bluuebunny/crossref_metadata_2025 huggingface dataset:
Aggregate Blending for Asphalt Mix Design: Bailey Method
Authors: Vavrik William R. , Pine William J. , Carpenter Samuel H.
Published: April 2007

From the beginning of asphalt mixture design it was desired to understand the interaction of aggregates, asphalt, and the voids created during their compaction. In asphalt mixture design, guidance is lacking in the selection of the design aggregate structure and understanding the interaction of that aggregate structure and mixture volumetric properties. Asphalt mixture design concepts are presented that use aggregate interlock and aggregate packing to develop an aggregate blend that meets volumetric criteria and provides adequate compaction characteristics. The concepts rely on coarse aggregate for the skeleton of the mixture with the proper amount of fine aggregate to provide a properly packed aggregate structure. The objective is to use aggregate packing concepts to analyze the combined gradation and relate the packing characteristics to the mixture volumetric properties and compaction characteristics. The new concepts presented for asphalt mixture design and analysis include an examination of aggregate packing and aggregate interlock, blending aggregates by volume, a new understanding of coarse and fine aggregate, and analysis of the resulting gradation. These concepts are the result of many years of field experience and are the backbone of the Bailey method for asphalt mix design. These methods are under continued development as the improved method for asphalt mixture design, which will assist with the transition to contractor mix design.
Coarse- Versus Fine-Graded Superpave Mixtures: Comparative Evaluation of Resistance to Rutting
Authors: Kandhal Prithvi S. , Cooley L.
Published: April 2007

Both coarse- and fine-graded hot-mix asphalt mixtures can be designed within the gradation control points recommended in Superpave® mix design. Some states have begun to specify only coarse-graded mixtures (below the restricted zone), whereas other states are specifying only fine-graded mixtures (above the restricted zone). A study was conducted to compare coarse-graded Superpave mixtures with fine-graded Superpave mixtures in terms of resistance to rutting to determine whether restrictions on gradations (either coarse- or fine-graded mixtures) are justified. Fourteen mixtures were tested containing two nominal maximum aggregate sizes (9.5 and 19.0 mm), two coarse aggregates (granite and crushed gravel), and four fine aggregates (sandstone, limestone, granite, and diabase). Resistance to rutting of both coarse- and fine-graded mixtures was evaluated by three test methods: asphalt pavement analyzer, Superpave shear tester, and repeated load confined creep test. Statistical analyses of the test data obtained by the three performance tests indicate no significant difference in rutting resistance of coarse- and fine-graded Super-pave mixtures. It has been recommended that mix designs not be limited to designing mixes on the coarse or fine side of the restricted zone.
Modeling City Logistics
Authors: Taniguchi Eiichi , Thompson Russell G.
Published: April 2007

Urban freight systems are experiencing many problems due to higher levels of service and lower costs being demanded by shippers, with carriers having to operate in increasingly congested road conditions. Trucks operating in urban areas produce many negative impacts for society in terms of emissions, crashes, noise, and vibration. City logistics aims to globally optimize urban freight systems by considering the costs and benefits of schemes to the public as well as the private sector. The concepts of city logistics are introduced, and an outline is presented of some models that have recently been developed to predict the consequences of intelligent transportation systems. In particular, a stochastic vehicle routing and scheduling procedure that incorporates the variation of travel times is described. Results indicate that this approach can lead to significant reduction in operating costs by carriers as well as shorter routes with fewer trucks and increased reliability for customers. This procedure also reduces emissions and fuel consumption.
Divisible-Load Permits for Overweight Trucks on Texas Highways: An Evaluation
Authors: Luskin David M. , Harrison Robert , Michael Walton C. , Zhang Zhanmin , Jamieson Jerry L.
Published: April 2007

In 1989, the Texas legislature passed HB 2060 creating an annual permit for vehicles to operate above the general weight limits. Controlled and administered by the state government, the 2060 permit has satisfied industry much more than the county-run permits it replaced. Controversial, however, has been the permit’s exemption from the special weight limits, generally 58,420 lb, that are posted on many light-duty state and county roads. County officials, in particular, have expressed concern about the damage to these roads that results from trucks traveling with up to 84,000 lb under permit. The costs of this damage are likely to far exceed the revenues from permit fees, which suggests that the permit is underpriced. Among the recommendations is the collection of additional data on the travel patterns of 2060 trucks to better determine the menu of prices and options that the permit should offer. Also recommended are returning some control over the permit system to the counties and an increased emphasis on economic efficiency in designing truck-related taxes and charges.
Sustainable Transportation U.S. Dilemmas and European Experiences
Authors: Deakin Elizabeth
Published: April 2007

The approach to sustainable transportation issues in the United States was examined in light of findings from a study of sustainable transportation planning in Sweden, Germany, the Netherlands, and Scotland. In the European countries, reducing greenhouse gases has been the initial motivation for most sustainable transportation initiatives, but broader social, economic, and environmental concerns now figure into the idea of sustainability. In the United States, barriers to greenhouse gas reduction and planning for sustainability include uncertainty about the problem and the best ways to address it, uncertainties about public support, and the lack of a clear mandate for action. Nevertheless, efforts are under way locally in the United States to promote sustainable development, and transportation plays a central role in these plans. The European organizations visited are using many of the same strategies as are U.S. planners, but supporting their efforts are strong policy commitments, government incentives, and new planning processes emphasizing collaboration and performance measurement. Tracking the comparative success of these efforts would be an important next step.
Economic Impacts of Highway Relief Routes on Small Communities: Case Studies from Texas
Authors: Handy Susan , Kubly Scott , Oden Michael
Published: April 2007

Highway relief routes, more commonly called highway bypasses, may have a variety of impacts on small communities, both positive and negative. On the positive side, communities benefit from a reduction in traffic through the heart of the community and the negative impacts that such traffic brings, including noise, emissions, and safety concerns. However, the reduction in through traffic may also have negative impacts on businesses in the community, particularly highway-oriented businesses located along the old route that are dependent on pass-by traffic. At the same time, new development may occur along the relief route corridor. How these impacts play out in a particular community depends on the characteristics of the community and the new relief route, as well as larger economic and industry trends. The research sought to identify and understand the various factors that influence the economic impacts of highway relief routes on small communities through case studies of 10 communities in Texas with relief routes and 4 without. Findings on the extent and nature of the impacts of the relief routes and the key factors determining those impacts are reported.
Assessing Noise Reflections off the Underside of Elevated Bridge Structures: Procedures Using the FHWA Traffic Noise Model
Authors: Reiter Darlene D. , Bowlby William
Published: April 2007

Noise reflections off the underside of elevated bridge structures have the potential to increase traffic noise levels and to degrade the effectiveness of noise barriers at noise-sensitive land uses near proposed highway projects. Assessing the extent to which these reflections will occur requires identifying those roadway segments from which traffic noise will reflect off the underside of an elevated bridge structure and reach a receiver. The geometry involved in assessing noise reflections can often be complex, involving numerous receivers, roadways, and barriers. Because of this complex geometry, manual analysis is beyond the scope of most noise analyses. As a result, assessing noise reflections off the underside of elevated bridge structures has traditionally been difficult and time-intensive. A procedure can be used to assess noise reflections off the underside of elevated bridge structures using features of FHWA’s Traffic Noise Model. The procedure is intended to provide a screening level of analysis to determine whether or not noise reflections off the underside of elevated bridge structures will increase traffic noise levels or degrade noise barrier performance in noise-sensitive areas. If the results of the noise reflections analysis using this screening level procedure are found to increase traffic noise levels or degrade barrier effectiveness, more detailed analysis may be warranted.
Model Predictive Control Approach for Recovery from Delays in Railway Systems
Authors: De Schutter B. , van den Boom T. , Hegyi A.
Published: April 2007

The model predictive control (MPC) framework, a very popular controller design method in the process industry, is extended to transfer coordination in railway systems. In fact, the proposed approach can also be used for other systems with both hard and soft synchronization constraints, such as logistic operations. The main aim of the control is to optimally recover from delays by breaking connections (at a cost). In general, the MPC control design problem for railway systems leads to a nonlinear, nonconvex optimization problem. Computing an optimal MPC strategy using an extended linear complementarity problem is demonstrated. Also presented is an extension with an extra degree of freedom to recover from delays by letting some trains run faster than usual (again at a cost). The resulting extended MPC railway problem can also be solved using an extended linear complementarity problem.
Chicago’s North Side ‘L’: The First Hundred Years
Authors: Allen John G. , Abrams Steven H.
Published: April 2007

Chicago’s North Side ‘L’ is the city’s most intensively used rail transit corridor. Consisting of the Red Line (Howard), Brown Line (Ravenswood), Purple Line (Evanston), and Yellow Line (Skokie Swift), this complex, interrelated operation shares a set of alignments opened for service between 1900 and 1943. After years of stable ridership, the North Side ‘L’ is now attracting increasing numbers of customers. There are plans for extending platform lengths on the Brown Line to handle passengers more effectively, and other efforts are under way that could further enhance the performance of the North Side ‘L’.
Tram-Train: New Public Transport System
Authors: Novales Margarita , Orro Alfonso , Bugarin Miguel R.
Published: April 2007

In response to the demand for improved mobility in metropolitan areas, the 1990s saw the development of a new transport system in Europe known as the tram-train. This system is based on using conventional railway lines with a low traffic density to extend urban tram (streetcar) or light rail services without changing vehicles, incorporating them into railway traffic. The tram-train enables a wider range and scope of direct transport services and reduces waiting and transfer time. The operation of light rail vehicles on conventional railway infrastructure requires the solution of numerous technical issues, such as traction power supply system, rolling stock design, gage compatibility, tire and rail profile, structural strength, passenger access, and signaling. Such problems are described and their solution by services now operating, or in advanced planning stages, worldwide is discussed.
Risk-Based Model for Identifying Highway-Rail Grade Crossing Blackspots
Authors: Saccomanno Frank F. , Fu Liping , Miranda-Moreno Luis F.
Published: April 2007

A risk-based model is presented for identifying highway-rail grade crossing blackspots. This model consists of two prediction components: collision frequency and collision consequence. A graphic approach is adopted to identify crossings with unacceptable risks (high expected frequencies or consequences or both). These crossings are referred to as blackspots. The model was applied to Canadian inventory and collision occurrence data for the period 1997-2001. Poisson and negative binomial (NB) frequency prediction expressions were developed for crossings with three types of warning devices (signs, flashing lights, and gates). The NB model was found to provide a better fit to the collision frequency data. A weighted consequence score was introduced to represent combined collision severity. The weights used in this combined consequence score were obtained from insurance claims. An NB expression was developed for the collision consequence model. The spatial distribution of blackspots is discussed with respect to the type of warning device, upgrades in warning device, geographic location, and historical collision occurrence. A geographic information system platform was developed for the Ontario region and used to illustrate the spatial pattern of expected and historical collision frequency and associated blackspots.
Long-Run Changes in Driver Behavior Due to Variable Tolls
Authors: Burris Mark W. , Konduru Karun K. , Swenson Chris R.
Published: April 2007

Managing congestion on highways, especially in urban areas, has been a major challenge for transportation planners and researchers. Variable pricing, specifically time-of-day congestion pricing, is one possible method to manage demand and reduce congestion. Because many variable pricing projects are still in the implementation stage, long-run driver responses to variable tolls are largely unknown. Long-run changes are examined in driver behavior in an existing variable pricing project in Lee County, Florida. By using empirical evidence, it was found that over time the relative price elasticity of demand on the Midpoint Memorial Bridge decreased from -0.42 to -0.11 during the early morning discount period. Elasticities have decreased, but to a lesser extent, during late morning and early afternoon discount periods. A discount period volume spreading ratio was developed, and the change in elasticity results was confirmed by using that method of analysis. It was also found that certain characteristics such as frequency of trips, commute trip purpose, full-time employment status, number of people in the household, higher education, and age between 25 and 34 years were all indicators that participants may increase their variable pricing usage over time. Other characteristics, including being retired and having a household income less than $16,000, were indicators that drivers may not increase their variable pricing participation. These results may not be typical for variable pricing facilities. Additional factors, such as the characteristics and influence of any alternate routes, traveler demographics, and size of the toll discount, need to be considered for each project. However, the methodology developed in this research can be applied to other projects to determine those price elasticities of demand and their change over time.
Results of 2003 Transportation Management Association Survey: Analysis of Evolving Characteristics of Transportation Management Associations
Authors: Hendricks Sara J.
Published: April 2007

The 2003 Transportation Management Association Survey was conducted to collect and analyze survey data to better understand national and international trends in the development and operation of transportation management associations (TMAs). TMAs provide a unique organizational structure for the delivery of mobility management services. They serve as a public-private forum for those who are directly affected to address localized transportation issues through partnership efforts. Comparisons were made with data from similar surveys conducted in 1993 and 1998. With the exception of the Netherlands, transportation management efforts in European nations are implemented through organizational structures different from TMAs as we know them in the United States and Canada. During the past 10 years TMAs have been moving toward less formalized organizational structures and fewer members but with a greater diversification in the way in which service areas are defined and in the types of members. TMAs rely less on member dues and more on federal grants. They are offering a broader range of services, reflecting efforts to tailor services to meet the needs of a greater variety of travel markets, in addition to commuters. In contrast to 1993 most TMAs now conduct employee and program evaluations. However, approximately 65% of TMAs do not have a strategic plan and 40% do not use an annual or biennial work plan. Canadian TMAs have formed to accomplish missions similar to those of their U.S. counterparts. The first Canadian TMA began in 1995, and the largest member group across all Canadian TMAs is government employers.
Alternative Methods to Increase the Effectiveness of Freeway Contraflow Evacuation
Authors: Theodoulou Gregoris , Wolshon Brian
Published: April 2007

The city of New Orleans is among the most vulnerable cities in the world to the threat of hurricanes. To protect its population from these storms, officials in Louisiana have joined a growing number of states that are planning to use contraflow freeway operations to expedite the evacuation of threatened areas. Although contraflow is widely regarded as a major advance in evacuation planning and response, no one really knows how well, or even if, it will work. Research was undertaken to improve the understanding of traffic conditions on contraflow freeway segments during an evacuation. The CORSIM microscopic traffic-simulation program was used to model the freeway configuration that will be used to evacuate New Orleans as well as two alternative scenarios for this same segment. The results showed that the currently proposed configuration might result in an underutilization of the contraflow segment, thus significantly limiting the number of evacuees who can get out of the city. The study also showed how the effectiveness of the New Orleans contraflow segment might be significantly improved with some simple and inexpensive modifications to the existing plan. Most important, the results of the research underscore the critical nature of proper planning and design of contraflow entry points and how they are often overlooked for both emergency and nonemergency conditions.
Performance Evaluation System for Main Reinforced Concrete Girders of Existing Bridges
Authors: Kawamura Kei , Frangopol Dan M. , Miyamoto Ayaho , Abe Masato
Published: April 2007

A novel performance evaluation system for main reinforced concrete girders of existing bridges evaluates durability and load-carrying capability by using technical specifications and results of simple visual inspections. Three features of the system are described. The first feature is the application of an expert system. Because the purpose of this study is to develop a novel system to evaluate the performance of a bridge element with limited information provided from simple visual inspections, it is necessary to embed into the system the knowledge of bridge experts. The second feature is a neuro-fuzzy hybrid inference. The system performs a fuzzy inference to simulate the inference mechanism used by experts for evaluating bridges. This process is integrated into a computer as a neural network; therefore, the system improves the knowledge base by using the back-propagation method. The third feature is the visualization of the inference process. The system must clearly explain how the outputs are calculated because the road networks, including bridges, represent important investments that must be carefully monitored. The learning capability of the system is demonstrated on an existing bridge in Japan. The effectiveness is verified by comparing the diagnostic results provided by a bridge expert and those proposed by the system.
Method for Priority-Ranking and Expanding Freeway Service Patrols
Authors: Khattak Asad , Rouphail Nagui , Monast Kai , Havel Jason
Published: April 2007

Freeway service patrols (FSPs), classified as part of intelligent transportation systems, are programs that use roving vehicles to patrol congested and high-incident sections of freeways; they help to smooth traffic flow by aiding stranded motorists and assisting in incident clearance. Many major urban areas currently have patrols, and most medium-sized urban areas are following suit. The success of FSPs has resulted in frequent requests for service expansion. However, the decision on where to put the next patrol is becoming more difficult because an assessment of greatest need typically indicates that high-priority areas already have the service, whereas the possible effects of the service are often indistinguishable on lower-priority facilities. A new approach was developed to help determine the most beneficial locations for patrol deployment by using expanded placement criteria. North Carolina was used as a case study. Analysis of three incident and crash indexes was combined with spatial analysis, incident type distributions, average hourly freeway traffic volumes, and incident delay estimations to identify, evaluate, and compare candidate facilities for FSP expansion. Results of the research were incorporated into a decision support tool that allows easy planning and operational assessment of candidate sites by comparing performance values between sites, modeling the effect of FSPs, and estimating their key potential benefits. By using the tool, decision makers can quickly assess the needs of different facilities and make an informed, cost-effective decision on where to implement the next service patrol.
Minnesota's New Ramp Control Strategy: Design Overview and Preliminary Assessment
Authors: Xin Wuping , Michalopoulos Panos G. , Hourdakis John , Lau Doug
Published: April 2007

Freeway ramp control has been successfully implemented in the Minneapolis-St. Paul area since the early 1970s. However, the recent ramp metering controversy highlighted the need for a less restrictive ramp control strategy that maximizes freeway capacity utilization while limiting ramp wait times. As a result, a new multilayer ramp control strategy called stratified ramp control was recently developed and deployed systemwide in the Twin Cities metropolitan area. This strategy determines the metering rates from freeway conditions as well as from real-time ramp demand and ramp queue size, indicating a shift of emphasis away from freeway flow toward the balance between both freeway efficiency and reduced ramp delays. Minnesota's new ramp control strategy is detailed along with a preliminary assessment of its effectiveness. The evaluation is accomplished by comparing the new strategy to its predecessor, ZONE metering, through rigorous micro-simulation. The preliminary results suggest that the stratified ramp control strategy is effective in reducing ramp delays and limiting ramp wait times below the prescribed value. However, peak-hour freeway congestion is extended in both time and space as opposed to that with the ZONE metering strategy and reveals a compromised freeway performance in favor of virtually reducing ramp delays.
Single-Intersection Evaluation of Real-Time Adaptive Traffic Signal Control Algorithms
Authors: Shelby Steven G.
Published: April 2007

Adaptive traffic signal control systems present the potential to significantly reduce delay, travel time, stops, and fuel consumption relative to current arterial traffic management practices. However, this technology—now referred to as adaptive-control software (ACS) by FHWA—has not been widely deployed in the United States, in part because traffic engineers are unconvinced of the incremental benefits of ACS over those of well-maintained time-of-day plans. This study identifies three specific deficiencies in the current generation of adaptive-control algorithms. Primarily, the inability to optimize timing in general multiring configurations prevents current adaptive-control algorithms from consistently out-performing properly calibrated dual-ring vehicle-actuated controllers. Limitations in real-time computational capabilities are identified as the main roadblock to overcoming this and other deficiencies. This limitation motivates a novel simulation study focused on real-time computational capabilities of adaptive-control algorithms used in OPAC, PRODYN, ALLONS-D, and COP, the intersection control algorithm of RHODES. The goal is to determine which algorithmic techniques are best suited for extension or reformulation to overcome the identified deficiencies. Benchmarks for vehicle delay performance include Webster's optimized fixed-time control, vehicle-actuated control, and an adaptive fixed-time policy derived from SCOOT. In conclusion, certain aspects of algorithmic techniques from OPAC, PRODYN, and ALLONS-D are unsuitable for much more computationally demanding tasks, including future extension to full optimization of a multiring controller. Also, specific features of the COP-97 and ALLONS-D algorithms present significant advantages in computational complexity and reduced traffic delay, respectively.
Online Travel Time Estimation Without Vehicle Identification
Authors: Lucas David E. , Mirchandani Pitu B. , Verma Nitasha
Published: April 2007

A new approach is presented to the estimation of travel times (in real time) on arterials on the basis of second-by-second data from detectors that count vehicles. Unlike most approaches, which attempt to track individual vehicles as they move throughout the network, the proposed approach tracks clusters, or platoons, of vehicles. This approach offers several advantages over existing methods and provides good travel time estimates for arterial networks. Although other methods of estimating travel times have varying degrees of success, they each suffer from limitations ranging from processing, equipment, and infrastructure requirements to personnel cost for probe vehicles, sociopolitical issues of surveillance, and the perceived loss of privacy. The proposed method attempts to overcome some of these limitations. Because existing detection and controller infrastructure is used, additional equipment is not required. Second-by-second detector data are used to identify platoons of vehicles but not individual vehicles. The platoons, and not individual vehicles, are then tracked as they travel from upstream detectors to downstream detectors on a route segment, producing travel time estimates for this segment. In addition, since the proposed method captures the aggregate flow of vehicles, it should better measure the central tendencies of the driver population and current traffic conditions as reflected by travel times at the prevailing congestion levels.
Benefit Assessment of Implementing Weather-Specific Signal Timing Plans by Using CORSIM
Authors: Lieu Henry C. , Lin Shiow-Min
Published: April 2007

The effect of weather on the nation's surface transportation systems touches people every day. Each year 7,000 fatalities and 800,000 injuries involve weather-related adverse road conditions as a factor. These statistics represent about 28% of all highway crashes and 19% of all fatalities. The estimated annual economic cost due to weather-related crashes (deaths, injuries, and property) amounts to nearly $42 billion. Adverse weather has a significant impact on traffic operations and is a challenging issue to traffic engineers. However, there is a perception that traffic engineers can do little to mitigate the effects of weather, which is the result of two main factors: ( a) no specific tools are currently available for traffic engineers to assess weather impacts on traffic operations and ( b) both traffic and weather data are lacking for traffic analyses. As a result, traffic engineers have little understanding of traffic behaviors due to loss of visibility and traction in bad weather. As more road weather information systems and intelligent transportation systems are deployed and integrated, a large amount of traffic and weather data will become available. Data availability and powerful traffic simulation tools make it possible for engineers to develop and assess weather-specific traffic operations strategies to mitigate congestion in bad weather. The purpose of this study is to use CORSIM (a microscopic traffic simulation model) to illustrate a procedure for assessing benefits of retiming traffic signals in bad weather for both principal arterials and regional networks. Some preliminary findings and gaps identified for further research are also provided.
Development of a Java Applet for Generating Truck Trips from Freight Data
Authors: Klodzinski Jack , Ahmad Al-Daraiseh , Georgiopoulos Michael , Al-Deek Haitham M.
Published: April 2007

As freight transportation becomes a more significant concern, the ability to estimate accurately truck trips generated by freight activity at an intermodal facility is important for transportation engineering and planning. Truck trip generation models that used vessel freight data were developed by the University of Central Florida Transportation Systems Institute and have been statistically proved to determine accurately the number of trucks generated at a seaport. To apply these previously developed models more efficiently, a Java applet was developed to execute a selected artificial neural network (ANN) port model and a trainable ANN port model. This applet provides the user with an easy-to-understand interface for entering data and executing models. The two models developed were the Port Everglades ANN model and a hybrid of the Port Everglades model that allowed the user to retrain the ANN model before execution for desired data. Although the trainable model requires additional retraining with new data, the added complexity comes with the benefit of producing a network with a higher degree of accuracy. This applet equips the user with two models and therefore has expanded the capabilities of the previously limited Port Everglades ANN truck trip generation model. The developed Java applet can be expanded to include more ANN models and thus more flexibility, depending on the type of freight data available. This successful adaptation of the ANN model into a Java applet sets the foundation for further applications.
Investigation of Dynamic Probe Sample Requirements for Traffic Condition Monitoring
Authors: Green Matthew W. , Fontaine Michael D. , Smith Brian L.
Published: April 2007

Many agencies are exploring the use of probe-based traffic monitoring systems to collect information on system performance. Although these systems offer the potential of directly measuring travel times and of significantly reducing the cost per mile of traffic monitoring systems, the issue of identifying the number of samples required to produce reliable and accurate condition information has not been adequately examined. Most existing research into this issue addresses the problem from a very broad perspective, offering a single percentage of vehicles in an area that must be equipped as probes to provide good coverage of the area. This approach ignores variations in flow conditions through time and across different links of the network. The described research addresses the issue of sample sizes for different links and measurement intervals from a rigorous statistical perspective. First, the issue of producing sample sizes on the basis of the central limit theorem (CLT) is empirically examined by using Virginia freeway speed data to assess this method's validity even when the underlying speed population is nonnormal. Applying the CLT to the speed data shows that fluctuations in flow conditions over time and across different locations require varying sample sizes, which the static sample sizes proposed in previous research do not take into account. Finally, the CLT-based sample sizes are compared with a representative static sample size proposed in the literature to illustrate how the CLT method can reduce sample sizes while maintaining the desired confidence and accuracy levels.
Defining and Measuring Traffic Data Quality: White Paper on Recommended Approaches
Authors: Turner Shawn
Published: April 2007

Recent research and analyses have identified several issues about the quality of traffic data available from intelligent transportation systems for transportation operations, planning, or other functions. FHWA contracted with Battelle, the Texas Transportation Institute, and Cambridge Systematics to develop an action plan to help stakeholders address traffic data quality issues. The project team developed a series of three white papers that addressed traffic data quality issues, and regional stakeholder workshops were held in Columbus, Ohio, and Salt Lake City, Utah, to critique the white papers and gather input for the traffic data quality action plan. Recommendations are provided for defining and measuring traffic data quality. Data quality is defined as "the fitness of data for all purposes that require it. Measuring data quality requires an understanding of all intended purposes for that data." Six key data quality measures are recommended: accuracy, completeness, validity, timeliness, coverage, and accessibility. Although examples and definitions of these data quality measures are given, future work will more clearly define the calculation and use of these data quality measures in different application areas of transportation.
Estimating Eligibility Rates: Crucial Component of the Calculation for Response Rates
Authors: Alsnih Rahaf , Stopher Peter R.
Published: April 2007

Response rates are used by analysts to assess survey quality: higher response rates usually are desired to reduce the incidence of nonresponse bias. The response rate is defined as the ratio of the number of completed interviews divided by the number of eligible sample units. However, because of the inconsistency of the definition of response rates often quoted in travel surveys, it is difficult to state explicitly that declining response rates are the result of fewer people willing to participate in surveys or are attributed to the calculation of response rates. Most likely it is a combination of these two factors. Two well-known formulas used to calculate response rates are described: the Council of American Survey Research Organizations formula and the American Association for Public Opinion Research formula. The difference between these formulas lies in the estimate of eligible sample units among the sample units of unknown eligibility. Through examination of two call history files, the recruitment phase for two household travel surveys, eligibility rate estimates for the sample units of unknown eligibility were calculated and used in the response rate formulas. The rates of eligibility for the sample units of unknown eligibility were higher than the eligibility rates for the units of known eligibility. These results were not expected and further confirm that agencies must treat units of unknown eligibility carefully when calculating response rates.
Estimating Spatial Measures of Roadway Network Usage from Remotely Sensed Data
Authors: Coifman Benjamin , Yang Yongliang
Published: April 2007

Roadway network usage is measured for purposes as diverse as design, planning, maintenance, operation, management, and research. Traditionally, these measurements are made with ground-based sensors. The sensors provide a temporally rich data set, but an individual sensor's lack of spatial coverage limits use and application. High-resolution imagery remotely sensed from satellite or airborne platforms is an attractive alternative that can potentially supplement and enhance the existing traffic monitoring programs with a spatially rich data set. Spatial measurements of network usage as extracted from remotely sensed data are demonstrated.
Loop Detector Data Diagnostics Based on Conservation-of-Vehicles Principle
Authors: Vanajakshi Lelitha , Rilett L. R.
Published: April 2007

Inductive loop detectors are the most popular method for continuously collecting traffic data over an extended period and over large spatial areas. These data are used in several applications, including real-time traffic information graphical displays, traffic forecasting programs, and incident management systems. The accuracy and reliability of the data generated by the loop detectors ultimately determine the quality of the results of the end application. However, the main criticism of detector data is the high probability of error because of equipment malfunctions. Traditionally, gross errors are identified by using threshold checking on speed, volume, or occupancy observations, either individually or in combination at individual locations. A more robust approach would include a check for conservation of vehicles over a series of detectors. However, this approach has received little attention. A constrained nonlinear optimization approach is presented for identifying and correcting loop detector data obtained from the field, in situations in which the data violate the vehicle conservation principle. The generalized reduced gradient method is adopted, and the objective function and constraints are selected so that the result will follow the conservation principle with the least change of the original data. This proposed technique can also be used to impute missing data and to locate suspect detector stations among a series of detector locations. Loop detector data from San Antonio are used as a test bed.
Waterways and Livelihoods: Journey to the Mainstream?
Authors: Czuczman Kate
Published: April 2007

For many of the poorest people in the world, water transport is the only means of mobility and access to basic services. Improvements in rural water transport (RWT) technologies, infrastructure, and services can help eliminate poverty and reduce isolation. Yet in a transport climate dominated by motorized vehicles and roads, traditional waterways have been neglected and deprioritized. The importance of RWT in the lives of the rural poor is explored by examining the results of the International Forum for Rural Transport and Development's Waterways and Livelihoods networked research project. Why RWT has become a marginalized issue is discussed. A new networking and information resource that promotes the integration of RWT through improved policy and practice both within the transport sector and in the wider development community is introduced. The lack of integration of RWT in mainstream transport and development planning is manifest in the deterioration of traditional waterways and infrastructure and in conflicts between waterway use and land transport (or other) interventions. The consequences of this lack of integration are lost opportunities for poor people to improve their livelihoods and lost potential to develop ecologically and financially sustainable transport technologies. Why has RWT been neglected? The Waterways and Livelihoods research identified a lack of positive visibility as the prevailing factor, including poor perceptions of RWT as outmoded and unsafe, a dearth of reliable statistical information on the sector, and an "unfair playing field" on which RWT suffers in comparison with other transport options.
Willingness to Pay for Water Transportation in the Ohio River Basin
Authors: Bray Larry G. , Dager Chrisman , Burton Mark L.
Published: April 2007

The question of elasticity was raised to a high level in the Upper Mississippi-Illinois Waterway River Navigation study undertaken by the Rock Island District of the U.S. Army Corps of Engineers in 1994. That study, in contrast to earlier works, assumed that every shipment was sensitive to price. National Academy of Sciences reviewers supported the idea of using barge demand functions that were responsive to price but were critical of assuming this distribution rather than measuring it empirically. A study to provide information on shipper willingness to pay for barge transportation was conducted. Interviews of barge transportation providers and users regarding shipper willingness to pay are summarized, and factors affecting demand are discussed. An early attempt to estimate barge price elasticities and the problems inherent in this type of analysis are also discussed. Significant interview findings were that shippers on the Ohio River Basin navigable streams made a decision to locate there and that they would pay much more than the next least costly rate to maintain barge transportation. The findings also indicated that if commodities had a high value, were not dangerous to the public, and moved in fairly small quantities, shippers would shift from barge to rail for a small rate savings. Traditional short-run demand relationships were difficult to estimate with cross-sectional data maintained by the Tennessee Valley Authority. It appears that in many settings output decisions and decisions regarding distribution channels are made in advance of transportation considerations, so that output quantities and shipment destinations are parametric in a transportation cost minimization process.
Inland Sulfate Deposition in North America from Marine Emissions
Authors: Gurian Patrick L. , Corbett James J.
Published: April 2007

Sulfate emissions from marine transport are an important part of the global sulfate emissions inventory. This study estimates long-term average sulfate deposition from marine transport in two general areas of the United States: the West Coast and the Great Lakes region. An analytical model of sulfate dispersion and reaction is used to predict combined wet and dry deposition rates. Emissions are roughly three times higher in the Great Lakes region than off the West Coast and result in substantially higher deposition rates from marine transport. In all locations studied, the contributions of marine transport to overall deposition rates were modest, in the range of 0.2 kg/ha-year to 2 kg/ha-year. Under-standing the contribution from marine sources will help improve overall estimates of the sources of acid deposition and help focus regulatory attention on the most promising areas for reducing deposition rates in inland areas.
Can Chemical Modification of Paving Asphalts Be Equated to Polymer Modification?: A Laboratory Study
Authors: Ajideh Hossein , Rangel Andres , Bahia Hussain
Published: April 2007

Chemical modification of asphalt by acid has been known for quite some time. Chemically modified asphalts can extend the upper application temperature limit and prevent rutting of asphalt mixture by increasing asphalt stiffness. During the past two decades, many studies focused on polymer modification have indicated that polymer additives can successfully improve asphalt pavement performance. The low cost of acid modification, relative to polymer and other modifiers, makes the acid modification alternative important and competitive. Unlike the situation with other modifiers, information about chemically modified asphalts is limited, and performance data are almost nonexistent. During the past few years, major advancement in characterization of load-related damage resistance behavior of asphalts has been achieved. A new protocol for measuring resistance of binders to rutting and fatigue has been introduced by the NCHRP 9-10 project. In addition, new protocols to measure construction-related properties, such as zero shear viscosity for mixing and compaction temperatures and storage stability, are proposed. The effectiveness of chemical treatments with acid and polymer modifier in improving performance-related properties of paving asphalt were evaluated. The results indicated that chemically modified asphalts show significant improvement in rutting and fatigue resistance. However, the effect of aging on rheological properties of chemically modified asphalts was significantly different from its effect on polymer-modified asphalt. There are also indications that resistance to moisture damage of mixtures produced with the chemically modified asphalts is not as good as that for mixtures made with polymer-modified asphalts.
Role of Modified Binders in Rheology and Damage Resistance Behavior of Asphalt Mixtures
Authors: Soleymani Hamid R. , Zhai Huachnun , Bahia Hussain
Published: April 2007

Rheological and damage characterization of asphalt mixtures under dynamic loading and different frequencies and temperatures can simulate a wide range of traffic loads and climate conditions. Unfortunately, the characterization of asphalt mixtures by their rheological properties requires considerable time, financial resources, and equipment—elements that are not readily available to contractors and design engineers in most firms. Consequently, researchers have made significant attempts to estimate the dynamic properties of asphalt mixtures on the basis of their binder and aggregate properties. This study attempts to add to existing knowledge in the area of modified asphalt mixture by presenting data from 36 different mixtures produced from 9 different modified binders, all tested for their rheology, rutting, and fatigue resistance. A set of simple models is offered to quantify the relationship between binder properties and mixture properties including the complex shear modulus G*, rutting, and fatigue life. G* of modified mixtures could be represented by a simple power law function of G* of modified binders. The change in the binder rutting rate of mixtures is approximately 20% that of binders. Also shown is that changing the fatigue life of binders by 100% can result in a 20% change in the fatigue life of mixtures. Although the relationships are not fundamental and are entirely phenomenological, they provide good first approximation tools to quantify the effects of binders and thereby inform initial decisions regarding the importance of modified binders in pavement performance.
Assessing Uncertainties in Traffic Simulation: A Key Component in Model Calibration and Validation
Authors: Bayarri M. J. , Berger James O. , Molina German , Rouphail Nagui M. , Sacks Jerome
Published: April 2007

Calibrating and validating a traffic simulation model for use on a transportation network depend on field data that are often limited but essential for determining inputs to the model and for assessing its reliability. Quantification and systemization of the calibration/validation process expose statistical issues inherent in the use of such data. These issues are discussed, and a methodology to address them is described. The formalization of the calibration/validation process leads naturally to the use of Bayesian methodology for assessing uncertainties in model predictions arising from a multiplicity of sources (randomness in the simulator, statistical variability in estimating and calibrating input parameters, inaccurate data, and model discrepancy). The methods and the approach are exhibited on an urban street network with the microsimulator CORSIM, and the demand and turning movement parameters are calibrated. A discussion of how the process can be extended to deal with other model parameters as well as with the possible misspecification of the model is included. Although the methods are described in a specific context, they can be used generally, although they are inhibited at times by computational burdens that must be overcome, often by developing approximations to the simulator.