bluuebunny/crossref_metadata_2025 huggingface dataset:
Relating In Situ Properties of Cement-Bound Bases to Their Performance
Authors: Thom N. H. , Cheung L. W.
Published: April 2007

A rationale for explanation of the in situ layer modulus expected from a cementitious base is presented. It is assumed that all such bases crack to various degrees, depending on material strength and other pavement parameters, under the influence of shrinkage, temperature changes, and trafficking. The layer modulus is shown to be a function of hinge and slip effects at cracks, as well as the intrinsic material modulus, and simple, practical, but fundamental-based equations are given for its prediction. The point that any given layer modulus could, in principle, be due to any of several different combinations of material modulus, crack spacing, and condition is made, and so careful interpretation is vital. The use of the predictive equations is then demonstrated in six selected cases, covering materials ranging from cracked pavement-quality concrete to lime- and cement-stabilized clay, and the equations are seen to enable the measured layer moduli to be interpreted sensibly. Finally, two examples are given. In these examples similar layer moduli relate to two quite different materials and conditions, which have given rise to different pavement performances. The weaker material resulted in a better combination of crack spacing and condition and a longer-lasting pavement, whereas the stronger material resulted in a pavement very susceptible to reflective cracking. The conclusion is drawn that, for optimum pavement performance, the key is to limit the amount of slip at cracks by ensuring good interlock as well as adequate intrinsic material strength and stiffness. A slowly curing material is ideal.
Laboratory Study of Feasibility of Stabilizing Zinc Clinker and Road Millings To Produce Low-Permeability Pavement Material
Authors: Lawton Evert C. , Heimdal Tor M. , Roadifer John W. , Robinson Kimberley S.
Published: April 2007

An international mining company has funded research to develop a lowpermeability pavement material by stabilizing on-site waste materials (zinc clinker and road millings) at a zinc processing plant in the mid-western United States. The need for development of this material has arisen from concerns of the state environmental protection agency (EPA) that rain is leaching zinc from stockpiles of clinker, thereby contaminating the surface soils, drainage ditches, and groundwater on the site. The desired engineering properties of the stabilized material are as follows: ( a) the material must have sufficiently low permeability to act as an “impermeable” liner, ( b) the material must bind the zinc to the clinker so that it does not leach out, and ( c) the material must be stiff and strong enough to serve as a pavement base course and wearing surface. Laboratory tests were conducted with various stabilized combinations of asphaltic road millings, zinc clinker, and local clay from a zinc processing plant in the midwestern United States to determine whether a lowpermeability pavement material could be produced. Two methods of stabilization were studied: ( a) one with portland cement and ( b) one with a combination of three cold-mix additives (a binder, a stabilizer, and a sealant). The primary types of laboratory tests conducted were unconfined compression tests with cement-stabilized materials, Marshall stability tests with cold-mix-stabilized materials, and leachate-permeability tests with both types of stabilized materials. A design mixture was produced by the addition to the waste materials of the three proprietary coldmix additives (a binder, a stabilizer, and a sealant) and a local clay that meets all three requirements in tests with laboratory-prepared specimens. Field tests are needed to verify that these attributes can be produced by full-scale construction techniques. In addition, laboratory and field tests are needed to determine the durabilities of these stability materials for the repetitive traffic loads and environmental conditions to which pavement systems are subjected.
Soil Stabilization with Sodium Chloride
Authors: Singh Gurdev , Das Braja M.
Published: April 2007

The potential of sodium chloride as a stabilizing agent for highway construction has been investigated. Literature covering laboratory and field studies since the early 1900s is briefly reviewed. The results of laboratory tests with mixtures of several soils and a gravel with a commercial montmorillonite clay stabilized with rock salt and brine are presented. The laboratory study included the Atterberg limits test, compaction test, unconfined compression test, California bearing ratio test, indirect tensile strength test, and cyclic triaxial test. The cyclic triaxial tests were conducted to determine resilient modulus and permanent deformation under cyclic loading as well as Poisson’s ratio. The beneficial effects of sodium chloride stabilization are discussed.
Estimating Potential Aggregate Interlock Load Transfer Based on Measurements of Volumetric Surface Texture of Fracture Plane
Authors: Vandenbossche Julie M.
Published: April 2007

The volumetric surface texture (VST) test was developed at the University of Minnesota to provide an estimate of the load transfer potential available through aggregate interlock across a concrete fracture plane. It can also provide an estimate of the abrasion that has taken place since fracture. A study was undertaken to validate the VST concept and test procedures. The factors investigated in this study include the effects of aggregate characteristics on measured surface texture and the effects of measured surface texture on crack and undoweled joint performance, as indicated by deflection-based load transfer efficiency. Deflection, load, and crack width data were collected for both field and laboratory slabs, and VST testing was performed with companion specimens for these slabs. This study has shown that the VST test provides a means of accurately measuring surface texture so that the selection of concrete aggregates can be performed with consideration of potential aggregate interlock at cracks and undoweled joints. Performance prediction equations were developed to provide an early indication of how cracks and undoweled joints will perform before a particular aggregate size, type, gradation, or blend is used in an actual pavement.
Permanent Deformation of a Granular Base Material
Authors: Uzan Jacob
Published: April 2007

An approach to the characterization of unbound pavement materials for mechanistic analysis of pavements is presented. To predict permanent deformation, it is necessary to evaluate the residual properties of the materials. A method for evaluation of both the resilient and residual properties from repeated load testing is recommended. The residual properties of the material are described by three functions: ( a) the slope of the permanent strain versus number of load repetitions, S, on a loglog scale, ( b) the loading stress-strain curve of the first cycle, and ( c) the resilient properties of the material. The framework for evaluation of the permanent characteristics is presented. It is based on the theory of elastoplasticity. Two models developed by Vermeer and by Desai [hierarchical single-surface (HISS) model] are described. Test results conducted with a high-quality base course are presented and analyzed. It is found that ( a) the slope S depends slightly on the confining pressure and ( b) both models describe the dependence of total strain on stress. The HISS model with eight parameters fits the results better than the Vermeer model.
Site Design and Pedestrian Travel
Authors: Hess Paul M. , Vernez Moudon Anne , Catherine Snyder Mary , Stanilov Kiril
Published: April 2007

Research findings are summarized regarding the relationship between site design and pedestrian travel in mixed-use, medium-density environments, and recommendations are set forth for improving pedestrian facilities in suburban neighborhoods. A quasi-experimental method is used to study pedestrian volumes into 12 neighborhood commercial centers in the central Puget Sound region. Sites were matched for population density, land use mix, and income, but they varied in terms of neighborhood site design as measured by block size, and by the length and completeness of sidewalk systems. Urban sites with small blocks and extensive sidewalk systems were found to have, on average, three times the pedestrian volumes of suburban sites with large blocks and short, incomplete sidewalk systems. There are, however, many suburban pedestrians, with volumes varying between 50 and 103 people per hour walking into the suburban commercial centers studied. The majority of suburban pedestrians use streets with sidewalks where available. Also, suburban pedestrians are more likely both to jaywalk and to use crosswalks than their urban counterparts. People under age 18 and people of color were overrepresented in suburban pedestrian populations compared with their makeup in the local residential population. These findings point to the importance of providing facilities to improve pedestrian safety for people who cannot or do not want to drive in such areas. Recommendations include completing sidewalk networks, creating walkways to connect all building entrances to public sidewalks, and increasing the opportunities for pedestrians to cross streets safely.
Study of Bicycle Lanes Versus Wide Curb Lanes
Authors: Hunter William , Stewart J. , Stutts Jane
Published: April 2007

A comparative analysis of bicycle lanes (BLs) versus wide curb lanes (WCLs) was done. The primary analysis was based on videotapes of almost 4,600 bicyclists from 48 sites in Santa Barbara, California; Gainesville, Florida; and Austin, Texas. The videotapes were coded to evaluate operational characteristics and conflicts with motorists, other bicyclists, or pedestrians. Significant differences in both operational behaviors and conflicts were associated with BLs and WCLs, but they varied depending on the behavior being analyzed. Wrong-way riding and sidewalk riding were much more prevalent at WCL sites compared to BL sites. The aggregated data showed that significantly more motor vehicles passing bicycles on the left encroached into the adjacent traffic lane from WCL situations compared to BL situations. Proportionally more bicyclists obeyed stop signs at BL sites; however, when a stop sign was disobeyed, the proportion of bicyclists with both "somewhat unsafe" and "definitely unsafe" movements was higher at BL sites. The vast majority of observed bicycle-motor vehicle conflicts were minor, and there were no differences in the conflict severity by type of bicycle facility. Bicyclists in WCLs, however, experienced more bike-pedestrian conflicts, whereas bicyclists in BLs experienced more bike-bike conflicts. The overall conclusion is that both BL and WCL facilities can and should be used to improve riding conditions for bicyclists. The identified differences in operations and conflicts appeared to be related to the specific destination patterns of bicyclists riding through the intersection areas studied and not to characteristics of the bicycle facilities.
Development of Cemented Sand Module for Electric Cone Penetrometer
Authors: Bloomquist David , Hand Randell S. , Brian Anderson J.
Published: April 2007

A stratum of cemented sand can cause numerous geotechnical design problems. Extensive research has been conducted to determine both the properties of cemented sand and their effects on the engineering response of soil. A cone penetration test module was developed at the University of Florida to detect the presence and strength of these materials. After design and construction were complete, the prototype module was field tested in sand without cementation and again at a site with possible cementation. Development, calibration, and field testing of the module are discussed, as are preliminary recommendations for its potential use.
Comparison of Piezocone and Laboratory Soil Parameters for Bridge Foundation Design on Clays: Case Study in Massachusetts
Authors: Mitchell Travis J. , DeGroot Don J. , Lutenegger Alan J. , Ernst Helmut , McGrath Valerie
Published: April 2007

Results of a case study to demonstrate the use of the piezocone (CPTU) for selection of soil parameters for design of bridge foundations at a clay site in Massachusetts are presented. The test site is the location of several timber-supported bridges that have suffered significant deck and foundation deterioration and need replacement. The soil profile generally consists of 1 to 10 m of fine sand and silt, followed by 45 m of a low-plasticity marine clay that rests on a very dense fine to coarse sand. The site investigation consisted of traditional drilling and sampling techniques, field vane testing, and CPTU profiling. Shelby tube samples were used for laboratory tests, including basic soil characterization and measurements of stress-strain-strength behavior through oedometer and K0 consolidated direct simple shear tests. Results from laboratory tests showed that some of the tube samples had suffered moderate to high levels of sample disturbance, making them unreliable for laboratory stress-strain-strength testing. A comparison of the laboratory results with the CPTU profiles showed that the CPTU provided excellent information on soil stratigraphy and good comparison with the laboratory-determined stress history and undrained shear strength profiles. The CPTU test program involved less time and expense than the laboratory test program and was not susceptible to sample disturbance effects. This case study suggests that state departments of transportation should consider the CPTU as the instrument of first choice in site characterization programs for design of bridges founded on soft clays.
Use of Biocells for Enhanced Bioremediation of Soils Contaminated with Heavy Petroleum Hydrocarbons
Authors: Zappi Mark , Jing Yue , Albritton Gayle , Crawley Al , Singletary Judy , Tarbutton Ronald , Hall Neil
Published: April 2007

Petroleum products are composed of many organic chemicals and are recognized as the most prevalent contaminants found in contaminated soils and sediments. Of particular regulatory interest are simple aromatics and polycyclic aromatic hydrocarbons, which are toxic and carcinogenic at low levels. Many treatment processes have been used for treatment of fuels. Biotreatment appears to hold the most promise as a cost-effective process that can destroy petroleum hydrocarbons on site. The potential for bioremediation was evaluated on a soil contaminated with heavy motor oil from years of dumping waste oils from an automotive garage. This soil was selected because it posed a unique challenge to bioremediation and therefore provided the framework for evaluation of various process enhancements. A series of shake-flask experiments (500-mL flasks filled with 25 percent w/w water-soil slurries) was performed to determine the extent and rate of removal of total petroleum hydrocarbons (TPH) using various soil amendments, including nutrients, cometabolites, a nonionic surfactant, and microbial seeds. The information from the shake-flask experiments was used to plan a series of experiments that used eight 30-L (8-gal), bench-scale biocell reactors. The results of the biocell experiments show that approximately 80 percent of the TPH could be removed using a treatment system that consisted of nutrient and surfactant amending with bioaugmentation with activated sludge.
Vehicle-Ownership Model Using Family Structure and Accessibility Application to Honolulu, Hawaii
Authors: Ryan James M. , Han Gregory
Published: April 2007

Vehicle ownership plays a key role in determining the number of trips made by a household and the modes that the household will use to make those trips. Predicting vehicle ownership is a challenge due to the complexity of relationships affecting the choice of vehicles for a particular household. The income of the household, the accessibility of activities by alternative modes, and the family makeup of a household all affect the choice of the number of vehicles. The Honolulu metropolitan statistical area, which encompasses the island of Oahu, is the primary study area. On Oahu, vehicle ownership varies widely, from the dense neighborhoods in Waikiki to the semirural areas on the fringe of the region. Consequently, the vehicle-ownership model will be a crucial component of the new travel forecasting models for the island. Using 1995 Oahu household interview survey data, a vehicle-ownership model that takes into account income, accessibility, and household family structure has been estimated and found to predict rather accurately the shares in each vehicle-ownership class by geography, household size, and number of workers. In addition, 1990 census data have been used to test a variation of the vehicle-ownership model on several other American cities such as Atlanta, Kansas City, San Francisco, and New York. The resulting models for these regions parallel the Honolulu vehicle-ownership model very closely in structure and statistical significance, thereby demonstrating the model structures’ transferability between regions.
Stochastic User-Equilibrium Formulations for Extended-Logit Assignment Models
Authors: Prashker J. N. , Bekhor S.
Published: April 2007

New stochastic user-equilibrium formulations are presented. In the transportation literature, the “logit assignment” stands for a stochastic user-equilibrium model in which the multinomial logit is the route-choice model. Efficient algorithms using this mathematical formulation were proposed to solve the logit assignment. However, the use of the logit function for route choice has some theoretical drawbacks. In typical transportation networks, many routes have common links, and the structure of the model is not able to account for these common links because the probability for choosing a route is computed based solely on the total route cost. Recently, extended logit-based models were proposed to overcome the overlapping problem and keep the analytical tractability of the logit function. It is demonstrated how extended logit models—such as the Cross-Nested Logit and the Paired Combinatorial Logit—can be derived from more general entropy-type formulations, thus allowing the use of existing (and yet under development) algorithmic solutions for the more general logit-family stochastic assignment model.
Modeling the Generation and Organization of Household Activity Stops
Authors: Bhat Chandra R. , Carini Jay P. , Misra Rajul
Published: April 2007

A model is proposed for household-stop generation and organization and is applied to examine household-shopping stop-making behavior using a Boston-area household travel survey. The model accommodates the ordinal, discrete nature of stop-making and incorporates a comprehensive, policy-sensitive measure of accessibility. Empirical results provide useful insights into the effect of household characteristics and accessibility to shopping opportunities on shopping-stop behavior. The application of the model is demonstrated by examining the effect of an increase in highway costs and changes in land use patterns on shopping-stop generation and organization.
Caltrain Rapid Rail Plan
Authors: Nash Andrew Butler
Published: April 2007

The results of Caltrain’s Rapid Rail Study are described. The purpose of the study was to develop a long-range strategic capital investment plan for the commuter railroad. The plan addressed rehabilitation, upgrades, and expansion projects. The study consisted of seven major steps: developing a future service strategy, an evaluation of existing conditions, identification of rehabilitation and upgrade projects, analysis of expansion projects, project prioritization, development of a financial plan, and development of recommendations. The study is interesting in that it combines basic rehabilitation and long-term planning to improve the efficiency of the planning and construction process. This, in turn, will help Caltrain maintain and improve service for customers with minimum disruption.
Maximizing Operating Reliability in Design of Long Single-Track Light Rail Transit Lines
Authors: Dure Davis
Published: April 2007

At 79 km, the proposed Southeastern Pennsylvania Transportation Authority Cross County Metro would be the longest light rail transit (LRT) line in North America. The system would use an existing single track constructed on embankment, and adding a second LRT track over the entire distance would be prohibitively expensive. However, operating a single-track line of this length at 15-min headways would pose an unprecedented operational challenge using conventional approaches to siding location. The longer the line, the greater the likelihood that a late train will delay opposing trains and cause further delays. A methodology for locating passing sidings on single-track lines to mitigate the problem of cascading delays, even on long lines, is proposed. Unlike the conventional practice of locating sidings at the midpoint of scheduled meets, the sidings near the outer ends of the line are located off-center relative to the meet point, and are longer than those in the middle of the line. This tailors the length of siding cushion on either side of the meet point to match the risk of delay, and maximizes the effectiveness of the full length of each siding. Simulation results indicate that long single-track lines can be designed successfully to avoid delay propagation. However, the siding location methodology leaves little room for compromise. In addition, the resulting sidings are forever wedded to a specific operating plan. Station stopping patterns and operating speed cannot be changed once the sidings are in place, with headways only in multiples of the design headway.
Trolley Shoe Carbon Inserts: Testing for Success
Authors: Hao Elson
Published: April 2007

The method used by the San Francisco Municipal Railway (Muni) to evaluate the wear of trolley-shoe carbon inserts is presented. The trolley shoe is that part of the bus that is directly in contact with the overhead lines. To extend the life of the trolley shoes and allow for their reuse, the cheaper carbon inserts are used as sacrificial material to take care of the wear that occurs between the overhead line and the trolley shoe. For years, Muni operated its fleet of trolley buses using carbon inserts that were purchased solely based on the price of the inserts. Although it would appear that the cheapest carbon inserts provided the best deal for the company, in reality the company was spending a lot more in terms of ( a) lost revenue due to equipment failure, ( b) damage to equipment, and ( c) unscheduled maintenance cost. Muni’s materials management system database had a list of six different grades of carbon inserts. These grades of carbon inserts were included in the database as per the recommendation of the vendors. However, these grades of carbon inserts were never evaluated for compatibility with the bus or overhead system. Consequently, some would wear after one day of service although others would last 5 days or more. This test was conceived to identify the most suitable grade of carbon insert for Muni’s trolley coaches. For the test, weight loss was used to measure carbon wear instead of the change of height or thickness of the insert. To limit the variables affecting the inserts during the test, different grades of inserts were paired during service. Based on the test results, the number of approved carbon grades for use in Muni’s trolley fleet was reduced from six to two and 972.6 km (600 mi) was established as an acceptable service life for the inserts.
Capacity of Single-Lane Roundabouts with Slow Traffic
Authors: de Leeuw Martijn A. M. , Botma Hein , Bovy Piet H. L.
Published: April 2007

Many roundabouts have been built in the Netherlands over the last 15 years. A much-debated issue has been whether to give slow traffic, especially cyclists, priority. Recently, a general recommendation was made: priority for slow traffic inside built-up areas and the reverse for rural roundabouts. Because the implementation of this recommendation could result in a large number of roundabouts with priority for slow traffic, there was a need to develop a method that determined the capacity and delay, taking the influence of slow traffic fully into account. In this study such a model was developed. It is an analytical model that combines parts of existing analytical submodels, with extensions. Motorized traffic entering a roundabout is confronted with three conflicting streams: the well-known circulating stream of vehicles on the roundabout, the parallel slow traffic blocking the entry, and the circulating stream of slow traffic at the next downstream exit that blocks the outgoing motorized vehicles and as a consequence can also block the entry. The model was calibrated successfully with observations from two one-lane saturated roundabouts. With the model not only the capacity per entry can be calculated but also the capacity of the total roundabout, given a relative origin-destination matrix of fast and slow traffic.
Passing Activity on Two-Lane Highways in Spain
Authors: Romana Manuel G.
Published: April 2007

Presented in this paper are the results of research on passing activity on two-lane highways in Spain. The data were gathered on three highways in the province of Madrid, Spain (M-111, M-600, and M-607). Measurements were carried out in 3-h periods, on plain or slightly sloping ground, and for daily or weekly peak periods. The average daily traffic and rate of heavy vehicles in 1991 were, sorted chronologically, 9,500 (6.4 percent) on the M-607, 9,800 (5.1 percent) on the M-600, and 8,100 (8.6 percent) on the M-111. Passing maneuvers were accounted for by examining the differences in order of vehicles at entry and exit points for each road section. A total of 780 passing maneuvers were detected. Passing rates were studied, in particular the variation of passes made with flow rates, both in the direction of passing and in the opposing direction. Maximum passing rates are suggested for each opposing flow rate, and it is indicated that passing is most effective for balanced flows of between 500 and 700 veh/h.
Simulation of Large Freeway and Arterial Network with CORSIM, INTEGRATION, and WATSim
Authors: Prevedouros Panos D. , Wang Yuhao
Published: April 2007

Simulation of a large integrated (street and freeway) network with three state-of-the-art software programs is presented. The 20-centerline-km network includes three on-ramps, three off-ramps, an on-and off-ramp weaving section, and a high design arterial with 11 signalized intersections. After considerable modifications to default settings, all three software programs were able to replicate field-measured volumes well. INTEGRATION required extensive modifications to approximate complex signal timing plans and had problems with lane alignment on the wide arterial. CORSIM’s FRESIM component had difficulty with vehicles that miss their destination and required car-following parameter settings corresponding to unusually high capacities to produce good results. WATSim needed the fewest modifications, and it was primarily sensitive to merging and acceleration lengths. WATSim and CORSIM speeds were close to each other. INTEGRATION’s simplified treatment of signalization produced higher street link speeds.
Method To Preprocess Observed Traffic Data for Consistency: Application of Fuzzy Optimization Concept
Authors: Kikuchi Shinya , Miljkovic Dragana
Published: April 2007

For any of the algorithms of an intelligent transportation system (ITS) to be effective, high-quality data are essential. In reality the data obtained in the field carry significant noise because of imperfections in the measurement devices. For example, the traffic volume data on different links of a network must be consistent and must satisfy the conservation of flow, but this condition is rarely met by the observed values. A way to adjust the observed values so that the adjusted values satisfy predetermined conditions, such as the flow conservation equations or any consistency requirements in a network, is proposed. The adjusted values are found to be as close to the observed value as possible by using the concept of fuzzy optimization. The method can be applied to any network configuration and can also estimate the traffic volumes for links for which traffic volume data may be missing. The method is so general that it can be applied to various transportation problems in which a set of observed or calculated values must be adjusted to satisfy some predetermined rigid relationships among the parameters.
Artificial Intelligence Search Algorithms for Dynamic Traffic Routing
Authors: Sadek Adel W. , Smith Brian L. , Demetsky Michael J.
Published: April 2007

The development of sound routing strategies for dynamic traffic routing is a complex task that requires the use of an automated traffic-routing decision support system (DSS). In this study, heruistic search algorithms were used to build prototype DSSs for on-line traffic routing. Specifically, two DSSs were developed for a real-world highway network: the first was developed by using simulated annealing (SA) and the second was constructed by using genetic algorithms (GAs). The use of such algorithms allows more accurate modeling of traffic dynamics than is possible by traditional analytical techniques. To evaluate and compare the performances of the developed DSSs, a test set consisting of 10 randomly generated problems was used. Results demonstrated that the DSSs are capable of yielding high-quality solutions in a reasonable amount of time. In addition, for on-line traffic routing, SA tends to perform better than GAs.
Microsurfacing Usage Guidelines
Authors: Smith Roger E. , Beatty C. Keith
Published: April 2007

Microsurfacing is used as a surface seal to establish skid resistance on pavements, to fill ruts in asphalt concrete pavements and chain-wear depressions on portland cement concrete pavements, to reduce weathering and raveling on asphalt concrete pavements, and to surface bridge decks. Usage guidelines for applying microsurfacing on asphalt concrete pavements were developed while working on a project for the Texas Department of Transportation (TxDOT). These guidelines are based on information collected from published literature, personnel experienced in using microsurfacing, TxDOT personnel, industry personnel, and the project staff’s experience developed during the project. Special attention was directed at identifying those pavement types, conditions, and problems that normally could be addressed with microsurfacing. Provided is the following information: a short description of microsurfacing, its use as a surface treatment, its use as a rut filler, the types of pavement problems for which the treatment would be appropriate, the requirements of the pavement for treatment with microsurfacing, recommended analysis procedures to decide if microsurfacing is appropriate for a selected section of pavement, layer thicknesses, and the time of opening to traffic.
Life-Cycle Cost Analysis for Zinc and Other Protective Coatings for Steel Structures
Authors: Weyers Richard , Goodwin Frank E.
Published: April 2007

Life-cycle cost models for corrosion-protection coating systems for structural steel are presented. The models are a first-construction/replacement model and a rehabilitation model considering a finite service life and perpetual service. The model development considered comparison period, price and service lives, interest rate, inflation and taxes, and sensitivity and risk analysis. Mathematical expressions are presented for the models. A Virginia bridge superstructure example is presented for painting versus a galvanized coating system considering a 75-year design life. The example illustrates the cost-effectiveness of selecting the galvanized coating system over paint for an environmental exposure condition in Virginia.
Evaluation of Stripping in Virginia’s Pavements
Authors: Maupin G. W.
Published: April 2007

Virginia has struggled with stripping of asphalt mixes since the 1970s. Initially, chemical antistripping additives were used; eventually, hydrated lime was required, under certain conditions, when it proved to be effective in a limited set of field tests. The specifications were then changed to require hydrated lime or a chemical additive that could produce a tensile strength ratio (TSR) equivalent to that obtained with hydrated lime. Because of this change, it was believed that chemical additive manufacturers made improvements to produce a new generation of additives that were superior to those previously available. In 1991, a small field study was initiated in Virginia to determine the performance of the new-generation additives and hydrated lime. The pavements still showed significant stripping. A follow-up survey including 74 sites scattered throughout the state verified this finding. No significant difference in the amount of stripping was detected between the mix types or between mixes that used chemical additives and those that used hydrated lime. In the initial study, the TSR test did not indicate accurately the stripping performance of the mixes. Because of this work, the Virginia Department of Transportation is considering changing its density specification and additional research is being conducted.
Laboratory Evaluation of Clogging Potential of Porous Asphalt Mixtures
Authors: Fwa T. F. , Tan S. A. , Guwe Y. K.
Published: April 2007

A laboratory test to assess the clogging potential of porous asphalt mixtures is useful as part of a rational design procedure of using these mixtures for construction of pavement surface friction courses. Two prerequisites for the laboratory assessment are ( a) the ability to measure an engineering parameter indicative of the mixture’s drainage capacity, and ( b) the availability of a repeatable procedure of introducing materials into the mixture to create clogging. A laboratory clogging test to cause deterioration in the drainage capacity of typical porous mixtures is described here. Monitoring of the changes in drainage capacity during the test is made possible by the use of recently developed equipment to measure permeability. The proposed clogging test procedure was applied to evaluate four porous asphalt mixtures. Test results suggest that the procedure was able to ( a) produce significant degrees of deterioration in the drainage capacities of the mixtures, and ( b) differentiate the different behaviors of the four mixes under the clogging treatment of the test.
Effect of Gradation on Asphalt Mixture Performance
Authors: Haddock John , Pan Changlin , Feng Aiwen , White Thomas D.
Published: April 2007

Phase I of National Pooled Fund Study No. 176, “Validation of Strategic Highway Research Program (SHRP) Asphalt Mixture Specifications Using Accelerated Testing,” has been completed. One of the topics addressed in this project was the effect of gradation on asphalt mixture performance. The purpose of Phase I was to evaluate sensitivity of tests to changes of gradations within the framework of Superpave aggregate specifications. Tests included in the study were prototype scale accelerated pavement tests, laboratory scale wheel-tracking tests, and triaxial tests. Mixtures reported on here included one asphalt (PG 64-22), one coarse aggregate (limestone), and one limestone sand (fine aggregate angularity value of 44). Mixtures in the study have gradations above, through, and below the restricted zone. Results indicate that tests used are sensitive to changes in gradation and aggregate types.
Use of the Hamburg Wheel-Tracking Device for Evaluating Moisture Susceptibility of Hot-Mix Asphalt
Authors: Izzo Richard P. , Tahmoressi Maghsoud
Published: April 2007

Laboratory testing of hot-mix asphalt (HMA) to evaluate moisture susceptibility has improved over the past several decades. Within the past 8 years, the Hamburg wheel-tracking device (HWTD) has gained prominence in evaluating HMA for moisture susceptibility. There are no standard test methods or specifications established for this testing device. Laboratory repeatability of the test, testing configuration, test temperature, and capability to evaluate effects of antistripping additives in HMA were evaluated in this study. The HWTD was observed to be very repeatable where six replicate tests provided consistent test results. The device yielded repeatable results for mixtures produced with different aggregates and with test specimens fabricated by different compacting devices. The conventional testing configuration was altered so that cylindrical test specimens fabricated with a Superpave gyratory compactor could be used in lieu of rectangular slabs. Results indicate that cylindrical specimens compacted with the SGC could be used for moisture evaluation in the HWTD for comparative evaluation of materials. Typically, testing with the HWTD is performed at 50°C. Six mixtures were fabricated with and without antistripping additives and tested at 40°C and 50°C. Mixtures were modified with hydrated lime and a liquid antistripping additive and all were mixed with AC-20. Test results have indicated that mixtures with hydrated lime perform best, followed by those modified with liquid antistripping additive, and worst were those without any additive at 40°C. Inconsistent trends were observed at 50°C. The HWTD properly predicted performance of the mixtures modified with antistripping additives at 40°C.
Selection of Laboratory Test Specimen Dimension for Permanent Deformation of Asphalt Concrete Pavements
Authors: Weissman Shmuel L. , Harvey John , Sackman Jerome L. , Long Fenella
Published: April 2007

Permanent deformation of asphalt concrete pavements is a critical distress mechanism. Efforts are currently being made to understand, analyze, and predict permanent deformation response. To characterize asphalt concrete, laboratory testing is routinely performed. The concept of the representative volume element for determining the minimum specimen dimensions to obtain reliable and repeatable laboratory test data is discussed here. Two conceptual laboratory tests that are currently used to characterize asphalt concrete—the restricted triaxial test and the simple shear test at constant height—are also discussed. The imperfections of both tests are investigated and recommendations for specimen size and the aspect ratio for each of the tests are made.
Kenya Bituminous Materials Study
Authors: Wambura John H. G. , Maina John , Smith Harry R.
Published: April 2007

The causes of premature failures in asphalt surfacings in Kenya have been identified. Two heavily trafficked sites had suffered top-down cracking, associated with severe hardening of the asphalt in the surface of the wearing course, whereas others had deformed plastically. Tests confirmed that reduction of voids in the mix (VIM) to less than 3 percent resulted in a high risk of plastic deformation under heavy traffic. Difficulties arise in designing asphalt mixes for heavily trafficked roads in countries where laboratory equipment is limited. These difficulties include selection of appropriate levels of compaction in the Marshall test and predicting the combined effect of asphalt hardening and secondary compaction. Use of a refusal density test is recommended to determine a reference density to ensure that 3 percent VIM will be retained. The importance of preconstruction field trials to establish the workability of such a mix is emphasized. Acceptable results were most easily obtained with aggregate gradings for binder course or roadbase layers that fell below the Superpave restricted zone. Such materials must be sealed to prevent premature top-down cracking associated with age hardening of asphalt in the layer surface. Performance tests, such as those used in this study, are ultimately required to ensure good performance of asphalt surfacings. Until developing countries can acquire the equipment required for these tests, it is recommended that the procedure described here be used to reduce the large number of premature failures such as those currently occurring in Kenya.
Difficult Nature of Minimum Voids in the Mineral Aggregate: Historical Perspective
Authors: Coree Brian J. , Hislop Walter P.
Published: April 2007

Several researchers have recently discussed problems in achieving the minimum voids in the mineral aggregate (VMA) requirements specified in Superpave volumetric mix design. The minimum VMA requirements are often difficult to achieve; they can “fail” mixes that have acceptable performance records and they may require a higher asphalt content, leading to higher project costs. To address these issues, the background and logic behind the minimum VMA requirement are reexamined. A review of asphalt mix design methods indicates that a minimum VMA requirement was not used until the 1950s, when Norman W. McLeod almost single-handedly advanced VMA to a critical design parameter. In 1962, the Asphalt Institute specified VMA as a Marshall mix design requirement, but as late as 1985 it was still misused by many highway agencies. Only through the Strategic Highway Research Program and the implementation of Superpave has the minimum VMA requirement become a design standard. The literature review uncovered several problems with specifying minimum VMA: ( a) the field data from which the minimum VMA requirements were established could not be found in the literature, ( b) the original VMA requirements were based on Marshall compaction, and ( c) the precision of the testing necessary for measuring VMA is not good enough for rigid enforcement of VMA specifications. In light of the information presented, it appears clear that the minimum VMA requirements need to be reexamined in light of Superpave and validated with field data.
Capacitated Demand Changes as a Project Evaluation Measure
Authors: Gur Yehuda J.
Published: April 2007

Given a transport network and fixed demand (expressed as an origin-destination trip matrix), “capacitated demand” is defined as the portion of the given demand that can be served by the network without violating capacity constraints on any of the network’s facilities. A significant performance measure of a proposed project in a congested area is the amount of change in the capacitated demand, which is caused by the project: the bigger the change, the bigger the contribution of the project to the productivity of the network and its ability to serve the transport needs. Recently, a modified procedure for the evaluation of transport projects (the Pratt procedure) has been implemented in Israel. It uses capacitated demand as a major evaluation measure. The capacitated demand measure and methods for its estimation are described, as are some of the unique features of Pratt and how the new measure is incorporated into it.
Video Enforcement of High-Occupancy Vehicle Lanes: Field Test Results for I-30 in Dallas
Authors: Turner Shawn
Published: April 2007

A study was conducted to assess and test promising technologies for high-occupancy vehicle (HOV) lane enforcement. After a qualitative assessment of video, automatic vehicle identification, and infrared machine vision technologies, the study was suspended because no preferred infrared machine vision technology was available for testing. The study was resumed when a vendor demonstrated promising video technology. The HOV enforcement and review (HOVER) system was then developed for an operational test on the I-30 contraflow HOV lane in Dallas, Texas. The results of an independent evaluation by Texas Transportation Institute indicated that the HOVER system, in its current state, could support a program that mails HOV information to suspected violators. The study’s limited budget prevented several improvements that could expand the capabilities of the HOVER system. With several enhancements to the system (e.g., improved license plate recognition and “whitelist” license plate database), the HOVER system could be used to perform enforcement screening, in which a technician reviewing vehicle compartment images works with a downstream police officer. Significant enhancements to the system (e.g., high-quality video cameras and additional camera views, improved video signal transmission, and improved license plate capture and recognition) could enable its use for HOV ticket-by-mail programs, although enabling legislation for such programs does not currently exist in Texas. The author recommends implementation of these enhancements and further testing to determine future system potential.
Can High-Occupancy/Toll Lanes Encourage Carpooling? Case Study of Carpooling Behavior on the 91 Express Lanes
Authors: Parkany Emily
Published: April 2007

A case study of carpooling behavior on the 91 express lanes is presented. The 91 express lanes are the nation’s first high-occupancy/toll (HOT) lanes on which carpools with three or more passengers could use the lanes for free (at the time the data for this study were collected) and others paid a toll that varied by time of day to use the premium express lane. One concern over such a policy is that people will not carpool if they can just pay for the travel time savings that they would normally obtain by carpooling and using a high-occupancy vehicle (HOV) lane. Survey data show that the rate of carpooling has not changed much since the opening of the express lanes, a lot of changing between modes occurs (increases and decreases in the number of passengers), a large number of people carpool a few times a week, and two-person HOVs use both the regular lanes and the express lanes. It was further investigated whether HOT lanes encourage carpooling by modeling carpool formation with discrete choice models. The results show that mode choice behavior in the corridor is similar to carpooling behavior in other locations, and carpooling in the corridor is not discouraged.
Dynamic Offset Tuning Procedure Using Travel Time Data
Authors: Shoup Gary E. , Bullock Darcy
Published: April 2007

Vehicle reidentification equipment and algorithms are approaching the point at which collection of real-time arterial link travel time data will soon be possible. Such equipment and algorithms will provide a new way for traffic control systems to automatically measure their performance and adapt in real-time to the actual traffic demands on the system. A procedure is described that uses the concept of link travel time data to set offsets off-line for a coordinated actuated arterial signal system. The offset setting procedure is developed in CORSIM and based on recording individual vehicle travel times between coordinated actuated intersections. Establishing offsets in this manner mitigates the “early return to green” problem associated with coordinated actuated systems and accounts for downstream queues that may negatively affect progression. The off-line procedure presented provides the foundation for an on-line algorithm that could adjust offsets based on real-time travel data.
Initial Evaluations of New TRANSYT-7F Version 8.1 Program
Authors: Park Byungkyu , Messer Carroll J. , Urbanik Thomas
Published: April 2007

Recently released TRANSYT-7F version 8.1 was found to provide significant feature improvements such as multiple-cycle simulation, spillback effects, and optimization for oversaturated conditions. An overview of these new features compared with features of the previous version is presented. A comparison between the new TRANSYT-7F version 8.1 and the previous version 7.2 for oversaturated, closely spaced intersections is based on CORSIM simulations. The comparison results show that the new TRANSYT-7F program outperforms the previous one in terms of average delay, queue time, and throughput for oversaturated conditions, but results for undersaturated conditions were similar. The results indicate the queue-blocking algorithm and multiple-cycle simulation recently added to TRANSYT-7F are essential for traffic signal optimization during oversaturated conditions.