bluuebunny/crossref_metadata_2025 huggingface dataset:
Drivers’ Understanding of Protected-Permitted Left-Turn Signal Displays
Authors: Noyce David A. , Kacir Kent C.
Published: April 2007

A comprehensive assessment of protected–permitted left-turn (PPLT) signal displays was performed considering safety, operational performance, and driver understanding measures. The research focuses on a study of driver understanding of permitted left-turn indications. All currently used PPLT display arrangements and permitted indication combinations were evaluated, including those with flashing red and yellow permitted indications. Driver understanding was evaluated through a computer-based driver survey completed by 2,465 drivers. A total of 73,950 survey responses were received pertaining to the 200 different survey scenarios evaluated. The study results indicate that yellow or red flashing permitted indications may lead to higher levels of driver comprehension. Both the flashing red and yellow permitted indications had a significantly higher correct response rate than did the green ball permitted indication. Drivers over the age of 65 found the flashing ball permitted indications easier to comprehend and responded more quickly with fewer fail critical (turning left without the right-of-way) errors. Higher correct response rates with flashing permitted indications were also found in other important demographic groups, including inexperienced drivers and drivers with limited education.
Driver Behavior at Vehicle Arresting Barriers: Compliance and Violations During the First Year at the McLean Site
Authors: Coleman Fred , Venkataraman Kartik
Published: April 2007

Compliance and violation behavior of drivers at one of three vehicle arresting barriers (VABs) in Illinois is presented. VABs are traffic control and safety devices that function as an impenetrable barrier to highway vehicles at railroad grade crossings on high-speed passenger rail corridors. Driver behavior on approach and at the VABs is analyzed to determine compliance and violation behaviors regarding this new device and related signage and signals. During 1999, the first year of operation, the VABs were in operation less than 50 percent of their scheduled time. This diminished the expected data and definable periods for study of driver behavior. Only one site had sufficient data to initiate a qualitative analysis of compliance and violation rates. The early findings suggest that drivers showed less risk-taking behavior during the initial period of operation and that compliance levels were slightly better than those of other innovative highway-rail safety devices studied in recent years. However, over time, the lengthy advanced flashing light warning time, inconsistent and problematic operating profile, and general driver familiarity appear to have led to system credibility and driver compliance issues with the barrier system.
Geographic Information System-Based Evaluation of Geotechnical Borehole Log Quality
Authors: Deaton Scott L. , Frost J. David , Luna Ronaldo , Parsons Robert L.
Published: April 2007

Although standard procedures and methods are available for many aspects of geotechnical site characterization, the quality of the results of such activities can be highly variable because of a variety of factors, including limitations resulting from the test procedures. For initial projects, the nature of these limitations as well as their likely consequences can be reasonably accommodated; however, subsequent use of the same data in a later study may not have the benefit of this project-specific insight, particularly if the data have been archived in a digital database. Consequently, a technique for quantifying data quality is necessary. A geographical information system (GIS)-based methodology has been developed to allow for the evaluation of borehole log quality as a function of its intended use. The methodology uses a flexible hierarchical model to provide a quantitative measure of quality. The quality of the discrete boreholes distributed across a site can then be analyzed spatially within a GIS to provide a more complete assessment of quality for the entire project. This framework also allows for evaluation of the effect of additional borehole logs at a site and can be used to optimize such planning activities in a virtual environment.
Format for Geotechnical Data Exchange in the United Kingdom
Authors: Toll David G. , Walthall Stephen , Sharma Sunil
Published: April 2007

Because information technology is now a common aspect of geotechnical practice, more emphasis is being placed on electronic storage, manipulation, and retrieval of data. Numerous geotechnical database systems have been developed and are in common use. A major advance in geotechnical data management has been the development of a standard format for interchange of geotechnical and geoenvironmental information developed by the Association of Geotechnical and Geoenvironmental Specialists (AGS) in the United Kingdom. The AGS format defines data groups and fields to ensure reliability and consistency for data transfer; it is now widely used as a means of communicating data between and within companies in the United Kingdom. It has received strong support from all involved, from data producers to data receivers and users and software developers. Further possible advances in geotechnical data processing are also considered, such as national data bases and the use of knowledge-based system technologies.
Real-Time Evaluation of Site Characterization to Direct and Conclude Exploration
Authors: Graettinger Andrew J. , Supriyasilp Thanaporn , Durrans S. Rocky
Published: April 2007

A computationally efficient method to direct and evaluate the sufficiency of site characterization activities associated with roadway construction is demonstrated. The method, reliability-based exploration (RBE), combines three-dimensional subsurface analysis with the uncertainty associated with subsurface data to produce a quantifiable measure of exploration sufficiency, which is directly related to the probability of project success. RBE employs a first-order Taylor series expansion to combine the performance model sensitivity and input data uncertainty to calculate the variance in project performance in real time, which, given enough time and computer resources, could be calculated by conventional Monte Carlo (MC) simulations. The study shows that the Taylor series, together with direct derivative coding (DDC), can generate the performance variance much faster than MC simulations. For the example presented, the Taylor series with DDC calculates results 160 times as fast as MC. The RBE method begins with a previous model of the subsurface that can include engineering judgment. As new information is collected at a site, the prior subsurface model is updated with new site data. The robustness and efficiency of RBE are illustrated with a practical example of exploration associated with two designs of a highway interchange. The case study illustrates the RBE approach by identifying the next location for exploration and evaluating characterization sufficiency. In addition, the effects of different designs on exploration are described. The example shows that design affects surface settlement, location of the next boring, and termination of exploration (number of required borings).
Quality Assessment During Road Formation and Foundation Construction: Use of Falling-Weight Deflectometer and Light Drop Weight
Authors: Livneh Moshe , Goldberg Yair
Published: April 2007

Mechanistic empirical-based specifications, which focus on the mechanical properties of materials, facilitate quantitative evaluations of alternative construction practices and materials such as reclaimed materials. Thus, to represent these mechanical properties, quality-control and-assurance testing would be expected to include stiffness along with density measurements. In two case studies, a falling-weight deflectometer (FWD) was used during the construction of two major interchanges in Israel. FWD testing was found to be very useful in identifying local spots with poor performance, thus enabling execution of the required remedy actions. The two studies also indicated that, for a given feature, both a representative central deflection at the 95 percent reliability level and a coefficient of variability of measured deflections may serve as potential quality-control indicators. The possible use of the German light dropweight (LDW) device for measuring the mechanical properties of the formation of flexible pavements was also examined. Based on the cost per test, rate of testing, and quality of the data, the German LDW can serve as a cost-effective testing device for quality control and assurance during subgrade and capping-layer compaction.
Environmental Deterioration Model for Flexible Pavement Design: An Ontario Example
Authors: Tighe Susan , He Zhiwei , Haas Ralph
Published: April 2007

Traffic loading, environmental conditions, subgrade soil, and construction and maintenance quality are among the factors that influence pavement performance. Environmental conditions can have a particularly significant impact on the performance of low-volume road pavements. It is intended that the Strategic Highway Research Program performancegraded asphalts ensure that an asphalt binder is selected based on in-service pavement conditions. This new system will enable designers in Ontario to account for differences in climatic conditions and traffic loading, which vary between the southern and northern areas of the province and have always posed a challenge to pavement designers. A deflection-based method was originally developed in the 1970s based on the AASHO road test and the Brampton road test. The design system incorporates elastic layer analysis to determine pavement response. It uses cumulative equivalent single-axle loads, subgrade type, and layer thickness to determine the most effective design. The design system has been recently updated and recalibrated to separate the environment and traffic effects on performance. In effect, the total pavement performance is the cumulative effect of the damage due to the environment and the damage due to traffic. Hence, the differences between roads in southern and northern Ontario can be quantified. The system calculates roughness either in terms of the international roughness index or the riding comfort index, or in terms of performance as a pavement condition index. The mechanistic-empirical performance model can be recalibrated to apply to conditions outside of Ontario. Examples show the relative deterioration and performance curves for various design situations.
Prediction of Winter Roughness Based on Analysis of Subgrade Soil Variability
Authors: Doré Guy , Flamand Martin , Tighe Susan
Published: April 2007

Frost action is a major cause of pavement deterioration in cold climates. Thermal cracking, differential heaving, and loss of bearing capacity during spring thaw have often been mentioned as the main mechanisms involved. Frost heave observed on pavements built over frost-susceptible subgrades can reach 200 mm in the Canadian climatic context. The problem is mainly because frost heave is rarely uniform. As a result, pavements tend to become rough during winter. Research recently conducted at Laval University in Quebec City, Quebec, Canada, has shown that winter roughness is related to the variability of subgrade-soil properties. A relationship between the variability of soil frost susceptibility and the ratio of winter and summer roughness has been developed. A new approach, based on the relationship, is proposed to help pavement designers to predict and mitigate winter roughness problems.
Evaluating Moisture Sensors and Monitoring Seasonal Moisture Variation in Low-Volume Roads
Authors: Kestler Maureen A. , Hanek Gordon L. , Truebe Mark A.
Published: April 2007

For the past several years, the Forest Service of the U.S. Department of Agriculture has been evaluating a quantitative technique for the application and removal of load restrictions by observing relationships among pavement stiffness, pavement damage, soil moisture, and seasonal freezing and thawing. Laboratory tests of time-domain reflectometry (TDR) and radio frequency (RF) sensors showed them to be reasonably accurate and repeatable when compared with known moisture values in several soil types. Laboratory tests of the probes under repeated adverse freezethaw cycling showed the probes to be durable. Although the field survival rate of TDRs surpassed that of RFs, analysis of field data collected at seven locations in four national forests showed that permanently installed sensors strategically located on a forest road network can provide an affordable method for quantitatively determining the beginning and end of critical periods of pavement weakening associated with springthaw. This information would be useful in administering periods of spring-thaw load restrictions. The laboratory and field test programs conducted are outlined. The field technique is applicable to any secondary road subjected to seasonal freezing.
Influence of Highway Runoff Chemistry, Hydrology, and Residence Time on Nonequilibrium Partitioning of Heavy Metals: Implications for Treatment at the Highway Shoulder
Authors: Glenn Donald W. , Liu Dingfang , Sansalone John J.
Published: April 2007

The control and treatment of highway-pavement storm water at the edge of the highway shoulder pose unique challenges due to the unsteady nature of processes, including rainfall runoff, mobilization and partitioning of heavy metals, variations in storm-water chemistry, residence time on the pavement, and delivery of particulate mass. Presented are heavy-metal partitioning results as influenced by pavement-runoff chemistry and hydrologic parameters from a series of eight rainfall-runoff events over a 2-year period. Water-quality characteristics such as low alkalinity, low hardness, and short pavement residence times cause a majority of the heavy-metal mass to remain in solution at the edge of the pavement, with partitioning coefficients approaching equilibrium conditions only toward the end of the event, as heavy metals partition to entrained solids. There are two primary implications when considering the application of typical best management practices (BMPs) for highway runoff within the right-of-way. The first implication is to use a BMP such as a detention basin or roadside swale to detain runoff and produce sufficient residence time so that partitioning to the entrained solids occurs. The second implication is to use a BMP such as an engineered infiltration trench to provide surface complexation for dissolved metals and filtration mechanisms for the particulate-bound metals. Although no simple solutions exist for the removal of a heavy metal or particle once it is released in the highway environment, knowledge of the dynamic processes in highway runoff can provide insights for the proper selection of BMPs, depending on the conditions at the highway site. A design should be based on the concept that BMPs, to be effective, are essentially garbage cans for heavy metals and solids and as such must be emptied and maintained.
Adsorption and Desorption Capacity of Trichloroethylene on Glacial Till with High-Percent Fines
Authors: Gates Kimberly , Aragona Keith , Sabodish Michael , Gabr M. A.
Published: April 2007

An investigation of trichloroethylene (TCE) mobility in glacial till, as manifested by adsorption and desorption behavior with water, surfactant, and sodium chloride, was conducted. In conjunction with natural attenuation, adsorption and desorption kinetics of surfactant are of interest if other remediation technologies, such as pump and treat, are used. A soil solution ratio of 2:1 with equilibrium times of 48 and 40 h for adsorption and desorption, respectively, was found to produce representative kinetics. The adsorption and desorption partition coefficients for TCE in water are 1.25 mL/g and 11.25 mL/g, respectively. The difference in these values is attributed to the heterogeneous nature of the test soil and hindered diffusion through the intraparticles of the soil and organic matter. Sorption of TCE to glacial till is reduced during adsorption and desorption testing with the use of a surfactant due to a decrease in interfacial tension and an increase in micellar solubilization. However, the effects of surfactant concentrations greater than 4 percent are minimal. The sodium chloride concentration is also varied during testing. As salinity increases, the adsorption and desorption coefficients increase and the solubility potential decreases for the same surfactant concentration. These results are attributed to Winsor Type phase changes that were observed independently of adsorption and desorption testing by varying the amounts of surfactant and sodium chloride with TCE. The methods used and results obtained from the testing program are described, and the mobility of the TCE within the test soil in view of the test parameters is discussed.
Strategic Sustainability Analysis: Broadening Existing Assessment Approaches for Transport Policies
Authors: Schade Wolfgang , Rothengatter Werner
Published: April 2007

Assessment tools based on static and linear concepts such as traditional cost-benefit analysis cannot reasonably be applied for long-term assessments of complex systems. One major reason is that secondary effects of policies caused by endogenous dynamics of the system are not considered. Therefore, the strategic environmental assessment is developed for environmental impacts; it already includes a feedback mechanism—from the failure to reach environmental targets to changes of policy initiatives and to a repeated impact prediction. Because the need to further integrate environmental assessment with economic and social assessment to achieve sustainability is recognized, a so-called strategic sustainability analysis (SSA) is suggested. The SSA is applied for integrated long-term assessment of policies and programs. Requirements and two prototypical examples (Economic Assessment of Sustainability Policies of Transport, Assessment of Transport Strategies) on how to realize SSAs are presented.
Data and Analysis Methods for Metropolitan-Level Environmental Justice Assessment
Authors: Purvis Charles L.
Published: April 2007

An examination is made of data sources and analytical methods available to metropolitan transportation planners for use in technical activities related to environmental justice and Title VI discrimination analyses. The focus is on data and methods employed by the metropolitan planning organization for the San Francisco Bay Area. An initial technical activity is the preparation of a geographic and demographic profile of the region with respect to low-income, minority, elderly, and disabled persons. Difficulties associated with long-range forecasting of these variables at the small area (county) level and very small area (travel analysis zones, neighborhoods) level are discussed. Citizens advisory groups are needed to provide early guidance for this technical activity and to appreciate the uncertainties associated with the data and methods. Transportation analysis procedures to analyze changes in accessibility between alternatives in the long-range regional transportation plan are outlined. These methods map out changes in accessibility to evaluate impacts on transportation disadvantaged versus nondisadvantaged neighborhoods. Future data sources, including Census 2000 and the American Community Survey (ACS), are discussed. The ACS data, in particular, may prove highly beneficial in describing changing socioeconomic patterns within a metropolitan area.
Evaluating Transportation Choice
Authors: Litman Todd
Published: April 2007

Transportation choice refers to the quantity and quality of transportation options available to an individual or group, taking into account varying needs and abilities and including different modes, services, and prices. Transportation choice can provide a variety of benefits, although conventional transportation planning tends to undervalue them and to overlook some transportation options. A more comprehensive range of transportation choice benefits, objectives, and solutions is described and several methods for evaluating transportation choice are discussed. Twenty-five specific transportation options are considered, including various travel modes, substitutes for physical travel, and land use strategies that improve access.
Selection of Noise Barrier Material
Authors: Morgan Susan M. , Kay Dianne H.
Published: April 2007

Because of the large capital expenditures required to construct or replace a noise barrier, it is important for designers to have the information necessary to make rational choices among the materials available. Designers face difficulties, however. There is a lack of information on both existing materials and designs, and many of the new products being introduced are not typical in highway construction. As a result, research was conducted to determine the service life of the various noise barrier materials and products currently in use in Illinois and to develop a life-cycle cost model for evaluating alternative materials. Wood and metal products were estimated to have a 25-year service life; the service life for earth berms, concrete, and fiberglass was estimated to be 50 years. Results of the life-cycle cost analyses (LCCA) indicated that earth berms were the lowest-cost alternative, and metal barriers with absorptive panels were the most expensive. The life-cycle costs of the other barrier materials modeled (including wood, concrete, and proprietary materials) were approximately twice the cost of earth berms. However, although LCCA can provide an additional piece of information in the selection process for noise barrier materials, it should not be used as the sole criterion because of the lack of reliable historical field data on the costs and frequency of maintenance and replacement of barriers.
Performance Evaluation of Recycled and Stabilized Bases in Texas
Authors: Syed Imran M. , Scullion Tom
Published: April 2007

A structural evaluation was performed on 25 base recycling projects in the Bryan District of the Texas Department of Transportation. The recycled layers were stabilized with cement or lime. On higher volume roadways, an unstabilized flexible base was placed over the stabilized layer, followed by a two-course surface treatment. On other pavements, the two-course surface treatment was placed directly on the stabilized layer. Testing was performed using the Dynaflect, falling weight deflectometer, dynamic cone penetrometer, and ground-penetrating radar. A correlation was generated between backcalculated layer moduli and percentage of stabilizer. Tentative moduli values, for thickness designs, were proposed. In the first year, 23 of 25 sections were judged to be performing well, with little or no surface distress. However in the next year, after a severe summer, only 17 were judged to be performing well. The major distress found was severe localized longitudinal cracking, which originated in the subgrade. The shrink-and-swell potential of the subgrade soil appears to be the major factor controlling pavement performance. Sections constructed on soils with a plasticity index of more than 35 did not perform well. The severity of the surface cracking was also related to the following secondary factors: ( a) the summer droughts of 1996 and 1998, ( b) presence of trees near the edge of the pavement, ( c) side slope conditions, and ( d) strength of the stabilized layer. The base recycling technique applied by the Bryan District appears to work well if the subgrade soils have low to moderate plasticity indices. This technique is not recommended for sections constructed on high plasticity index subgrades.
Ultrasonic Testing for Evaluation of Stabilized Mixtures
Authors: Yesiller Nazli , Hanson James L. , Rener Andrew T. , Usmen Mumtaz A.
Published: April 2007

Tests were conducted to evaluate the feasibility of using ultrasonic testing for stabilization applications. The ultrasonic testing consisted of determining primary-wave (P-wave) velocities of stabilized mixtures. The ultrasonic method involves a simple and fast test procedure that allows for repeated assessment of a sample over time. For the testing program, tests were conducted on a high plasticity clay stabilized with lime, cement, and fly ash and a Type F fly ash stabilized with lime and cement. Compaction characteristics of the mixtures were determined using modified Proctor tests. Unconfined compression tests were used to determine compressive strength and modulus of the mixtures immediately after sample preparation and after 7-day and 28-day curing periods. Ultrasonic tests were conducted on the compaction and compression test samples, and the test results were correlated. Variation of velocity with water content demonstrated a similar trend to the variation of dry density with water content for the soil. The velocity increased with increasing density for both soil and fly ash. For compression characteristics, velocity increased with increasing modulus for both soil and fly ash. The velocity correlated well with the unconfined compressive strength of fly ash samples. However, this trend was not as well defined for the soil. Overall, the test program demonstrated that ultrasonic testing can be used effectively to evaluate stabilized materials. P-wave velocity correlations can be used to verify the quality of field placement of stabilized mixtures and to improve mixture design procedures.
Mechanisms of Soil Stabilization with Liquid Ionic Stabilizer
Authors: Katz Lynn E. , Rauch Alan F. , Liljestrand Howard M. , Harmon Jacqueline S. , Shaw Kristine S. , Albers Harold
Published: April 2007

Numerous commercial suppliers are marketing liquid chemical products for stabilizing pavement subgrade and base soils. These nontraditional chemical stabilizers may offer viable alternatives for stabilizing sulfate-rich soils where conventional lime or cement treatment can lead to excessive soil expansion. Typically sold as concentrated liquids that are diluted in water before application, these products may be less expensive to use than lime or cement. However, many transportation agencies are hesitant to specify nontraditional liquid stabilizers without better information on the stabilizing mechanisms and documented field experiences. To identify the mechanisms associated with one class of these products, a representative ionic soil stabilizer and a sodium montmorillonite clay were selected for a detailed physical-chemical study. Laboratory testing included chromatography, spectroscopy, X-ray diffraction, electron microscopy, and standard titration analyses. These tests have shown that the principal active constituents of the selected ionic stabilizer are d-limonene (a by-product of citrus processing) and sulfuric acid, which react to form a concentrated, low-pH solution of sulfonated limonene. The observed changes in clay chemistry following treatment indicated that this product would stabilize a soil by altering the clay lattice. The result is the formation of a more highly weathered, less-expansive clay structure. On the basis of this understanding of the underlying mechanisms, ionic stabilizers applied at sufficiently high application mass ratios may improve the properties of certain soils on some highway construction projects.
Design and Installation of Horizontal Wick Drains for Landslide Stabilization
Authors: Santi Paul M. , Dale Elifrits C. , Liljegren James A.
Published: April 2007

One of the most effective options to stabilize landslides is to reduce the amount of water they contain by installing horizontal drains. A new type of horizontal drain material, geosynthetic wick drains, and a new installation method, driving drains rather than drilling them, were evaluated. Horizontal wick drains offer several advantages over conventional horizontal drains: They resist clogging, are inexpensive, may be deformed without rupture, and may be installed by unskilled laborers with a minimal investment in equipment. More than 100 drains were installed at eight sites in Missouri, Colorado, and Indiana using bulldozers, backhoes, and standard wick drain-driving cranes. Drains have been driven 30 m through materials with standard penetration test values as high as 28. Both experience and research indicate that drains should be installed in clusters that fan outward, aiming for average spacing of 8 m for typical clayey soils. As with drilled drains, initially some drains are expected to be dry, although these drains often become active during wet periods and serve as an important part of the overall slope stabilization scheme. Drain effectiveness is expected to build over the first few years as the effects of soil smear during drain installation are removed, peaking at 3 to 6 years after installation. The effectiveness is then expected to decrease as fine particles slowly clog the drain pores. From published tests, clogging appears to occur slowly enough in typical clay soils that the drain life is comparable with the project life.
Permanent Deformation Behavior of Granular Materials and the Shakedown Concept
Authors: Werkmeister Sabine , Dawson Andrew R. , Wellner Frohmut
Published: April 2007

The shakedown concept has been used to describe the behavior of conventional engineering structures under repeated cyclic loading. The possibility has been raised that a critical stress level exists between stable and unstable conditions in pavement. According to the “shakedown” concept, this level is termed the “shakedown limit.” Several repeated load triaxial tests were performed on crushed rock aggregates at different stress levels. The resulting permanent deformation, which accumulated with the repeated loading, was described and compared with the types of responses usually described by the shakedown approach. The existing shakedown approach can describe some, but not all, of the observed responses. Thus, a modified set of possible responses was defined in shakedown terms. The method of description could provide a powerful material assessment and pavement design tool for engineering unbound pavement bases. A design chart derived from the data illustrates a possible design approach.
Characterizing Alkali-Silica Reactivity of Aggregates Using ASTM C 1293, ASTM C 1260, and Their Modifications
Authors: Touma Wissam E. , Fowler David W. , Carrasquillo Ramon L. , Folliard Kevin J. , Nelson Norman R.
Published: April 2007

Identifying the susceptibility of an aggregate to the alkali-silica reaction (ASR) before using it in concrete is one of the most efficient practices for preventing damage. ASTM C 1260 (Mortar-Bar Test) and ASTM C 1293 (Concrete-Prism Test) have been used to identify ASR-susceptible aggregates. ASTM C 1260 modifications consisted of performing the test using different NaOH solution normalities, namely, 1N, 0.75N, 0.5N, and 0.25N. ASTM C 1293 modifications consisted of increasing the storage temperature from 38°C to 60°C and storing the concrete prisms in 1N NaOH solution at 38°C. The evaluation, comparison, and results for these two tests and their suggested modifications are presented. Data indicate that the levels of test results suggested in the nonmandatory information in the appendix to ASTM C 1260 as “potentially deleterious” are achieved by many aggregates with a good service record. Results suggest that ASTM C 1260 should be used in combination with ASTM C 1293. The nonmandatory information in the appendix to ASTM C 1293 on levels of expansion that should be regarded as potentially deleterious is less likely to be exceeded by aggregates with good service records than in the case of those in the appendix to ASTM C 1260. Changes in the solution normality of the ASTM C 1260 test could be used to evaluate the effect of the alkali content on ASR but do not alleviate the severity of the test for the aggregates investigated. ASTM C 1293 could be effectively accelerated to generate results within 3 months instead of 1 year by increasing the testing temperature from 38°C to 60°C.
Crossover Crashes at Median Strips Equipped with Barriers on a French Motorway Network
Authors: Martin Jean-Louis , Quincy Robert
Published: April 2007

Examination of the accidents in which vehicles cross median barriers on part of the French interurban motorway network shows that the phenomenon is rare. In 7 percent of accidents in which trucks collide with median barriers, the vehicles pass through the barrier versus 0.5 percent for light vehicles. The severity of the accidents in which vehicles go through the barrier is significantly higher than for other types (19 percent fatal versus 1.3 percent). New Jersey–type concrete barriers are crossed in 0.3 percent of accidents involving collisions with median barriers versus 1.3 percent with guardrails, but the number of casualties in crashes involving concrete devices is 1.7 times higher. This increase in severity is not observed if the focus is on serious injuries and fatalities. Some ideas on reducing the number of median barrier crossings significantly without increasing average median barrier collision accident severity are given with regard to narrow median strips.
Road Safety Effects of Bypasses
Authors: Elvik Rune , Amundsen Finn Harald , Hofset Frode
Published: April 2007

The results of a study on the effects on injury accidents of 20 bypass road projects in Norway are reported. Effects were evaluated by means of an observational before-and-after study, controlling for the regression-to-the-mean effect and general areawide trends in the number of accidents. On the average, a statistically significant reduction of 19 percent in the number of injury accidents was found. The two confounding factors controlled in the study did not significantly affect the results. The results of the Norwegian study are consistent with the results of previous studies that evaluated the road safety effects of bypasses. A meta-analysis of 9 evaluation studies, containing a total of 93 estimates of the effects of bypasses, indicated an average reduction of 25 percent in the total number of accidents. Effects did not vary according to accident severity. Note, however, that none of the evaluation studies employed a sufficiently rigorous study design to rule out the possibility that confounding variables not controlled may have influenced the results.
Feasibility of “Subjective” Engineering Assessments of Road Safety Improvements: Bayesian Analysis Development
Authors: Melcher Daniel J. , Dixon Karen K. , Washington Simon , Wu Chi-Hung
Published: April 2007

Regional safety program managers face a daunting challenge in the attempt to reduce deaths, injuries, and economic losses that result from motor vehicle crashes. This difficult mission is complicated by the combination of a large perceived need, small budget, and uncertainty about how effective each proposed countermeasure would be if implemented. A manager can turn to the research record for insight, but the measured effect of a single countermeasure often varies widely from study to study and across jurisdictions. The challenge of converting widespread and conflicting research results into a regionally meaningful conclusion can be addressed by incorporating “subjective” information into a Bayesian analysis framework. Engineering evaluations of crashes provide the subjective input on countermeasure effectiveness in the proposed Bayesian analysis framework. Empirical Bayes approaches are widely used in before-and-after studies and “hot-spot” identification; however, in these cases, the prior information was typically obtained from the data (empirically), not subjective sources. The power and advantages of Bayesian methods for assessing countermeasure effectiveness are presented. Also, an engineering evaluation approach developed at the Georgia Institute of Technology is described. Results are presented from an experiment conducted to assess the repeatability and objectivity of subjective engineering evaluations. In particular, the focus is on the importance, methodology, and feasibility of the subjective engineering evaluation for assessing countermeasures.
Using Human Information Processing Principles to Design Advanced Traveler Information Systems
Authors: Yang C. Y. David , Fricker Jon D.
Published: April 2007

The concepts of human information processing provide design recommendations for advanced traveler information systems (ATISs). A driver’s information processing model for the ATIS environment is proposed. This qualitative model explicitly depicts how drivers process ATIS information, from the moment it is received until a decision is made in response to the information. The model is supported by data collected with a driving simulator. The results of the driving simulator study indicate that, because of the limitations of human memory, drivers prefer to have short, simple ATIS information conveyed to them whenever the circumstance allows. Furthermore, drivers do not always need or want visually displayed information (e.g., an electronic map) to assist them in route navigation. In unfamiliar traffic networks, a motorist’s propensity to change routes is strongly correlated to the quality of ATIS information being processed. With the right amount of traffic information presented using an effective conveyance method, more drivers are likely to accept and use ATIS information and divert to alternate routes. The challenge for ATIS designers is to provide options that are acceptable to ATIS users.
Trip Time Analyzers: Key to Transit Service Quality
Authors: Muller Theo H.J. , Furth Peter G.
Published: April 2007

A trip time analyzer is a system for the offline gathering and analysis of transit operations data. The analyzer consists of a location system; an onboard computer that logs events such as doors opening and closing, stamping each event with time and location data; software that interprets the event logs to reconstruct vehicle trajectories; and a database for storing and analyzing historical data. For virtually all trips, a trip time analyzer provides data on running time by segment, schedule and headway deviation by time point, and delay by segment. Providing a high-quality operation requires these types of data. The benefits and capabilities of trip time analyzers are described, using examples from the Trip Time Analysis in Public Transport system in use in Eindhoven, the Netherlands. Those benefits include monitoring operational quality; improving the schedule; diagnosing operational problems and evaluating countermeasures; and supporting operators, the implementation of priority at traffic signals, and research and innovation in operations management. Trip time analyzers are distinct from, but can share many components with, automatic vehicle location systems and automatic passenger counters.
Designing Synchronization into Bus Timetables
Authors: Ceder Avishai , Tal Ofer
Published: April 2007

The problem of designing efficient bus synchronization into a timetable is addressed. Synchronization means a fit between the arrival time of one bus to the departure time of another bus, so that passengers can transfer from one bus to another. Synchronization is the most difficult task of transit schedulers and is addressed intuitively. The scheduler, in fact, attempts to create the departure times in the timetable while complying with the required frequency, efficient assignment of trips to a single bus chain, and synchronization of certain arrivals. Efficient procedures are presented for applying maximum synchronization as a useful tool for the scheduler in creating timetables. These procedures attempt to maximize the number of simultaneous bus arrivals at the connection (transfer) points of the bus network. Accounting for user satisfaction and convenience, transit schedulers appreciate the importance of creating a timetable with maximum synchronization, which enables the transfer of passengers from one route to another with minimum wait time at transfer nodes. Efficient procedures are described to create the maximum, simultaneous bus arrivals, and a series of examples is presented to illustrate the procedures.
Refinement and Use of Service Standards at the San Diego Metropolitan Transit Development Board
Authors: Williamson Jennifer , Boyle Daniel
Published: April 2007

The San Diego Metropolitan Transit Development Board (MTDB) has established service standards to evaluate the performance of existing routes. The first formalized process for service evaluation was developed in 1993 and approved by the MTDB as Policy 43—Service Management Process. In 1999, MTDB revised and updated the policy to provide for a more objective set of procedures to evaluate existing services and to rank new ones. Proposed changes to MTDB’s current standards and the process of gaining board approval for the new Policy 43 are described. A review of evaluation procedures at similar transit agencies is included. Unresolved issues that MTDB will be addressing over the next year in continuing to refine its service guidelines are briefly described.
Successful Arterial Street Limited-Stop Express Bus Service in Chicago
Authors: Conlon Morgan T. , Foote Peter J. , O’Malley Kevin B. , Stuart Darwin G.
Published: April 2007

The experimental Chicago Transit Authority Route X49 is discussed. After this route was introduced in December 1998, average weekday bus ridership on Western Avenue increased by 17 percent. Customer satisfaction and loyalty measures, as measured by before-and-after customer satisfaction surveys, also increased significantly for both local and express customers (Route 49 before, n = 1,178; Route 49 after, n = 1,006; Route X49 after, n = 730). X49 customer satisfaction mean scores for five (of nine) individual service attributes in the after survey met or exceeded the standard target mean score of 4 (out of a total 5 points)—travel time (4.17), safety at the bus stop (4.09), safety on the bus (4.07), route dependability (4.01), and driver courtesy (4.00). Information provided at the bus stop rated 3.98, narrowly missing the target score. Although nearly all scores for local service attributes improved, none reached 4. A customer loyalty index was developed, based on overall satisfaction ratings, likelihood of continued riding, and willingness to recommend the route to others. X49 customer loyalty nearly doubled, from 21 to 38 percent of respondents assigning the highest rating of 5 points to each of the three components. A review is presented of the travel characteristics (trip purpose, trip length) of survey respondents, overall service productivity of the express and local routes, and future route improvement plans. Conclusions are drawn that reflect the bus service improvement issues and objectives of the FTA Bus Rapid Transit Program.
Accessible Raleigh Transportation: A Paratransit System Using Trip-by-Trip Eligibility Determination and Two-Tiered, User-Side Subsidy
Authors: Olason Robert Alan
Published: April 2007

Accessible Raleigh Transportation (ART), a local, ordinance-based, complementary paratransit service, provides subsidized service for those unable to drive because of a disability and those unable to ride a bus. ART relies on Raleigh’s open-door taxicab licensing policy established by city ordinance. No contract is required to manage the program or operate the service. ART has successfully provided paratransit service for more than 10 years in a fast-growing, highly suburbanized city of 280,000. ART’s Americans with Disabilities Act paratransit element, Tier II, adheres strictly to trip-by-trip eligibility using a functional screening tool. The use of eligibility determination and the user-side subsidy points to a new direction for public transportation.
Potential Effects of Next-Day Reservation Policies on Users of Americans with Disabilities Act Paratransit Systems
Authors: Venter Christoffel J.
Published: April 2007

The Americans with Disabilities Act (ADA) of 1990 significantly improved the mobility of physically disabled persons. However, one component of the ADA regulation has potentially adverse effects on users—namely, reservation policies. ADA allows operators to restrict paratransit trips to those reserved 1 day or more in advance. The effects of next-day reservation policies are addressed with regard to the number and types of potentially affected activities and users. The research sought a basic understanding of the fundamental behavior of activity planning, using qualitative and quantitative approaches. An exploratory study was conducted to identify the factors affecting the amount of advance planning—or planning lead time—people take before engaging in activities and travel. An empirical model was calibrated on a unique data set from Windham, Connecticut. The model confirmed that longer lead times are associated with certain activity types, as well as the travel needs and personal characteristics of the activity participant. The model was applied to a pre-ADA sample of disabled persons from the San Francisco Bay Area to estimate the effects of a next-day reservation policy on their current activity behavior. The results show that only a small fraction of activities and users are likely to be negatively affected, because of the tendency of this population to plan many activities long in advance for other reasons. However, the constraints imposed on those who are affected may be severe because these persons include the least mobile part of the population and have the greatest need for short-notice transport, for instance, in requiring urgent medical care.
Improving Transit Service Quality and Headway Regularity with Real-Time Control
Authors: Ding Yuqing , Chien Steven I.
Published: April 2007

Disrupted transit operations are often caused by stochastic variations of passenger demand at stations and traffic conditions on service routes, which increase passenger wait times and thus discourage passengers from using the transit system. Efficient, real-time operational control is desirable to maintain headway regularity and reduce the negative effects of service disturbance. A real-time headway control model is proposed to maintain desired headways for pairs of successive vehicles by minimizing total headway variance for all stations in an advanced public transportation system environment, such as an automatic train control system and an automatic vehicle location system. A vehicle’s departure time can be adjusted on the basis of its optimal arrival time at the next station, while considering the maximum attainable operating speeds and the headways to its leading and following vehicles. The proposed real-time control model is tested by simulating a high-frequency light rail transit route in Newark, New Jersey. The simulation results demonstrate that the average passenger wait time is significantly reduced after applying the control model.