycles. Other variables in the study included the amount of additive and the cure (temperature and time) before testing. Findings and observations include the following: (a) Untreated dense-graded aggregate provides little tensile strength in warm dry climates, (b) Chlorides, clay additives, enzymes, and sulfonate provide some tensile strength in warm dry climates. With increasing moisture contents they lose their tensile strength, (c) Once cured, synthetic polymer and tall oil emulsions provide significant tensile strength in warm dry climates. In wet climates these additives would tend to break down with increased exposure to moisture or freezing. (d) Increasing the percent residual (solids) of the synthetic polymer emulsions and tall oil emulsions increases the tensile strength and durability of the treated material, (e) Cure temperature has a dramatic impact on tall oil emulsions’ tensile strength and durability resistance. (f) The use of nontraditional additives can be cost-effective depending on the projects’ objective, the type of in-place material, and the cost of the additive.

India faces a very tough challenge to provide an adequate road network to its villages under serious constraints of funds. Present planning practices of rural roads mostly are based on ad hoc approaches, which leads to suboptimal utilization of funds. Presented is a user-friendly model for systematic planning of rural road networks that increases the efficiency of available resources for rural roads. The model provides an all-weather road connection from each village to nearby market centers and education centers at the least cost by generating an optimal rural road network. The model is computer based, which facilitates its effective application. It generates an optimal rural road network by using a heuristic approach that minimizes total transportation cost of the network. The model can be used effectively for preparation of master plans of rural roads. The tasks that can be performed by the model include (a) identifying the requirements of fresh road construction; (b) identifying the need for upgrade of an existing road network; (c) selecting appropriate design and construction standards; (d) identifying important missing bridges and missing links from an existing rural road network; and (e) identifying priority links for maintenance in an existing rural road network. Practical applications of the model demonstrate significant advantages over the prevailing practices of rural road planning in India.

Petroleum Development Oman undertook a study in 1996 to evaluate the use of a sulfonated petroleum product (SPP) as a base/subbase stabilizer and the performance of slurry seal and double sand seal in paving applications. Eight different road sections were constructed for a total length of 23.3 km. They constituted part of Marmul-Thumrait road project where the average traffic is about 150 vehicles per day. The objective was to improve the performance of graded roads and provide a low-cost base suitable for application of a thin bituminous surfacing. All eight sections were constructed with the standard subbase and base layers specified for roads in the Sultanate of Oman. However, major exceptions were as follows: Section 1, a slurry seal surface on normal resheeted base; Section 2, a slurry seal surface on SPP-stabilized base and subbase; Section 3A, unstabilized base and subbase (control section); Section 3B, SPP-stabilized base and subbase with a slushed finish carried out during construction; Section 4A, SPP-stabilized base and subbase with a slushed finish carried out a period of time after pavement construction; Section 4B, SPP-stabilized base and subbase; Section 5, a double sand seal surface on SPP-stabilized base and subbase; Section 6, a double sand seal surface on normal resheeted base. Road sections were monitored monthly for 6 months. The evaluation program included visual assessment of the surface, riding quality, dust generation, gravel loss, rutting, and in situ strength with a dynamic cone penetrometer. There were no differences in gravel loss, dust generation, strength values, or signs of distress between the stabilized and unstabilized sections. For the paved roads, the slurry seal section with SPP-stabilized base and subbase displayed the best performance in terms of less rutting and bleeding.

Experience in promoting suitable technologies and improving operational performance is drawn on to enable developing countries to make more effective use of local resources in the construction and maintenance of low-volume roads. Training and technology transfer projects require multidisciplinary consulting and advisory support, which may include courses and on-the-job training but may also require “twinning” and other linkages between institutions for a more substantial transfer of skills over a longer period. The process is illustrated by case studies from a range of national and international technical cooperation projects, including the global Management of Appropriate Road Technology research initiative and the World Road Association’s World Interchange Network. The cases are set within a framework of basic models of ways in which training and technology transfer can contribute to international construction industry development, which suggests an inverse relationship between project predictability and recipient autonomy. The analysis offers several general lessons for engineers involved in international technology transfer, including (a) the importance of assessing local administrative, social, cultural, and regulatory environments at the project design stage; (b) the need for an open-minded approach to the choice of technology; (c) the scope for working with and through the local private sector; (d) deciding on an appropriate mix of technical and management training; and (e) applying the principle of sustainability through recognition of recipient autonomy and maintained contact between provider and recipient institutions to build confidence through collaboration.

Most thin-surfaced unbound granular pavements are rehabilitated by overlaying with an unbound granular material and surfaced with a chip seal (thin-surfacing). The unbound granular overlay thickness is the difference between the total granular thickness required for future traffic and the granular thickness required for past traffic as determined from the design chart. However, where there are signs of shoving or other indications of a weak and degraded aggregate base layer then a smoothing treatment will not be adequate. For this situation the appropriate rehabilitation is either in situ stabilization (to improve the strength of the aggregate base material) or to cover with a minimum thickness of unbound granular material (determined from the thickness design chart by assuming the existing pavement acts as a subbase). This method of unbound granular overlay design has resulted in significant cost savings over the past 20 years in rehabilitation treatments for New Zealand roads, as the existing pavement has been fully utilized. In 1995 New Zealand adopted the Austroads (the Association of State, Territory and Federal Road and Traffic Authorities in Australia) procedures for pavement design. The Austroads procedures encourage the use of mechanistic procedures for pavement design. By using the same assumptions as the design chart method for determination of granular overlay depths, a mechanistic design procedure for rehabilitation treatments was developed. This method produces comparable results and has the advantage of being able to design a range of rehabilitation treatments.

During October 1996 a 10-km-long, double-lane, two-layer bituminous surface treatment (BST) was constructed near Bend, Oregon. The bottom BST layer consisted of an application of rapid setting high float emulsion (HFRS-2) followed by an application of 19- to 12.5-mm chips. The top layer consisted of various emulsions and 13- to 6.3-mm chips. Soon after construction up to 20 large commercial timber hauling trucks per day used the road during the wettest November and December in over 20 years. By the end of December 1996 most of the top layer of chips had disappeared, large numbers of potholes had developed, and the emulsion was not adhering to the bottom layer of chips. Failure resulted from interacting factors including a dust coating on the chips, an incompatibility of emulsion and chips, cold and wet weather, and a nearly impervious base course. The following lessons were learned from this project: (a) An adequate and accurate quality control and quality assurance plan should be in place before construction. (b) In wet environments, base courses under a BST should be free draining. (c) Either cool and humid construction weather or dust coatings on the aggregate may not lead to failure, but in concert they raise the potential for failure dramatically. (d) Not all emulsions are manufactured the same. An emulsion’s break and cure time may vary depending on the emulsion’s additives. (e) The asphalt emulsion and aggregate must be compatible with each other at conditions expected on the road surface.

Australia is a vast country with diverse environmental conditions ranging from mountainous to flat terrain, from large deserts to tropical areas with varying soil types, rainfall, and traffic conditions. The total road network in Australia is about 900 000 km, with more than 85 percent made up of local roads. This requirement places heavy demands on the development and maintenance of our road network for a sparse population of over 18 million and with limited resources. Local governments across Australia are in need of practical and understandable solutions to the many road transport problems they face. Coupled with this is the need to better manage road assets to gain maximum benefit from the limited road funding available. In late 1991 ARRB Transport Research Ltd. began an active technology transfer program aimed at helping the local road practitioners improve the performance of their road assets by making greater use of the latest developments, research findings, and provision of technology transfer services. Highlighted is how ARRB Transport Research is working with local government and other agencies responsible for local roads to put research, new developments, and services into the hands of practitioners so as to better manage local road assets. Addressed are the establishment of practitioners’ road needs, delivery of research to meet the specific needs of local roads, development of numerous technology transfer activities, and reported benefits of the activities undertaken.

To develop a new specification of material for surfacing unpaved roads, an experiment was conducted on 41 unpaved road sections located in five different physiographical regions in the state of Rio Grande do Sul, Brazil. The behavior of the sections under observation was analyzed qualitatively to evaluate the performance of the applied surfacing material. Because the traditional soil classifications (Highway Research Board and Unified Soil Classification System) are not suitable for classifying tropical soils, a new classification, namely MCT (miniature, compacted, tropical), developed in Brazil in 1981 was adopted as a basis for material selection. The behavior parameters observed were support, frictional resistance, and durability. The results obtained led to the specifications presented here, which were tested during a doctorate research program developed between 1991 and 1996 conducted by the first author and supervised by the second. It was concluded that the proposed specification based on the MCT classification system is more adequate than the ones previously used based on traditional classifications. The “binder content” of soils, a measure similar to that used for bituminous materials (asphalt binder content) is introduced to evaluate the agglomerating capacity of the fine fraction and, therefore, the material durability.

The roles of teams and technology transfer in enhancing safety on low-volume roads are addressed. Roadway safety is a multidisciplinary science involving several elements: (a) the three components of the roadway system—people, vehicle, and roadway; (b) the agencies and groups that plan, design, build, and use roads and promote roadway safety; and (c) the public health and safety communities that are concerned with injury prevention, response, treatment, and rehabilitation. Often the people working within these separate elements are characterized by interests, methods, and means limited by the boundaries, real or perceived, of their disciplines, organizations, and cultures. The application of technology transfer and teamwork enhances the efficacy of efforts to focus these elements on issues and problems related to roadway safety. Three broad topics are discussed. First, the importance of integrating the efforts of technical and nontechnical people and organizations through the development and management of multidisciplinary working groups and teams is explained. An associated topic is the conflict and ambiguity expected with expertise roles, boundary roles, and culture. Second, the importance of technology transfer in establishing and maintaining roadway systems used by motor vehicles, nonmotorized vehicles, and pedestrians and in educating and training engineers, engineering technicians, and the general population to design, build, maintain, and use roads safely is highlighted. Third, the importance of existing agencies in providing an organizational infrastructure that may either facilitate or hinder roadway safety planning and operations is described.

Macadam principles in pavement engineering were applied in South Africa up to around 1960. Mechanization and increased production requirements led to a decline in the use of macadam layers. More recently interest in macadam pavements in South Africa was renewed because of the labor-friendly construction methods. Much of the experience that had been available was lost as people retired, and new techniques of construction gave a new perspective. There is thus a need to provide guidance to new entrants to the industry and capture the experience that was common knowledge several decades ago. The aim of this report is to present a guideline document for construction of appropriate and economic macadam pavements based on extensive South African research coupled with vast experience in the construction of these layers. Guidance on appropriate use of the different variants of macadam layers, the material properties, the structural design process and catalogue, functional design considerations, and construction practice is provided. It was found that under the current socioeconomic upliftment program macadam principles provide an appropriate and cost-effective solution to paving urban streets.

Botswana is characterized by a number of features, including its vast size, small and spatially dispersed population, scarcity of conventional road building materials, near absence of surface water, and climatic extremes, which combine to pose a major challenge to economic road construction. This has dictated a need for developing innovative approaches to road technology in circumstances in which conventional approaches often are prohibitively costly and inappropriate for direct application to local conditions. Presented are several innovative, cost-saving approaches to road technology in Botswana that have been developed through several decades of research with the aim of optimizing the use of locally available resources. The applicability of these techniques in similar environments with a semiarid climate also is discussed and the need for caution when using standard specifications in areas such as Botswana is highlighted.

Pavement condition data collected from several sections of village roads were correlated with analytical structural response of pavements for developing a performance-based rutting criterion. Laboratory tests were carried out to obtain the design parameters, and a computer program was used for layered elastic analysis of pavement structure. Charts were prepared for design of village road pavements with a reliability level of 50 percent.

Summarized are problems associated with low-volume road (LVR) passive grade crossings, low-cost innovative devices that have been developed and tested to improve safety, policies, and programs that have been developed and promoted in the United States to enhance safety at LVR grade crossings, particularly at night. On the basis of safety studies and years of experience, conclusions and recommendations are presented to reduce drivers’ risk at the typical passive, rail-highway grade crossing found on LVRs. Stressed are the two keys to reducing risk at LVR, passive grade crossings: provide adequate sight distance and make the crossing and warning devices conspicuous, particularly at night.

Design and evaluation methodologies for low-volume rural roads have traditionally followed an agricultural focus, with an understanding that improved transport, by lowering transport costs, supports economic development through expanding exports and local incomes. More recently, the role of low-volume roads as a crucial complementary input to other activities has been recognized, especially the delivery of essential health and educational services, exchange of information, and basic social interactions. However, limited analytical work has been done to ensure that these benefits are systematically incorporated in the planning and evaluation of transport projects, and experience suggests that the current emphasis of design and evaluation on agricultural benefits can lead to inappropriate priorities and design standards, inasmuch as these are still typically guided by trading off infrastructure life-cycle costs (construction and maintenance) against motorized user savings (vehicle operating costs) and/or increased net income/value-added. There is a need to be more discerning in the application of existing methodologies, as well as to systematically incorporate the socioeconomic role of rural transport infrastructure (including poverty alleviation) into prioritizing improvements. Key to this analysis is the proposition that appropriate design standards need to balance the transport requirements of core economic and social activities with the impact of geography (geology, topography, and climate) on construction and maintenance costs. By taking into account the broader range of impact on local users, the proposed approach encompasses a wide array of options for providing minimum-cost, reliable infrastructure for both motorized and nonmotorized transport.

The need of local road managers to have a readily accessible reference guide for identifying deficiencies and improving safety on low-volume roads has prompted the development of a field guide for unpaved rural roads. Technical resources are available to evaluate the various aspects of a low-volume road. However, the resources are in numerous publications and not in a single, easy-to-use document. The concept of the field guide is to provide a single reference to assist rural road managers in making on-site evaluations of specific roadway deficiencies. Critical safety issues and unpaved rural road responsibilities vary throughout the United States. A national focus group was used to recognize this variability. A modified Delphi survey procedure was used to facilitate focus group input and review the project. The Wyoming Technology Transfer Center, in cooperation with the FHWA Local Technical Assistance Program, was responsible for development of the guide. Reviewed are the steps and considerations taken in the development of the guide. Developmental techniques, such as input from a national focus group of transportation professionals, were used to successfully complete this project. The methodologies used to develop this guide are applicable and potentially useful for completing other transportation projects worldwide.

The principal function of low-volume roads is to provide access to land uses adjacent to the road. The roads are important to industry for hauling raw materials and to local residents. Low-volume roads often intersect railroads, creating a grade crossing. This creates the potential for conflicts between modes and introduces delays for motorists when long trains occupy a crossing. These conflicts can reach unacceptable levels. Presented is a case study of one such situation. The George’s Creek area in Maryland is a significant producer of bituminous coal. A local coal operator wanted to ship coal via train to the port of Baltimore. Clearly, this would be a boost to the local economy. A rail line already served the area; however, there were no coal-loading facilities. The quantity of coal produced did not justify construction of such facilities. Thus it was decided to load the train by using mobile equipment. This required the train to block a low-volume road grade crossing for significant periods on a quarterly basis. Residents were concerned about access to their homes, emergency vehicle access, and grade crossing safety. Through communication, coordination, and cooperation among the mine operator, the railroad, and the local jurisdiction, a plan was developed wherein the mine was able to ship its coal by rail and local residents had safe access to their homes and emergency vehicle service. Implementation of the solution is detailed. Critical issues are identified and their resolution discussed. Lessons learned and suggestions for other locations facing similar problems are included.

The Federal Highway Administration’s Eastern Federal Lands Highway Division has been actively involved over the past 10 years with the development of a process to maintain better control of its design project schedules. Three initiatives were undertaken during this time period. The first initiative involved a change in structural organization by establishing a strong project management concept from a project’s inception to its construction contract award. The second initiative recognized early on that a well-scheduled project eliminates many of the problems encountered during the design process. The resulting scheduling resource system became a valuable tool for the project managers. In the third initiative, a team developed a road map of the design process to better serve the division’s customers. After 10 years, customer satisfaction is improving, project schedules are under better control, and improvements to the design process have resulted in timely and cost-efficient projects.

The Euroregional VIKING program includes several projects that have potential as intelligent low-volume road applications. In Finland, traffic volumes are on average very low and therefore the telematic applications often are designed to fit into low-volume traffic conditions as well. Some relevant projects are introduced. The projects include applications such as weather-controlled variable message signs and speed limits, local ferry traffic management, animal detection and warning system, cross-border data exchange in rural areas, and some ideas for the future such as managing the forest harvest traffic and low-cost road weather monitoring. Some of the experiences gained are encouraging but a lot of research needs to be done in future years. Although the applications described are evaluated as potential low-volume road solutions, many other applications may become available as the real prices of telematic equipment and systems fall over time. Recent estimates of the fall of real prices suggest that prices may decrease significantly, perhaps within 1 decade.

Subgrade soil strength and/or stiffness are major factors in the design and performance of pavements, particularly low-volume pavements. A practical method of realistically estimating in situ moisture content significantly improves the determination of the appropriate resilient modulus to be used for pavement design. Because of the variability in soil properties and soil behavior under repeated traffic loads, environmental factors, geometric factors, and site conditions, and because of the complexity of moisture movement in soils, the prediction of subgrade moisture content has been unreliable and complicated. In a study of subgrade moisture changes with time, temperature, precipitation, and depth at 18 sites across Arkansas, five general trends in subgrade moisture variation are identified. In addition, upper and lower equilibrium limits for subgrade moisture contents are estimated. These equilibrium values are independent of environmental factors and are solely dependent on soil properties and site conditions. Regression equations to predict upper and lower equilibrium values from soil properties are developed. It is shown that reasonable predictions of in situ moisture content may be developed, given the range of subgrade moisture content variation for a given soil type and the trends of moisture variation with temperature, precipitation, and depth. In addition, guidelines and issues to be considered when establishing a subgrade moisture content monitoring program are given. The information presented could provide agencies with responsibility for lowvolume roads valuable tools for obtaining reasonable estimates of subgrade moisture conditions without the need for extensive (and expensive) soil sampling and testing programs.

Road accident statistics from the Indonesian Traffic Police Headquarters for the last decade show that there have been 10,000 fatalities on average per year. This situation has become a serious national issue. Since 1989 the Overseas Unit of Transport Research Laboratory has been involved in a collaborative research study on road safety with the Institute of Road Engineering in Bandung, using the Microcomputer Accident Analysis Package (MAAP). A pilot study to implement the MAAP system was set up in four regions. The characteristics of road accidents on selected low-volume roads are described and processes for identifying contributory factors at hazardous locations are introduced.

Throughout the world, expansive soils are known to cause damage to light structures, such as residential dwellings, road pavements, and airfields. In Australia, moderate to highly expansive soils cover more than half the state of Victoria and produce significant maintenance problems to the state’s road network. Vertical moisture barriers have been used successfully in many cases across the United States to control movements generated from expansive soil subgrades. Field trials using moisture barriers have also been conducted successfully in Victoria, Australia. However, due to their expense, the treatment of using vertical moisture barriers has usually only been reserved for major highways. A review of current vertical moisture barrier construction methods in the United States is made, and a new construction method developed in Victoria that provides an effective and economical barrier is reported. This method will enable the application of vertical moisture barriers to be more attractive for sealed low-volume roads. A successful field trial of this construction method has been carried out at Dooen, in northwest Victoria, and has since been applied to several other projects in Victoria and South Australia.

Low-volume roads comprise a significant portion of the rural roadway network. Because of documented higher crash frequencies and more severe injuries on such roads, it is necessary to further examine causal factors of these crashes and to determine if crash characteristics follow the patterns of other highways. The quasi-induced exposure technique is used to analyze the relationship of driver, roadway, and environmental factors involved in crashes on low-volume roads. Crashes from Kentucky and North Carolina for 1993–1995 are used. The results show that (a) low-volume roads present similar crash trends as those observed on other roads; (b) drivers under the age of 25 and drivers over the age of 65 have higher crash propensities than middle-aged drivers; (c) female drivers are safer on average than male drivers; (d) young drivers (under the age of 25) experience more single-vehicle crashes and drivers over 65 are more likely to be involved in two-vehicle crashes; (e) drivers of older vehicles have higher two-vehicle crash propensities on low-volume roads than drivers of newer vehicles; (f) in single-vehicle crashes, drivers of older vehicles are more likely to have a serious injury than drivers of newer vehicles; and (g) large trucks have the highest two-vehicle crash propensity on low-volume roads, followed by sedans, pick-up trucks, vans, and station wagons.

Today’s geosynthetic products have many useful, creative, and cost-effective applications for rural, low-volume roads. In the management of almost a half-million km (quarter-million mi) of low-volume roads, the U.S. Department of Agriculture, Forest Service (USFS), has developed and adopted many uses for geosynthetics. An overview is presented of many of those uses and their advantages. The USFS gained much of its experience and practice with geosynthetics while constructing a wide variety of Mechanically Stabilized Earth (MSE) retaining walls, including geotextile, timber, modular-block, and tire-faced structures, and reinforced soil slopes. More recently, the USFS has used geosynthetics for MSE bridge abutments and Deep Patch road-shoulder reinforcement. Other typical geosynthetic applications include filtration, drainage, subgrade reinforcement, and erosion control.

With limited resources and increasing exposure to tort liability, local rural road agencies face the dilemma of how to maximize improvements to their road system. For unpaved rural roads the problem is particularly acute. Many of these unpaved rural roads worldwide have geometric deficiencies that do not conform with recognized standards and guidelines. In many instances, roadway improvements are not being completed because of the inability to fund improvements to meet these standards and guidelines. Incremental improvements for unpaved rural roads is potentially an important tool for local agencies. The goal is at least to meet minimum guidelines and standards by continuing to implement an incremental program. Reported here are the results of a project that used a national U.S. focus group to provide input into the acceptability of the concept and use of incremental safety improvements on unpaved rural roads. The investigation targeted horizontal curvature as a site deficiency. The focus group was used to identify if and what incremental improvements should be considered. The results demonstrated the need for functional subclassifications of rural unpaved roads, with incremental decisions made that address the unique operational differences. Incremental improvements, when properly considered, are recommended as an acceptable method to increase safety on unpaved rural roads and to minimize liability.

One of the challenges of South African civil engineers is to develop techniques for infrastructure provision appropriate to local conditions and suitable for creating employment. Local technology, consisting of welded plastic cells known as Hyson-Cells, is identified as a potential solution. After tensioning the cells, coarse aggregate is placed and compacted, after which a sand-cement grout is vibrated into the voids in the coarse aggregate. Alternatively, ready-mixed concrete can be used. The design catalogue for geocell pavements for low-volume roads is presented, and the suitability of the catalogue is demonstrated by evaluating streets that had been in service for more than 5 years. The catalogue of pavement structures was developed from the results of a laboratory study and field trials. An evaluation of eight road projects that had been in service for more than 5 years supported the structural design but also showed that construction control was important to ensure good performance. An economic analysis demonstrated that it was competitive with other pavement types normally used on access streets.

A prototype safety improvement program (SIP) developed specifically for unpaved roads is presented. The combination of high mileage, low traffic volume, and limited budgets makes it difficult for local agencies to adopt traditional SIPs. The presented SIP for unpaved roads is economically and procedurally appropriate for local road agencies. It provides a systematic means of prioritizing road sections for safety analysis and identifying safety improvement needs. One of the many unique features of the program is its “partnering” approach of involving public road users in the safety improvement process. Results of case studies that validate the procedure are included.

To address internal inefficiency and accountability issues, a number of Latin American countries have moved decisively and successfully over the last decade from force-account (direct labor) to contract maintenance. Also, there has been considerable progress in the region in transferring to the private sector, through concessions, the responsibility for improving, maintaining, and operating high-traffic-volume roads, the cost of which is recovered from tolls. Argentina, Brazil, and Chile are among the most advanced countries in this respect. More recently, some countries—particularly Argentina—have switched from the traditional quantities and unit price–based short-term maintenance contracts to long-term performance-type or results-based contracts. The new approach encompasses either routine maintenance activities alone or integrated contracts involving both the rehabilitation and routine maintenance of road networks. The latter form, the so-called CREMA system (Contrato de Recu-peración y Mantenimiento), is now being implemented in Argentina and covers approximately 12 000 km (i.e., about 40 percent of the national paved road network). Such contracts comprise the rehabilitation and subsequent maintenance over a 5-year period of 200-km- to 300-km-long subnetworks. A framework for extending the CREMA concept to low-volume roads is presented. The means by which this newly developed system could be extended to cover both the paving and future maintenance of low-volume roads is explained. Reasons are analyzed as to why this type of contract, which extends the contractor’s share of responsibility over a relatively long period of time, would be well suited to the specific design and construction features of low-cost, low-volume paved roads—in particular, in the risks related to uncertain traffic projections and in the use of local or nontraditional materials in thin pavement structures. Finally, issues related to the use of the CREMA system—especially the need to prepare adequate contract bidding documents, conduct proper bid proposal evaluations, and monitor contractor’s performance during the rehabilitation/paving and maintenance phases—are explored.

The need for lightweight, low-maintenance, easily constructed bridges for remote locations has existed for a long time. The backcountry of forests and parks throughout the United States is made accessible by trail systems that often encounter streams, rivers, gorges, and other features that must be spanned. Because of their remote locations, conventional approaches to spanning these barriers often are impractical. The Eastern Federal Lands Highway Division of FHWA, in conjunction with the United States Forest Service and with assistance from E.T. Techtonics, designed, tested, and constructed a pedestrian trail bridge 13.9 m (45.5 ft) long made of fiber reinforced polymer (FRP) composite members. Development of design procedures for this type of bridge is presented. The initial load testing results used to evaluate the analysis and design of the structure are presented and future construction plans for this bridge are mentioned. Attractive characteristics of FRP composites for construction of pedestrian trail bridges and shortcomings are illustrated. Further testing and research of the Falls Creek Trail bridge are ongoing and further testing and research of FRP composites also are needed. Advances in the understanding of currently available materials, as well as advances in the materials themselves, likely will affect structural design methods and procedures in the future. However, on the basis of available data, FRP composites appear to be well suited to meeting the need for backcountry trail bridges.

In India there are 0.6 million human settlements scattered all over the country. Forty-eight percent of these villages are connected with all-weather roads and the remaining 52 percent of these villages are yet to be connected with all-weather, black-topped roads. The prevailing construction methodologies that use mechanized implements do not suit the construction of low-volume roads in India due to the high cost of machinery and unavailability of skilled labor and technicians. In view of the above, the present methods of low-volume road construction and maintenance are largely labor-based. These methods are slow and often result in substandard quality of construction. Therefore, it is considered essential to adopt an appropriate man-machine combination. Such an approach will be necessary in the future to improve the standards of construction required for low-volume road infrastructure development and also to meet the accelerated pace of rural developmental activities. Cultivation and farming are the main activities in the villages leading to the availability of farming tractors and other related implements. Since tractors are increasingly available in large numbers in rural areas, it is considered most appropriate to make use of various agricultural implements towed by tractors for the different road construction operations. A survey was made of the existing agricultural implements suitable for carrying out the various road construction operations. Based on results of this study, different farming implements were used for various road construction activities on demonstration projects. The data obtained from these projects were analyzed to determine the technical and economic feasibility of labor-intensive and tractor-towed equipment construction techniques. An economic evaluation of these low-cost road construction techniques was performed to identify relative cost factors. Different low-cost agricultural implements and their possible use in various road construction operations are highlighted. Based on these studies, it is evident that the deployment of tractor-based techniques would result in substantial economy with the added benefit of better-finished quality of work and considerable time-saving in projects.

Numerous road construction projects in developing countries have aimed to provide low-cost roads. A major component of these road networks is the structures required to cross streams and rivers. On these projects little attention has been paid to the use of local resources and indigenous skills such as masonry, brick, or manufactured blocks for the construction of highway structures instead of reinforced concrete. A wealth of information is available to designers of highway structures in high-income countries, primarily on the design of large steel and reinforced concrete structures. However, these design guides and textbooks do not address the design of simple water crossings such as drifts, vented fords, or small bridges. There is a clear need for a design manual that provides information and guidelines for highway engineers who are designing structures on low-cost roads in developing countries with limited resources. The findings of desk and field studies for the preparation of a manual for road engineers, technicians, and supervisors in developing countries are discussed. The problems typically encountered in the design, construction, and subsequent use of highway structures are highlighted, and how the manual addresses these problems is discussed.

A quick and simple method of bridge substructure construction using geosynthetic reinforced soil (GRS) is illustrated. GRS is used to build abutments and pier foundations for simple bridges. It is a refinement of existing reinforced soil technology used during the last 20 years. The interaction of a closely spaced geosynthetic reinforced soil system and the reasons why conventional design methods are not appropriate for these closely spaced systems are explained. This method is not recommended for all bridge building assignments; for example, it is not suitable for construction of permanent bridges in scour zones. The technique is ideal for remote locations, inaccessible to use of concrete and other traditional materials. A generic style of GRS construction is explained to ensure performance and internal stability. Construction is rapid with conventional equipment. The materials are common, inexpensive, and generally available. An overview of recent full-scale research is provided. The results of two full-scale prototype tests are presented to demonstrate performance and limitations and to confirm the design of such systems. A case history is presented that shows the versatility of the technology in a bridge support application. A procedure for prestraining or preloading the reinforced soil to enhance performance is provided. For bridge support applications, preloading of the GRS has the benefit of limiting postconstruction creep settlement. Preloading also proof-tests the structure and verifies the quality of construction. Additional sketches are included to show its potential for common applications. A brief discussion about design considerations to limit potential problems is offered.

A case study in which the researchers developed a prototype low-volume roads pavement management system (PMS) using a geographic information system (GIS) platform for Fountain Hills, Arizona, is described. The approach used and the problems faced are discussed. The first stage of the study entailed the collection of all information available from the city. City engineers provided a database with inventory and condition data, and an AutoCAD map of the city streets. The research team then evaluated several software packages. They selected the Road Surface Management System (RSMS) package developed at Arizona State University for the PMS portion. This program was developed to help local Arizona agencies systematically manage low-volume road and street pavements. The researchers evaluated two GIS packages for the study, based on the software’s capabilities and the city’s needs. They selected Maplnfo because it was less expensive and easier to learn. A menu-driven MapInfo application that runs the RSMS software, imports the pavement maintenance and rehabilitation program, and interactively prepares and displays colored maps with the analysis results was finally prepared. The combination of RSMS and MapInfo significantly reduced the effort required to develop the prototype system. It allowed the development and implementation of a GIS-PMS for the city, based on the existing digital data. City engineers were very impressed with the prototype system’s capabilities.

The highway maintenance scene in the United Kingdom is presented with respect chiefly to the minor (low-volume) road network. A 10-year study of the causes, consequences, and resulting maintenance options is presented based on observations in five highway authorities, at research sites of 100-m length at the worst end of the condition range. Edge- and non-edge-supported roads are featured, with or without positive and natural drainage. A pavement condition index (PCI) was developed comprising structural, surface, and edge indexes from manual surveys. Some correlation was achieved between PCI and profile from machine-based surveys. The concept of a time-independent relationship between rate of change in a number of condition indicators and absolute condition is advanced. Deterioration rates for eight conditions, as well as their variation in relation to causal factor “pairings” and between lost and remaining sites, are included. Some comparisons are made with the annual National Road Maintenance Conditions Survey of all road categories in the range of conditions found in practice.

Many unsealed roads carry relatively high traffic, which results in excessive maintenance requirements and costs. Sealing of these roads with a bituminous surfacing is typically cost-effective if minimal upgrading of the existing road needs to be done. An extensive evaluation of more than 50 roads that were constructed with base course materials of marginal quality, many with only a single layer of material over the subgrade, was carried out. Detailed evaluations of the in situ and laboratory properties as well as the performance of the roads indicated that good drainage and construction quality are the primary requisites for successful sealed low-volume roads. Provided these two criteria are met, current material standards and pavement designs can be significantly relaxed. The use of these light pavement structures results in significant environmental benefits compared with the construction of traditional pavement structures through conservation of higher quality materials, reduced energy usage through less haulage, and elimination of gravel loss and dust emission from the roads.

After more than 35 years of construction, the Austrian rural road network is almost completed. The construction of new roads will decrease within the next decade due to finalization of the development plans. Thus, the maintenance of the rural road network has been the major task for the last 10 years, and will continue to be important. An overview of the organization of the maintenance plans in the different provinces and of the financing is provided. As no federal funds are available for maintenance costs—unlike the case with new construction—only small contributions from provinces are possible, while the road owners and communities cover the majority of costs. This requires the most cost-effective maintenance methods and a lean organization for performing maintenance, like district or province maintenance associations. Research for the Federal Ministry of Agriculture and Forestry has provided a practical model for the systematic maintenance of rural roads. Thus, a technical basis for systematic pavement management for rural roads is already available, including all steps for inventory, condition rating, maintenance-method choice, and prioritization.

The exploitation of aggregates and soils for highway construction has a considerable impact on the economy and the environment and it is important that utilization of these materials is cost-effective. Obtaining and maintaining good records is costly and requires professional expertise. With modern computer technology it is possible to store information systematically and compactly. If quarry information is available in one central locality, better planning of road construction and maintenance and better management of materials resources can be realized. The research undertaken to create a materials information system in Indonesia is described. A pilot system was designed and tested in the province of West Java and comprehensive data collected from about 800 quarry sites. The Indonesian Directorate General of Highways, encouraged by the results of the pilot study, decided to introduce the system to all 27 provinces of Indonesia. Training courses were held to teach good practice and were successful because of improvements in the quality and quantity of data provided, but there is still scope to improve the utilization of the system by potential users. With accurate data the system is an improvement on the status quo. The system is simple to use, can be updated when necessary, and provides the basic information required by highway engineers. It is transferable to other countries in transition with minimal alteration. The data can be used in conjunction with terrain classification and Geographic Information Systems packages (such as MapInfo) to indicate potential new material sources.

A practical methodology for prioritizing road works on low-volume and very low-volume roads in the rural areas of developing countries is described. The methodology is based on a system for estimating future traffic on improved roads on the basis of readily available data. Moreover, the method accommodates the need to consider the opening of roads that may be currently impassable to motor traffic. The procedure is simple and transparent, and therefore it is well suited to implementation at the district level. It allows for certain basic parameters, such as minimum thresholds for viability of investments, to be set by decision makers, thereby permitting and defining the role of politicians in the process.

The results of a highway experiment, constructed in May 1978 in northern Belize, designed to investigate the suitability of locally occurring calcareous materials, known as marls, for road bases are discussed. The marls comprise high-purity carbonate materials containing mainly siltsized particles and fall outside the grading, plasticity, and strength specifications normally required for road bases. Three marls, each with slightly different characteristics, were substituted as road base for crushed stone. One of the marls was also stabilized with ordinary portland cement. Detailed monitoring was then undertaken periodically to determine their performance. The road pavement was constructed on an embankment to ensure good drainage. A good quality surface dressing seal has been maintained. After 19 years of traffic, measured at 1.3 million equivalent standard axles, the marl road bases have performed at least as well as the crushed stone. The cement-stabilized marl road base performed exceptionally well. Stabilization would enable the use of more plastic marls.

Road roughness is the result of a chain of distress mechanisms, and it combines the effects of various modes of pavement deterioration. The common measure of roughness is the international roughness index (IRI). The IRI represents the functional performance of road pavements and serves as an indicator of the structural performance. However, the use of the IRI in setting priorities for maintenance and rehabilitation programs has some flaws. The IRI cannot detect the mode and rate of pavement deterioration that contribute to the surface roughness. In addition, the IRI may be a poor measure of truck ride and the dynamic wheel loads generated by the interaction of heavy vehicles and rough road surfaces. Roughness spectrum can be divided into certain wavebands, with each waveband corresponding to a certain mode of pavement deterioration. The power spectral density analysis of road profiles is used to view the distribution of the various wavelengths within the profile and to show the contribution of each waveband to roughness. Waveband analysis can help overcome the shortcomings of the IRI, and it provides information that helps road authorities in planning rehabilitation programs and managing the road network.

Low-volume roads in areas of seasonal freezing are highly susceptible to damage from trafficking during spring thaw. To minimize pavement damage, many agencies and states impose load restrictions during periods in which damage is most likely to occur. However, the magnitude and duration of reduced or prohibited hauling vary widely among agencies, and an optimal balance between maximizing local economy and minimizing road damage is rarely achieved. The U.S. Department of Agriculture Forest Service and the U.S. Army Cold Regions Research and Engineering Laboratory are evaluating a quantitative technique for removing load restrictions by developing correlations between pavement stiffness and soil moisture. Laboratory tests of the moisture sensors showed them to be accurate and repeatable under adverse freeze-thaw cycling. Preliminary analysis of field data showed that permanently installed time domain reflectometry and radio frequency soil moisture sensors strategically located throughout the forest road network will provide an affordable method for quantitatively determining when to remove load restrictions. Load restriction practices are reviewed, economic ramifications on the forest industry are briefly discussed, and laboratory and field test programs conducted to monitor soil moisture and pavement stiffness are outlined. In addition, instrumentation used for the study is described, observations from one of four national forest pavement test sites are presented, and the ongoing research to develop a method to remove load restrictions is discussed.

At the Sixth International Conference on Low-Volume Roads Yves Provencher, Forest Engineering Research Institute of Canada, presented a paper on the F.A.H.R. rock crusher mounted to a front-end loader. At the same time the Coronado National Forest in Arizona was renting a F.A.H.R. rock crusher for an in-place road-crushing project. In 1997 San Dimas Technology and Development Center, in partnership with the Coronado National Forest, sponsored two demonstration projects to further test the crusher at unique locations to gain additional information from actual field trials. These projects were located on the Rio Grande National Forest in Colorado and the Plumas National Forest in California. The three projects are described here, with results and conclusions gained from the demonstration projects. The concentration is on the characteristics of the processed material. Samples taken from windrows during the crushing operation were tested to determine hardness and gradations before and after crushing. Cost varied from $8 to $26 per m³ including roadbed preparation, crushing, and blading. Rocks and boulders to 405-mm maximum size were crushed. The processed material has a maximum size of 50 to 75 mm. The product produced by the crusher offers a viable alternative for aggregate on a road surface, particularly as a road surface cushion material, where the quality and expense of standard crushed aggregate, such as base course material, are not needed on low-volume roads.

Sasol Chemical Industries produces large quantities of coarse clinker and fly ash as a by-product of the coal gasification process at their Sasolburg plant in South Africa. If this ash could be used as an aggregate in roads, the demand on natural reserves for aggregates would be reduced and an effective method of disposing of these materials would result. The ash is processed at a blending plant in Sasolburg and is marketed under the name Premamix. Trial sections were constructed using labor-based techniques with unstabilized and bitumen emulsion-treated Premamix as a base course material. As the Premamix is a lightweight material and is delivered at a specified moisture content (the optimum moisture content for compaction), it is ideal for labor-based construction of low-volume roads as only spreading and compaction of the layers are required. The trial sections were subjected to accelerated pavement testing with the heavy-vehicle simulator. Although high deflections were measured in the pavement structure, the Premamix performed well under trafficking, even after the base was soaked with water.

The use of the falling weight deflectometer (FWD) as a tool for investigating the structural strength of flexible and rigid pavements is now common. The backcalculation of layer moduli is the primary technique for data interpretation. This technique is cumbersome and expensive to apply to low-volume roads. A simple way of relating the FWD surface deflections to the performance of pavement structures, expressed by the structural number (SN), is presented. The technique is proposed as an alternative to existing methods in Louisiana using Dynaflect data. The relationship was deduced by statistical analysis, using the data collected at the Louisiana Transportation Research Center Pavement Research Facility. The study found that the correlation between the SN and the FWD deflections is satisfactory. Two different relationships are recommended for flexible and semirigid pavements. Both relationships can be applied in a pavement management environment because they allow evaluation of the required thickness for the asphalt overlay. It was found that the structural layer coefficients must be assigned functions of the laboratory moduli determined by the indirect tensile test, not functions of the backcalculated moduli.

For reasons of climate and economy, Australia’s roads are typically of light construction. However, new challenges are emerging as the primary road network nears completion and the volume, mass, and tire pressures of road freight vehicles increase. In 1986, Austroads issued their “Guide to Stabilisation in Roadworks” and, since that time, a great deal of research has been conducted in Australia to improve the in situ stabilization processes from the point of view not only of pavement thickness design but also of construction and rehabilitation practice. In situ pavement recycling by incorporating a cementitious binding agent has long been recognized as an economical way to strengthen pavements. The main problems have been the use of thin layers combined with short working times, resulting in high roughness and subsequent delamination of layers, pumping of fines, and excessive cracking. However, the recent development of deep-lift recycling equipment and specialized binder spreaders, together with the more ready availability of a range of slow-setting binders (granulated slag, fly ash, and lime) and high-performance compaction equipment, have allowed the development of deep-lift stabilization techniques. A brief background of Australia’s roads and recent developments in the use of in situ stabilization in Australia are presented, and recent tests with the accelerated loading facility to assess the suitability of bitumen/cement and slag/lime blends, the latter incorporated in both thin (200 mm) lifts and thick (400 mm) lifts, and the impact of this research on practice, are summarized.

In June 1994, a secondary road pavement section 150 m long was instrumented in Bedford County, Virginia. This pavement section was composed of nine individual sections each 15 m long. Sections 1 through 3 had a limestone base course 100 mm thick (VDOT 21-B); Sections 4 through 6 had a base course 150 mm thick; and Sections 7 through 9 had a base course 200 mm thick. Three sections were stabilized with geotextiles, three were stabilized with geogrids at the base course–subgrade interface, and the other three were kept as control sections. One section from each stabilization category was included in each base course thickness group. The outside wheel path of the inner lane was instrumented with strain gauges, pressure cells, piezoelectric sensors, thermocouples, and moisture sensors. A Keithley 500-A data acquisition system was used to collect instrument responses on-site. Some of the data collected by the instruments are discussed. Section performances based on the instrumentation response to controlled and normal vehicular loading indicated that geosynthetic stabilization provided significant improvement, which was found to be in agreement with rut-depth measurements.

An experimental investigation was conducted on a three-phase cement-asphalt emulsion composite (CAEC), in which asphalt was introduced as a cushion layer in between coarse aggregates and cement mortar matrix by dispersing asphalt emulsion-coated coarse aggregates into cement mortar matrix. Laboratory tests on fatigue, strength, rigidity, temperature susceptibility, and stress-strain relationship were studied to evaluate the mechanical properties of the CAEC. The test results showed that CAEC possesses most of the characteristics of both cement and asphalt—namely, the longer fatigue life and lower temperature susceptibility of cement concrete and the stronger toughness and higher flexibility of asphalt concrete. It is expected that CAEC can be an alternative for semirigid base-course material. However, it slightly reduced the strength compared with control cement concrete.

Pavement subgrades constructed with clay soils can cause significant pavement distress because of moisture-induced volume changes and low subgrade support values. Lime is well known for its ability to stabilize plastic clays; however, portland cement also provides highly effective clay stabilization, usually with the added benefit of higher strength gain. Stabilizing clays with cement or lime can improve subgrade properties at a lower cost than either removing and replacing material or increasing the base thickness to reduce subgrade stress. The clay soil stabilization mechanism for the calcium-based stabilizers portland cement and lime is reviewed. These materials modify soil properties through cation exchange, flocculation and agglomeration, and pozzolanic reaction. Additionally, cement provides hydration products, which increase the strength and support values of the subgrade materials as well as enhance the permanence of the treatment. Comparative laboratory and field performance studies by others, focusing on stabilization of clay soils with portland cement or lime, are critically reviewed. Several factors affecting stabilization are discussed, including stabilizer test procedures, dosage effects to soil properties, mixing, compaction, and gradation and pulverization. Additionally, durability of cement and lime as stabilizers is reviewed, including wetting and drying, freezing and thawing, leaching, and long-term field performance. The research reviewed indicates that, if proportioned and applied properly, both cement and lime can effectively improve the engineering properties of clay soils over the life of a pavement. The results presented provide a guide to the engineer about the property changes to expect when using portland cement and lime with regard to volume stability, strength, and durability.

In surface mining operations, ultra-heavy-haul trucks apply axle loads in excess of 200 t, but the daily load repetitions are low. Road networks for these vehicles have historically been designed empirically, relying heavily on local experience. Increasing vehicle sizes have resulted in unwarranted deformations and excessive maintenance requirements. There was thus a need to consider the transportation problem holistically, taking into account construction and maintenance costs as well as vehicle operating costs. Most opencast mines in South Africa are private endeavors, and all savings will benefit the company. A research project was undertaken in South Africa to develop a management system that takes into account different design factors. The various components of the management system are presented, and the value of its application is demonstrated through case studies. The structural design system, the pavement deterioration system, and the maintenance effectiveness are discussed. The components are then combined to provide total transportation costs and the appropriate maintenance regime to minimize total transportation cost. The system has been applied on several mines, and distinct benefits have been derived. The improved structural design of a new road resulted in a 29 percent savings in construction costs, compared with the tendered price of the empirically designed structure. In addition, improved wet weather trafficabililty was noted. Mines have also used the system as a motivation for improved maintenance equipment and strategies because significant benefits were apparent from the adoption of the maintenance management system.

Road cutslopes and fillslopes account for approximately 50 percent of the total road disturbance area on steep terrain and contribute as much as 60 percent of sediment from forest roads. The significance of erosion control techniques on these vulnerable components of the road prism has become evident in recent years. A study to gain a better understanding of erosion control techniques on road cutslopes and fillslopes is detailed. Sediment and runoff yield from three erosion control treatments and a control were investigated on west-facing 2:1 and 1.5:1 cutslopes and fillslopes, respectively, on a newly constructed road during a 30-month study. The treatments evaluated were a wood excelsior erosion mat, native species grass, and exotic species grass. Factors detected to significantly affect sediment yield from road sideslopes were treatment, time, and treatment-time interaction based on analysis of variance. Significant reductions in sediment yield and runoff were found on all treatments on both the cutslope and fillslope. The erosion mat most effectively controlled erosion losses on both slopes for all study periods.

The electronic cone penetrometer is an important investigation tool of choice for in situ site characterization. Application of this proven concept of the cone penetration test (CPT) to transportation applications is described. A miniature cone penetrometer with a projected cone area of 2 cm² has been developed and implemented in a continuous intrusion miniature CPT system (CIMCPT). This device may be used for rapid, accurate, and economical characterization of sites as well as to determine engineering soil parameters needed in the design of pavements, embankments, and earth structures. The miniature CPT (MCPT) gives finer details than the standard 10-cm² cross-sectional area reference cone penetrometer, which makes it attractive for subgrade characterization, quality control assessment, compaction control of embankments, and assessment of ground improvement effectiveness for transportation infrastructure. In situ calibration of the CIMCPT system was conducted at a highway embankment site in Baton Rouge, Louisiana. MCPT penetration profiles were compared with those obtained with the standard cone penetrometer at the same site. The tip resistance of the MCPT was 10 percent higher than that of the reference CPT. The sleeve friction and friction ratio of the reference CPT were higher than that of the MCPT by 12 and 23 percent, respectively. Calibration was also performed to determine empirical cone factors required for estimating undrained shear strength from MCPT data.

In late November to early December 1995 and February 1996, northern Idaho was hit by heavy rains on a deep snowpack, resulting in two flood and landslide events of historic magnitude. Each of these storms was larger than the previous significant storm, which occurred in January 1974. A study was initiated by the U.S. Department of Agriculture Forest Service to survey and study the effects of the resultant landslides on the Clearwater National Forest, including the effects on the aquatic ecosystem. The results of this study were compared with the estimated average natural sediment resulting from landslides to evaluate the incremental impacts of these recent episodic landslides. They were also compared with the results of a study conducted on the landslides resulting from the January 1974 storm to determine if the landscape was responding more severely to large storms as a result of Forest Service management activities over the past 21 years. The general results of this study indicate that, of the Forest Service management activities, roads are the major contributor; however, they contribute less sediment than natural landslides. The total resultant sediment appears to be within the transport capacity of the aquatic system, and the landslide response in 1974 was similar to the 1995–1996 response. The results of the aquatic ecosystem study were generally mixed, with some habitat parameters indicating degradation, some unchanged, and some improved as a result of the flooding or flooding with landslide sediment.

Pavement design based on the resilient modulus of subgrade soil has been adopted by many transportation agencies following the recommendations of the AASHTO guide for design of pavement structures. Laboratory and field nondestructive tests are generally used to evaluate the resilient modulus of subgrade soil. These methods have shortcomings and limitations and are considered laborious, time-consuming, and expensive. The difficulties associated with the existing methods signify the need for a popular in situ technology for evaluating the resilient modulus of subgrade soil. Among other methods, the cone penetration test (CPT) is fast, simple, and economical and provides repeatable and reliable results. The results of a pilot investigation to assess the possibility of predicting the resilient modulus of subgrade soil from the CPT soundings are presented here. Field and laboratory testing programs were carried out on two types of cohesive soils at the Louisiana Transportation Research Center/Pavement Research Facility. Field tests consisted of CPT soundings using the 15-cm² friction cone penetrometer and the 2-cm² miniature friction cone penetrometer. Laboratory tests included the resilient modulus and physical properties of the investigated soils. The results of the miniature CPT were evaluated and compared with the soundings of the 15-cm² cone at the same site. Both laboratory and field tests were analyzed. Based on statistical analyses, a model was proposed to estimate the resilient modulus from the CPT data and basic soil properties. Predicted values of the resilient modulus are consistent with laboratory measurements.

Low-volume roads are recognized as one of the primary sources of sediment in many watersheds. The authors have carried out research on the details of the complex soil erosion processes occurring on low-volume roads for more than 10 years. An overview of their research summarizes the results of numerous past and ongoing field and computer modeling studies on road erosion processes and the effects of road design on road erosion. The authors have found that insloping and outsloping effects on roads are often overshadowed by the effects of rutting. Most soil erosion on roads is from concentrated flow in ruts or ditches. Adding gravel increases hydraulic conductivity and reduces erosion. Road erosion rates can also be decreased by reducing tire pressure or by removing roads. The authors are developing applications of the Water Erosion Prediction Project model as user-friendly erosion prediction tools for road managers. Further work is required to quantify the effects of current management techniques on water quality and to develop new low-impact road design and management technology.

In recent years, applications of marginal materials, also called nontraditional (either natural or waste products), have been considered in road construction with great interest in many industrialized and developing countries. The use of nontraditional materials in road making is based on technical, economic, and ecological criteria. The lack of traditional road materials and the protection of the environment make it imperative to investigate marginal materials carefully. India has a large network of steel plants located in different parts of the country and many more are planned for the near future. Several million metric tons of iron and steel are produced in these plants. However, along with production of iron and steel, huge quantities of solid wastes like blast furnace slag and steel slag as well as other wastes such as flue dust, blast furnace sludge, and refractories are also being produced in these plants. The iron ores in India, although rich in iron content, are high in alumina content also and as such the volume of slag generated is very high. Normally production of 1 metric ton (1 Mg) of steel generates 1 Mg of solid waste. Although the steel industry slags have their own unique properties and are exploitable for road works, they have never been put to use on Indian roads because of a lack of scientific studies conducted on these materials, nonavailability of proper design and construction standards on them, and the absence of data about the long-term behavior of these materials. In the absence other outlets, these solid wastes have occupied several acres of land around plants throughout the country. Keeping in mind the need for bulk use of these solid wastes in India, it was thought expedient to test these materials and to develop specifications to enhance the use of slags in road making, in which higher economic returns may be possible. Exhaustive and detailed laboratory investigations have been carried out at the Central Road Research Institute, New Delhi, India, to develop suitable specifications for construction of low-volume roads. Based on laboratory investigation results, specifications were developed for construction of low-volume roads in different parts of the country. While specifications were being formulated, attempts were made to maximize use of solid wastes in different layers of the road pavement. Postconstruction pavement performance studies have clearly indicated that these waste materials can be used for construction of low-volume roads with twofold benefits: (a) it will help clear valuable land of huge dumps of slags, and (b) it will also help preserve the natural reserves of aggregates, thus protecting the environment.

Low-volume roads can be a major source of sediment to streams in forest watersheds. For soil erosion from roads to be economically mitigated, the processes that cause erosion need to be understood. The Water Erosion Prediction Project (WEPP), a physically based erosion and sedimentation model, was used for predicting erosion from forest roads that can be described as hillslopes. Watershed applications of WEPP predicted erosion and sedimentation values for insloping roads that can be described as microwatersheds. How well WEPP models insloping roads through a sensitivity analysis and validation process using two studies in the Oregon Coast Range is discussed.

A multiyear research project was conducted to investigate the potential of using municipal solid waste combustion bottom ash as a paving material. Characterization of the ash physical properties, development of the asphalt mix designs, and the bottom ash demonstration project in Laconia, New Hampshire, are discussed here. Laboratory results suggest that the physical properties of the ash are consistent with its use as a substitute for conventional aggregate in asphalt mixtures, the properties of ash are typical of a lightweight aggregate, and the 50 percent ash-asphalt mixture design meets New Hampshire Department of Transportation specifications. An ash demonstration project at 50 percent substitution was successfully placed in Laconia in May 1993. A 5-year period of field performance evaluation indicates that the ash section performs as well as the control section.

Recycling of pavement materials has become a viable alternative to be considered in road maintenance and rehabilitation. Conservation of resources, preservation of the environment, and retention of existing highway geometrics are some of the benefits obtained by reusing pavement materials. In the United States of America, more than 50 million tons (45.36 million Mg) of asphalt paving material are milled annually; recycling into new asphalt paving mixtures is the predominant application. However, large quantities of reclaimed asphalt pavement (RAP) aggregate remain unutilized and further uses should be explored. In the Sultanate of Oman, recycling of pavement materials is not practiced; this study presents a first attempt at evaluating RAP aggregate. The reuse of RAP aggregate could be economically attractive in Oman because certain regions of the country experience virgin aggregate shortage. Furthermore, rehabilitation of the road network would provide a valuable resource to be considered in highway construction. A laboratory evaluation of RAP and RAP-virgin aggregate mixtures as road base and subbase materials is described here. Physical, compaction, and California bearing ratio tests were conducted on the following RAP/virgin aggregate blends: 100/0, 80/20, 60/40, 40/60, 20/80, and 0/100 percent. Initial results indicate that RAP could be expected to replace virgin aggregate in the pavement subbase structure with satisfactory results if the RAP material were mixed with virgin aggregate. Best results were obtained for the 60/40, 40/60, 20/80, and 0/100 percent RAP/virgin aggregate blends. Higher dry density and CBR values are obtained as virgin aggregate content is increased. Based on a comparison with standard paving materials used in the Sultanate of Oman roads, the stabilized RAP material appears to be able to function as well as a conventional subbase material. However, only minimal use of RAP (about 10 percent) can be expected in road bases.

The performance of lime and fly ash-stabilized base as an alternative to soil-cement-stabilized base for flexible pavement systems on reconstructed highways in Louisiana is evaluated in this study. Historically Louisiana has used soil cement for most flexible base construction because of its low cost, high compressive strength, and ease of construction. However, soil cement is subject to excessive cracking due to shrinkage, which may decrease the expected pavement life. Lime and fly ash bases exhibit many of the same properties as soil-cement bases with potential for less shrinkage cracking. Lime and fly ash (Class C fly ash) test sections were installed on two Louisiana highway reconstruction projects in the northwestern part of the state. For each project, two 0.4-km (0.25-mi) test sections with different percentages of lime and fly ash were constructed. The remainder of each project was constructed with 8 percent soil-cement base by volume. On both projects, the first test section used 2 percent lime and 4 percent fly ash by weight for stabilization and the second test section used 3 percent lime and 6 percent fly ash. Test specimens were molded in the field during construction by using stabilized base material taken from the roadway immediately before compaction. Laboratory test specimens were made later with materials taken from, but not mixed at, the construction sites. Both field and laboratory samples were tested in unconfined compression at 7, 28, and 56 days. The overall unconfined compressive strength of lime and fly ash was 30 percent lower than that of soil cement.