bluuebunny/crossref_metadata_2025 huggingface dataset:
Iterative Design and Implementation: A Model of Successful Scheduled Maintenance Technology Deployment
Authors: Chamberlain E. Sterling , Di Bello Lia A.
Published: April 2007

With significant budget reductions, many transit providers are finding that they must examine the way in which they maintain their fleets. As the use of outsourcing to stay within budget increases, those serious about maintaining their own fleets are looking more closely at totally new approaches that emphasize the efficient use of funds and labor resources with the goal of maintaining high fleet performance. Preventive maintenance has been accepted as a solution, and many transit industries are investigating computerized decision support systems (DSSs), often borrowing technologies developed for related industries (e.g., aviation) and tailoring them for transit purposes. Unfortunately, most implementations fall short of expectations. To be effective, DSSs require users with an in-depth understanding of their logic and detailed knowledge of the work being done. Mechanics and foremen have the work knowledge but are unlikely to possess an understanding of computerization and the abstract algorithms driving these technologies. One system adapted to the transit industry by New York City Transit—MIDAS—has been implemented successfully in the Department of Buses. The three-part top-down/bottom-up model for technology deployment is described, as is the evaluation used to measure its success: a relatively small design team of software developers, maintenance managers, shop-floor workers, and foremen; a powerful new training technique resulting in direct data entry from the shop floor; and feedback from the work floor to tailor the system. It is concluded that deployment must be organized around the concept that DSSs are tools appropriated by the users and that implementation efforts should facilitate that process. This is in striking contrast to “turnkey” approaches. Follow-up evaluation data are presented that show how this model leads to more innovative and effective system use over time.
PART 2: Paratransit: Paratransit Customer: Modeling Elements of Satisfaction with Service
Authors: Wallace Richard R.
Published: April 2007

Because of the arrival of advanced public transportation systems (APTS) and other changes in the transit environment, the study of the paratransit customer deserves increased attention. Demographic and other characteristics of paratransit customers in southeastern Michigan are presented, and the development of a causal model of the factors affecting customer satisfaction with paratransit service is begun. Such models, which analyze the covariance structures of variables and factors hypothesized to exhibit causal relations, can help researchers and transit operators gauge the potential of improving customer satisfaction through system changes, such as the addition of APTS. Furthermore, these models can suggest which elements of customer satisfaction are most affected by specific system changes. A key finding from the modeling effort is that characteristics specific to the customers, such as personal mobility, contribute substantially toward explaining customer satisfaction. The causal modeling also revealed that transit system characteristics contribute substantially to customer satisfaction, too, especially to customer satisfaction with the trip reservation process. Thus, system enhancements, such as APTS, have ample potential to increase customer satisfaction. Finally, directions for future research aimed at improving and enhancing the developed causal model are discussed and recommended, including specification of the data needs of such research.
Forecasting Demand for Paratransit Required by the Americans with Disabilities Act
Authors: Koffman David , Lewis David
Published: April 2007

Four techniques are described for forecasting the demand for paratransit required by the Americans with Disabilities Act (ADA): surveys, intuitive comparison with other systems, cross-sectional econometric analysis, and time-series econometric analysis. The application of these methods in Seattle and New York is described, illustrating the advantages and disadvantages of each method. The ADA leaves considerable room for localities to determine the level of trip denials that can be tolerated. The econometric models provide a quantitative forecast of the effects of different levels of service availability as measured by trip denial rates. It demonstrates that the importance of service availability varies among communities.
Performance Impacts of Operating Subsidies in the Paratransit Sector
Authors: Karlaftis Matthew G. , Sinha Kumares C.
Published: April 2007

A multitude of studies in recent years have concluded that there are clear links between the amount of government subsidies and subsequent levels of transit performance and productivity. These studies have used data from fixed-schedule/fixed-route transit systems, largely ignoring the possibility of a different reaction of paratransit systems to the provision of operating subsidies. The effect of operating subsidies on the performance of paratransit systems is examined. The results indicate that subsidies from different sources (federal or state and local) have different directions and magnitudes of effects on the performance of different types of paratransit systems. Privately operated systems have been able to absorb and utilize subsidies in such a manner that has increased their performance, but the performance of publicly operated systems has generally decreased with the provision of subsidies. Finally, a drastic reduction in the levels of federal operating subsidies, a direction toward which the government is heading, will significantly and negatively affect the performance of paratransit systems.
Cost and Productivity Impacts of a “Smart” Paratransit System
Authors: Chira-Chavala T. , Venter Christoffel
Published: April 2007

The cost and productivity impacts of an advanced paratransit system are analyzed; the system uses a digital geographical data base and an automated trip scheduling system to automate vehicle and passenger scheduling functions. The results indicate that such a system enables transit agencies to accommodate rapid increases in the paratransit demand in an efficient manner, which could not be accomplished by a manual or semimanual scheduling system. For the case study presented, this new system resulted in 13 percent savings in unit transportation operating cost and a significant increase in the percentage of shared rides. These benefits were achieved without affecting passengers’ travel time or ride comfort.
Americans with Disabilities Act, Paratransit, and Dialysis
Authors: Denson Carol R.
Published: April 2007

In transportation, a potential conflict exists between the needs of people who are dependent on kidney dialysis to support life and the mandates of the Americans with Disabilities Act of 1990 (ADA), which protects the civil rights of people who are disabled. To address this conflict, baseline information about existing transportation patterns for people on dialysis treatment was established. An original survey questionnaire was administered in person, by trained interviewers, to 289 recipients of dialysis treatments in Delaware. The questions focused on critical transportation issues and were designed to obtain information about transportation user patterns to and from dialysis treatments; transportation modes used to and from dialysis treatments; points of origin and destination; length of trip in distance and time; the way transportation arrangements are made, by whom, and at what cost; and alternative public transportation modes that dialysis riders would be willing to use. Social demographic characteristic questions were also included. Although the understanding of mobility patterns and modes of transportation employed by dialysis users has been increased, the supposition that ADA has created problems directly for dialysis recipients in transportation is not substantiated. Before this research, however, no empirical information was available.
PART 3: Intermodal: Integrated Timed Transfer: A European Perspective
Authors: Clever Reinhard
Published: April 2007

Integrated timed-transfer (ITT) systems are starting up in Switzerland, Austria, and many regions of Germany. They distinguish themselves from regular timed-transfer systems, in which vehicles arrive at and depart from a station at approximately the same time to minimize waiting times for passengers, by integrating the timed-transfer systems of individual metropolitan areas into one complete public transportation system for a region. Very little has been written about ITT in the English language literature, and the purpose here is to close the information gap. The advantages and disadvantages of an ITT system are illustrated by discussing a concrete example. Technical and economic aspects of ITT are discussed. Terms such as “symmetry time” and “optimal minimum headway” are defined. Early results of ITT systems in Europe are reported. The applicability of ITT to North America is demonstrated with the example of the San Jose–Oakland–Sacramento corridor. The public transportation system in this area is currently disjointed, and the introduction of ITT would increase the usability of public transit.
Diesel Light Rail Transit: Niche Description and Rating System
Authors: Sullivan Brian E.
Published: April 2007

The appearance of a new rail car technology, combining the features of the latest in low-floor streetcar design with those of diesel freight railways, makes it possible to consider rail service for passenger flows much lower than generally have been found feasible until now. With the introduction of any new technology comes the question, What is its role? It is concluded that the provision of short-haul services—within inner and outer suburbs, and between such places and downtowns—is where the greatest potential lies. Additional applications are ( a) similar services extending beyond the commutershed into the trading hinterland of a city, ( b) those catering to cross-radial travel within a central city or region that is not oriented to downtown, and ( c) those that may sometimes involve a nonurban region or tourism. This could be a significant development, as much of the U.S. and Canadian population lives in low-density suburbs or semirural counties, both of which can be expected to continue their dominance of the growth agenda. One of the advantages of this new family of diesel light rail technology arises from its ability to use existing pathways through cities and towns. This keeps costs low and avoids the dislocation and environmental problems associated with the taking of large swaths of land required by many solutions. One way to do this is by using existing railway tracks or rights of way. Another is to share right-of-way space with a road, either in a streetcar format or on a separate strip. The results have proven useful in an assessment of freight railway lines in Calgary and Edmonton with respect to their potential for diesel light rail services.
Rail Transit in the Suburbs: Case Study of Transit Use in Atlanta’s Affluent Northern Tier
Authors: Nelson Arthur C. , Sanchez Thomas L. , Ross Catherine L. , Meyer Michael D.
Published: April 2007

The conventional view of public transit is that it serves the mobility needs primarily of poor, mostly inner-city residents. In 1979 the Metropolitan Atlanta Rapid Transit Authority (MARTA) opened rail service connecting inner-city neighborhoods to downtown. By the mid-1990s, rail service had been extended south to Atlanta’s international airport, east and west to Interstate 285 (Atlanta’s perimeter freeway), and north into the region’s affluent, mostly white suburbs. Research into how MARTA’s rail system has influenced travel behavior among affluent “northern-tier” suburbanites is reported. Four major findings are offered. First, in those corridors where rail transit is provided, mode choice among commuters has shifted measurably from the single-occupant vehicle to transit. Second, the opening of rail stations in suburban areas is shown to reduce vehicular traffic on nearby surface streets, further suggesting rail’s influence on travel behavior in the suburbs. Third, rail transit is found to attract affluent, white, male commuters who are willing to ( a) travel longer distances to access rail and ( b) travel longer distances on rail than the general population of rail patrons. Fourth, transit riders appear to be more sensitive to transit service than to fare increases—that is, as the rail system expands, ridership among suburbanites increases regardless of changes in fare. The overall picture that emerges is that affluent suburban communities respond favorably to rail transit. This leads to a set of policy implications that transcend Atlanta’s experience.
Achieving Suburban Transit Potential: Sacramento Revisited
Authors: Thompson Gregory L.
Published: April 2007

The research examines whether fixed-route transit can serve intrasuburban travel demand. With a direct demand model estimated with travel survey data from Sacramento, California, potential transit demand to destinations in suburbs is estimated, and the link from suburban areas of heavy demand to areas with relatively high demand for beginning trips is assessed. Next, a transit service improvement scenario is simulated to test the sensitivity of suburban transit accessibility to service change based on rail transit with timed-transfer bus connections. It is found that the existing system already carries more passengers within the suburbs than from the suburbs to downtown. Suburbs account for almost 60 percent of potential transit demand in the region, and there is potential for tapping more of it. Finally, typical transit improvements can substantially improve accessibility to potential suburban transit destinations from potential transit origins.
NJ Transit’s Rail Coach Purchase: Letting the Customers Choose
Authors: Pepper Janice , Ray Ana
Published: April 2007

NJ Transit was planning to purchase 95 new rail cars to be delivered in October 1996. These cars would replace 70 older cars that will be retired, thus adding 25 new cars to the existing fleet of 715 cars to accommodate expanded service. Before purchasing the new cars, NJ Transit conducted qualitative and quantitative research to test customer satisfaction with the interior features of a new proposed rail coach and to identify customers’ preferences regarding seating configuration. The first phase of the research consisted of four focus groups with NJ Transit employees and customers. Customers were asked to rate interior features of current coaches such as colors, doors, public address system, leg room, and seating configuration. Next, customers were asked to rate interior features of a new proposed coach on the basis of a pictorial design concept. The second phase entailed a quantitative research study. A questionnaire was designed to collect and analyze rail passengers’ seating patterns, preferences, and input into the “3-2” or “2-2” seating configuration decision. The questionnaire was also designed to capture market segmentation of opinion and to compare current seating behavior patterns with stated preferences and opinions. The results of the research were used to design a visually appealing, durable, and maintainable interior that incorporates customers’ preferences regarding colors, textures, and seating configurations for the 95 rail coaches that will go into revenue service in October 1996.
Public Decision Making for the CalTrain Downtown San Francisco Extension Project
Authors: Nash Andrew Butler
Published: April 2007

The public input process used to refine alternatives being considered for extending commuter rail service to a new station in downtown San Francisco is described. At the study’s outset there were two major build alternatives with numerous design options. Through the “design options screening” process, the number of build alternatives was reduced to one and the number of design options was reduced significantly. Reducing the scope of the study enabled resources to be focused on addressing the remaining critical questions in development of the draft environmental impact statement. The design options screening process consists of breaking the options into a series of questions, providing detailed information about each of the questions, and encouraging the public to weigh in on the questions. The process was very successful at focusing public involvement and in allowing the policy board to make decisions.
Rail in Multimodal Transit Systems: Concept for Improving Urban Mobility by Increasing Choices for Travel and Lifestyle
Authors: Schumann John W.
Published: April 2007

Metro areas relying on automobile-based transport are increasingly congested. Some alternatives to gridlock are being implemented; others languish without political acceptance. Congestion is more than a suburban issue. Both intersuburban and radial travel woes are growing and must be addressed. Agencies should start with bus improvements, then add rail where appropriate. Experience shows that, unlike purely radial systems, transit networks with many transfer opportunities offer options to users in more travel markets and, as a result, attract more riders. In the United States, rail is often viewed as serving just the central business district (CBD) and being incapable of accommodating suburban trips. In fact, radial rail lines can provide attractive options for trips to new centers near suburban rail stations, in addition to CBD trips. Rail systems become regional connections, linked via timed transfers at transit centers with bus and paratransit feeders and circulators. Clock headways and integrated fares complete a seamless multimodal, multidestinational system serving the CBD as well as emerging regional centers. Such systems work best as part of a comprehensive program for sustainable urban development, consciously planned by committed, far-sighted political leaders who build public consensus to implement a regional vision for community patterns that encourage a rich variety of lifestyle and mobility choices. Key to effecting such transport systems are ( a) competent transit management that seeks out and serves a variety of niche markets, and ( b) coordinated transportation and land use decision making that values transit links to major destinations and compact communities.
Intersection Delay in Regionwide Traffic Assignment: Implications of 1994 Update of the Highway Capacity Manual
Authors: Horowitz Alan J.
Published: April 2007

The original 1985 Highway Capacity Manual (HCM85) described widely recognized relationships for traffic delay that could be incorporated into travel forecasts. Applications of the HCM85 procedures demonstrated that such delay relationships were both technically feasible and beneficial. In early 1995, the Transportation Research Board released the 1994 update to the HCM (HCM94), heavily revising the signalized and two-way stop intersection procedures and introducing a detailed all-way stop intersection procedure. These new procedures have the potential to improve the accuracy of forecasts and to make forecasts consistent with other design practices. Implementation of the HCM94 procedures into travel forecasts reveals that fewer adjustments are required to make them work within equilibrium traffic assignments. The two-way stop procedure can be used nearly intact. The signalized intersection procedure, although still requiring some adjustments, allows a greater range of traffic conditions and phasing options. The all-way stop procedure cannot be incorporated into travel forecasts because of its restrictions on allowable volumes and turning movements. Tests of the HCM94 procedures in traffic assignments indicate that they produce noticeably different results (both volumes and link delays) than the original HCM85 procedures. Multiple equilibrium solutions are possible, but the differences between these solutions are small and manageable.
Development of Guidelines Based on Life-Cycle Cost To Replace Level-of-Service Concept in Capacity Analysis
Authors: Bang Karl-L. , Lindberg Gunnar , Harahap Gandhi
Published: April 2007

Highway capacity manuals (HCMs) from developed countries cannot be successfully applied in Indonesia because of significant differences in driver behavior, traffic composition, and level of roadside activities. The Indonesian HCM project (IHCM) was therefore started in 1991 and has resulted in a manual and software for urban traffic facilities, inter-urban roads, and motorways. The IHCM also includes traffic engineering guidelines for selection of appropriate road and intersection type and design for new construction or improvements based on life-cycle cost (LCC) analysis. The LCC model includes all relevant road-user costs (those for vehicle operations, time, accidents, and emissions) and road-producer costs (those for land acquisition, road construction, and road maintenance and operation). The LCC results identify the design alternative that has the lowest total cost and thus is the most economical for any given traffic flow. The IHCM guidelines also include traffic-performance graphs for standard road types and intersections as a function of traffic flow as well as information about accident rates and the impact of geometric design changes on safety. The guidelines assist the user with preliminary selection of the design before starting the detailed analysis. They can also be used on their own as a shortcut for planning purposes and therefore serve as a replacement for the level-of-service concept applied in the U.S. HCM.
Assessment of Roadway Capacity Estimation Methods
Authors: Minderhoud Michiel M. , Botma Hein , Bovy Piet H. L.
Published: April 2007

Capacity is a central concept in roadway design and traffic control. Estimation of empirical capacity values in practical circumstances is not a trivial problem; it is very difficult to define capacity in an unambiguous manner. Empirical capacity estimation for uninterrupted roadway sections has been studied. Headways, traffic volumes, speed, and density are traffic data types used to identify four groups of capacity estimation methods. Aspects such as data requirement, location choice, and observation period were investigated for each method. The principles of the different methods and the mathematical derivation of roadway capacity are studied and discussed. Among the methods studied are the headway distribution approaches, the bimodal distribution method, the selected maxima, and the direct probability method. Of the methods based on traffic volume counts, the product limit method is recommended for practical application because of sound underlying theory. An example of the application of this promising method is presented. Attempts to determine the validity of existing roadway capacity estimation methods were disappointing because of the many ambiguities related to the derived capacity values and distributions. A reliable and meaningful estimation of capacity is not yet possible. Lack of a clear definition of the notion of capacity is the main hindrance in understanding what exactly represents the estimated capacity value or distribution in the various methods. If this deficiency is corrected, promising methods for practical use in traffic engineering are the product limit method, the empirical distribution method, and the well-known fundamental diagram method, in that order. The choice of a particular method strongly depends on the available data.
Analysis and Evaluation of the Capacity of Roundabouts
Authors: Polus Abishai , Shmueli Sitvanit
Published: April 2007

Roundabouts are replacing conventional unsignalized intersections in many parts of the world and could become more widespread in the United States, although there are some limitations as well as clear advantages. Models for entry capacity into the rotary were developed. Entry capacity depends on the geometric characteristics of the roundabout, particularly the diameter of the outside circle of the intersection. The geometric characteristics determine the speed of vehicles around the central island and, therefore, have an impact on the gap-acceptance process and consequently the capacity. Traffic conditions that impede entry capacity involve the flow around the roundabout. Flow and geometric data from six small to medium-sized roundabouts were analyzed. Individual and aggregated entry-capacity models were calibrated by using the diameter and circulating flows as explanatory variables. Very good fits to the data were obtained; the results also fit models developed in other countries. The Australian model resulted in slightly higher entry capacities for moderate to low circulating flows and lower entry capacities for high circulating flows. Very close proximity to the German model was obtained, although it does not depend on the geometric characteristics of the circle. The roundabout provides an advantage over a conventional unsignalized intersection. A faithful concurrence between the model developed and the latest Highway Capacity Manual model for right-turn capacity at an unsignalized intersection is obtained if the circulating flow is replaced by the conflicting flow. The advantage of entry capacities of the roundabout over the calculated capacities of the Highway Capacity Manual left-turn model is shown. Further research is proposed to study the effect on entry capacity of two circulating lanes rather than one and the effect of the increase in circulating flows on the gap-acceptance process, particularly the reduction in critical gap at high flows.
Validation of Generalized Delay Model for Vehicle-Actuated Traffic Signals
Authors: Rouphail Nagui M. , Anwar Mohammad , Fambro Daniel B. , Sloup Paul , Perez Cesar E.
Published: April 2007

One limitation of the Highway Capacity Manual (HCM) model for estimating delay at signalized intersections is its inadequate treatment of vehicle-actuated traffic signals. For example, the current delay model uses a single adjustment for all types of actuated control and is not sensitive to changes in actuated controller settings. The objective in this paper was to use TRAF-NETSIM and field data to evaluate a generalized delay model developed to overcome some of these deficiencies. NETSIM was used to estimate delay at an isolated intersection under actuated control, and the delay values obtained from NETSIM were then compared with those estimated by the generalized delay model. In addition, field data were collected from sites in North Carolina, and delays observed in the field were compared with those estimated by the generalized delay model. The delays estimated by the generalized model were comparable with the delays estimated by NETSIM. The data compared favorably for degrees of saturation of less than 0.8. However, at higher degrees of saturation, the generalized model produced delays that were higher than NETSIM’s. Some possible explanations for this discrepancy are discussed. The delays estimated by the generalized model were comparable with delays observed in the field. Researchers have concluded that the generalized delay model is sensitive to changes in traffic volumes and vehicle-actuated controller settings and that the generalized delay model is much improved over the current HCM model in estimating delay at vehicle-actuated traffic signals.
Using Input-Output Diagram To Determine Spatial and Temporal Extents of a Queue Upstream of a Bottleneck
Authors: Lawson Tim W. , Lovell David J. , Daganzo Carlos F.
Published: April 2007

A simple approach is described for modifying an input-output (or queue-ing) diagram to measure the time and distance spent by vehicles in a queue in a much simpler and self-serving manner than a time-space diagram. The graphic technique requires construction of a curve depicting the cumulative number of vehicles to have reached the back of the queue as a function of time, but, as indicated here, the technique can be easily automated with a spreadsheet. The technique is applied to the simple case of a constant departure rate from a bottleneck and to the slightly more general case of a bottleneck capacity that changes once, which is demonstrated to be applicable to the study of an undersaturated traffic signal. In the course of describing the usefulness of this technique for estimating several measures, including the maximum length of a physical queue and the time when this maximum occurs, the difference between “delay” at a bottleneck and the “time spent in queue,” which appears to have been confused in some of the literature, is clarified.
Performance Measures in Canadian Capacity Guide for Signalized Intersections
Authors: Teply S.
Published: April 2007

The set of performance measures included in the second edition of the Canadian Capacity Guide for Signalized Intersections, an updated, enhanced, and significantly expanded version of a Canadian traffic engineering document, is described. Because some of these measures represent new research applications and have not been published elsewhere, the objectives here are threefold; ( a) to share the results with the broader technical public, ( b) to present them for an international discussion, and ( c) to contribute to the ongoing debate on evaluation of the performance of signalized intersections, often the most critical elements of urban networks. The second edition presents a set of traditional, modified, and new analytical tools as well as a set of up-to-date numerical parameters for Canadian conditions, which make it possible to analyze specific problems and to assess the benefits and disadvantages of alternative solutions. The number of measures of effectiveness has been substantially increased compared with the first edition. In addition to the traditional types of delay, there are two new key performance measures: total person delay and delay to pedestrians. These are essential prerequisites for equitable treatment of all modes of transportation, especially public transit. Other performance measures, such as several types of queues, probability of cycle overload, number of stops, fuel consumption, and pollutant emissions, provide the user with a comprehensive account of intersection operation. Some of these measures are also useful as input to economic and environmental analyses. In addition, the results of the procedures may provide vital information for transportation demand modeling and forecasting.
Utilization of Auxiliary Through Lanes at Signalized Intersections with Downstream Lane Reductions
Authors: Hurley Jamie W.
Published: April 2007

The capacity of multiple through lanes at signalized intersections depends on the distribution of traffic within these lanes, with equal lane distribution corresponding to maximum capacity. However, traffic characteristics, land use, and geometric factors usually prohibit this from occurring. Although the 1994 update of the Highway Capacity Manual considers the case of continuous through lanes at signalized intersections, the default values provided do not address situations in which lane reduction takes place downstream of the intersection. Lane distribution data obtained in the field can remedy the situation but for existing conditions only. This research employed the concept of captive and choice lane users in modeling lane use for intersection configurations with a single continuous through lane and an “auxiliary” through lane, which is continuous upstream of the intersection but is dropped downstream of it. Stepwise multiple regression was performed on data collected at sites in Tennessee to ascertain those factors significantly affecting auxiliary lane use. These factors were found to be ( a) right turns off the facility at the intersection, ( b) total left turns off the facility downstream of the intersection, ( c) right turns onto the facility in the first 122 m (400 ft) upstream of the intersection, ( d) right turns off the facility in the last 152 m (500 ft) of the auxiliary lane, ( e) downstream auxiliary lane length, and ( f) the existence of left-turn bays or two-way continuous left-turn lanes downstream of the intersection. For the configuration studied, lane distribution data often differed considerably from the default values given in the Highway Capacity Manual.
Collision Avoidance Behavior of Unalerted Drivers Using a Front-to-Rear-End Collision Warning Display on the Iowa Driving Simulator
Authors: Lee Jaesik , McGehee Daniel V. , Dingus Thomas A. , Wilson Terry
Published: April 2007

This study investigated whether drivers who operate a vehicle equipped with a front-to-rear-end collision warning system can avoid crashing when a lead vehicle brakes at its maximum potential (e.g., -0.85 g). Drivers in the experimental condition drove a 1993 General Motors Saturn mounted on the Iowa Driving Simulator’s six-degree-of-freedom motion base. The simulator cab was equipped with a collision warning display that provided a primary auditory warning and secondary visual warning based on a time-to-collision algorithm between the subject’s vehicle and the lead vehicle. Two headway distances were tested (2.7 sec and 3.2 sec). The collision avoidance performance of subject drivers was compared to the behavior of drivers in a baseline condition where no collision warning display was present. Relative to the baseline condition, results indicate that drivers using the collision warning display ( a) showed significantly fewer crashes in the shorter headway condition, ( b) collided with the lead vehicle at significantly slower impact speeds, ( c) released the accelerator significantly faster, and ( d) had longer headways both at accelerator release and brake initiation.
Human Factor Studies in Evaluation of Automated Highway System Attributes
Authors: Ran Bin , Leight Shawn , Johnson Seth , Huang Wenjing
Published: April 2007

The goal of the Automated Highway System (AHS) is to blend engineering ingenuity and technology to produce a new level of transportation services. Human factors are difficult to integrate with AHS design because they represent a variety of training, experience, skills, and goals. Human factor considerations are essential for AHS design because humans will be involved in automated driving. For instance, drivers may be expected to instruct their vehicles to exit locations, input parameters such as speed and desired headway, or take control in some emergency situations. The tasks that human drivers will be expected to execute have not yet been fully defined. One human factor dilemma that AHS engineers might face is that if human drivers are not allowed to intervene in the vehicle control process during malfunction and emergency situations, they may be trapped in a system with high failure rates. This could result in public distrust and a lack of public will to deploy an AHS. However, if drivers are allowed to take control of their vehicles at will, some may intervene at inappropriate times, causing a potential system failure. A framework has been developed for evaluating human factor concerns for automated vehicle control. These concerns involve basic driving tasks: ( a) detection, ( b) recognition, ( c) situation analysis, ( d) decision making, and ( e) control response. An analytical process to determine the responsibilities of the human driver, vehicle, and AHS infrastructure for these driving tasks is presented.
Understanding Driver Behavior Through Application of Advanced Technological Systems
Authors: Manser M. P. , Hancock P. A. , Kinney C. A. , Diaz J.
Published: April 2007

The use of the unecological removal research scenario in recent years has been forced because of technological limitations. However, with the advent of three-dimensional modeling programs and high-fidelity graphic systems, the ability to accurately represent real-world situations in computer-generated worlds has become easier, cheaper, and more realistic. A time-to-contact (TTC) experiment is reported in which the manner of removing an approaching vehicle from the environment was manipulated. One scenario, the disappearance condition, featured a traditional, instantaneous removal of a vehicle. The purpose of this research was to determine if a more ecological research scenario, one in which the approaching vehicle becomes occluded by a naturally occurring object (the occlusion condition), influences a driver’s ability to estimate TTC accurately. The available visual information was essentially equivalent in both scenarios. If the level of ecological validity has no effect on estimates of TTC, estimates of TTC between the two scenarios would be expected to be similar. Results, however, showed estimates with 14 percent greater accuracy in the occlusion condition compared with the disappearance condition, implying that researchers have been using a research scenario that biases estimates of TTC. Further, the results of the present findings imply that there are processes that occur in real world settings that have not being accounted for in previous TTC research.
Intersection Design and Decision–Reaction Time for Older Drivers
Authors: Naylor David W. , Graham Johnny R.
Published: April 2007

Trends in automobile and roadway use have changed drastically over the past several years. Changes in the trends include an increase in the percentage of licensed drivers, annual miles driven, and an increase in the number of older drivers. Of particular concern is the increase in the number of older drivers and the question of whether the current design standards adequately meet the needs of the older driver. In this study, the perception-reaction time variable used in calculating intersection sight distance at stop sign-controlled intersections was evaluated. The current design value for the perception–reaction time is 2.0 sec, which has been used since the 1940s when the driving population was much younger. A field experiment was performed to determine an appropriate value for today’s driving population. Subjects were covertly videotaped as they entered two rural and two urban stop sign-controlled interactions. Mean decision–reaction times were determined for an older and a younger group of subjects. The older group, consisting of 104 subjects, averaged 69.3 years of age and had a mean decision–reaction time of 1.32 sec. A group of 104 younger subjects, less than 30 years of age, had a mean decision–reaction time of 1.24 sec. The 85th percentile decision–reaction time for the older group was 1.86 sec and for the younger group, 1.66 sec. Both times were less than the current AASHTO design value of 2.0 sec.
Mobility Patterns of the Next Generation of Older Persons
Authors: Zhou Min , Lyles Richard W.
Published: April 2007

Mobility patterns of the next generation of older people may be significantly different from today’s older persons. And it is likely that more older people may depend on automobiles for their daily activities. While the types of traffic safety-related problems associated with older drivers are fairly well defined, the questions that remain are about the magnitude: Will large numbers of older drivers self-test off the system? or Will many more older persons driving more often and longer distances produce even more serious safety-related problems? Differences between mobility patterns of today’s older people and those predicted for the next generation of older people are examined. The overall finding is that as the older population continues to shift to rural areas, small cities, and suburbs, there is likely to be increased per capita travel (i.e., higher exposure), even though the number of trips may be lower. It seems likely that a considerable percentage of this travel will be on the least safe parts of the highway system (i.e., local streets and roads). Although overall accident rates may remain much the same or drop slightly for the older person, the greater number of persons in the older-age cohorts and the increased mileage driven by them will likely lead to significant increases in the number of accidents experienced by this group and in general.
Shoulder Rumble Strip Effectiveness: Drift-Off-Road Accident Reductions on the Pennsylvania Turnpike
Authors: Hickey John J.
Published: April 2007

To help decrease the number of accidents caused by drowsy drivers, engineers for the Pennsylvania Turnpike developed, and installed on the highway shoulder, an innovative rumble-strip called the Sonic Nap Alert Pattern (SNAP). A distinct warning sound and vibration are produced when tires roll on the strips. When drowsy or inattentive drivers’ vehicles drift to the right, the tires cross this pattern of recessed grooves along the shoulder of the roadway. Various lengths and depths of grooves were tested to select a design with enough sound and vibration to be perceptible in a truck cab and yet not too severe for cars or motorcycles. Design features, testing, and initial results were presented at the TRB Annual Meeting in January 1994. After installation of SNAP, drift-off-road accidents per month decreased by 70 percent. This study reviews those initial results, adds traffic exposure to compare accident rates per vehicle-distance-traveled, adjusts for a decline in all accidents during the years considered, and revises the initially reported accident reduction to 65 percent. Follow-on results are developed for all reportable accidents from 1990 to 1995, singling out those that could be directly affected by SNAP. About 12 percent of all accidents were considered fully susceptible to SNAP treatment. A reduction of 60 percent in treatable accidents, or a decline in rate by 1.43 per 100 million vehicle kilometers, (2.3 accidents per 100 million vehicle miles) was documented for 53 segments totaling 560 km (348 mi) of roadway.
Effect of Superplasticizer on Self-Compactability of Fresh Concrete
Authors: Ouchi Masahiro , Hibino Makoto , Okamura Hajime
Published: April 2007

The effect of superplasticizer on the balance between flowability and viscosity of mortar in self-compacting concrete was investigated quantitatively. From experimental results, the ratio of funnel speed to flow area of mortar with a fixed amount of superplasticizer was found to be almost constant, independent of the water-powder ratio. A higher amount of superplasticizer resulted in a lower ratio of funnel speed to flow area. The ratio is proposed as an index for the effect of superplasticizer on mortar flowability and viscosity from the viewpoint of achieving self-compactability. This index is convenient for evaluating the amount of superplasticizer for proper flowability and viscosity of mortar using only one set of experimental results. The relationship between superplasticizer amount and its effect was found to differ depending on the type of powder or superplasticizer. The difference can be indicated quantitatively by the proposed index.
Applicability and Significance of Rheometric Tests for Rheology of Fluid and Self-Leveling High-Strength Concrete
Authors: Nehdi Moncef , Mindess Sidney
Published: April 2007

The emergence of new special concretes on construction sites has shown that concretes of the same slump may behave quite differently on the job. For these concretes, one cannot rely on the traditional workability tests for quality control and rheological characterization. It has been claimed that the flow behavior of fresh concrete closely approximates the Bingham model and that at least two parameters are therefore needed to describe its rheology. Thus, rheological measurements must be carried out at not fewer than two shear rates. This study examines the applicability of the Bingham model to fluid and self-leveling highstrength concrete (HSC). Results obtained from a rheometer are compared with results of the standard slump test. Fluid concrete mixtures were investigated that had a water/binder ratio ( w/ b) of 0.33 and slump values of 200 ± 20 mm and incorporated proportions of limestone filler, silica fume, and ground silica as partial replacement (by volume) of cement. In addition, self-leveling concrete mixtures (torque viscosity ≤ 1 Nm at 15 min) having a w/ b ratio of 0.25 and 15 percent replacement of cement by various fillers were examined. The possibility of characterizing the rheology of fluid and self-leveling HSC on the basis of only two tests carried out at two different shear rates was addressed. An effort was made to define which is more relevant in a rheometer flow curve: the ascending part, the descending part, the maximum stress requirement, the flow resistance, the torque viscosity, or combinations of these factors. The possibility of measuring the rapid stiffening behavior of fresh HSC with time and the effect of ultrafine particles on the rheology using rheometric tests were also investigated.
Effect of Silica Fume and Superplasticizer Addition on Setting Behavior of High-Strength Mixtures
Authors: Pinto Roberto C. A. , Hover Kenneth C.
Published: April 2007

An investigation was performed to assess the influence of silica fume and superplasticizer on setting behavior of high-strength concrete mixtures. Both admixtures were added in various proportions to a mortar mixture, and setting times were determined by means of penetration resistance of freshly cast mortar. The influence of temperature was also investigated by exposing mortar specimens to different storage temperatures. Silica fume was found to shorten initial set times, whereas superplasticizer was found to delay initial set. Statistical analysis identified an interaction effect between these admixtures: the influence of one admixture on initial set depended on the amount of the other admixture. Mortar temperature not only affected initial and final set times, but also influenced the time interval between initial and final set.
Performance of Rigid Pavements Containing Recycled Concrete Aggregates
Authors: Cuttell Gregory D. , Snyder Mark B. , Vandenbossche Julie M. , Wade Monty J.
Published: April 2007

State highway agencies in Connecticut, Kansas, Minnesota, Wisconsin, and Wyoming have successfully designed and constructed rigid pavements containing recycled concrete aggregate (RCA). Success has been attributed in part to the minimization of old mortar content in the RCA during recycling processes, thereby controlling the total mortar content of the new portland cement concrete (PCC) mixture, or to the achievement of higher-than-expected compressive strengths through adjustments in mix proportions, or both. There was no clear correlation between mortar content and cracking distresses in field investigations, although one project did exhibit significantly more slab cracking in the recycled pavement than in the corresponding control pavement. The increased cracking may have been due to the large differences in total mortar content between the recycled and control sections. In general, the recycled PCC pavements considered in this study have performed comparably with their conventional PCC pavement counterparts, including the recycled pavements that incorporated RCA derived from concrete affected by D-cracking and alkali-silica reactivity (ASR). There is, however, evidence of small amounts of localized recurrent ASR in the recycled Wyoming pavement. Whether this reactivity will eventually develop into widespread distress remains to be seen.