bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal Imaging of Hot-Mix Paving Operations for Quality Assessment
Authors: Sebesta Stephen , Scullion Tom , Liu Wenting , Harrison Gerry
Published: May 2018

In the mid-1990s, thermal imaging was identified as a technology that might locate segregation in hot-mix paving operations. In 2000, work started in Texas to evaluate the utility of infrared imaging for identifying segregation. Work conducted in Texas verified that temperature differentials did relate to changes in important hot-mix asphalt properties. This early work also showed that temperature differentials greater than 25°F (13.9°C) typically indicated problems in Texas mixes. With confidence in the utility of the technology, and recommended limits for temperature uniformity, Texas recently made substantial progress tailoring thermal data collection technology and data processing capabilities to hot-mix paving operations. The development and application of the current state of the practice for evaluating paving operations with thermal imaging in Texas are presented. The current methodology in Texas uses the Pave-IR system, which consists of a transverse bar with 10 infrared sensors immediately behind the paver, and the Pave-IR software package, which collects and displays the thermal profile in real time as the paving train progresses. In addition to real-time data display, Pave-IR can display in real time whether the paving temperatures fall within user-defined limits and, during paving Pave-IR, can provide a histogram of temperatures every 100 ft (30.5 m). Postprocessing functions in Pave-IR consist of data playback and review, spot temperature display, and creation of a histogram of the placement temperatures for the entire data file.
Evaluation of Superpave Mix Design for Low-Volume Roads in New Jersey
Authors: Vitillo Nicholas P. , Bennert Thomas , Smith Joseph , Maher Ali
Published: May 2018

This research project explored the implementation of the Superpave® mixture design system for use on low-volume roads in New Jersey by comparing them with well-performing Marshall mixtures. The research used a reverse-engineering approach to examine mixture blend gradations, volumetric properties, performance, and durability of well-performing Marshall mixtures compared with Superpave mixtures for low-traffic-level applications. In addition, the research evaluated the number of gyrations needed to produce equivalent air voids to the well-performing Marshall mixtures in the Superpave gyratory compactor. The gradations of the fine-graded Marshall mixtures from four suppliers were used to develop corresponding Superpave mixtures in the lab. The comparison of the Superpave and Marshall mixtures showed that they had similar volumetric, rutting, fatigue, permeability, and average asphalt binder thickness characteristics. The research also established relationships between Gsb or Gmm and the number of gyrations needed to reach air void levels similar to the Marshall mixtures.
Sensitivity Analysis of 2002 Design Guide Distress Prediction Models for Jointed Plain Concrete Pavement
Authors: Kannekanti Venkata , Harvey John
Published: May 2018

The AASHTO 2002 design guide was calibrated with Long-Term Pavement Performance sections scattered throughout the United States but with very few sections from the state of California. To understand the reasonableness of the model predictions for California conditions, a detailed sensitivity study was undertaken. The reasonableness of the model predictions was checked with a full factorial considering traffic volume, axle load distribution, climate zones, thickness, design features, portland cement concrete (PCC) strength, and unbound layers. Satellite sensitivity studies were performed to study the effects of surface absorptivity and coefficient of thermal expansion, which were not included in the primary sensitivity analysis. The findings are summarized from about 10,000 cases run with the software as part of this study. The cracking model was found to be sensitive to the coefficient of thermal expansion, surface absorptivity, joint spacing, shoulder type, PCC thickness, climate zone, and traffic volume. The faulting values are sensitive to dowels, shoulder type, climate zone, PCC thickness, and traffic volume. Although on average both the cracking and faulting models show trends that agree with prevailing knowledge in pavement engineering and California experience, in some cases results were counterintuitive. These cases include thinner sections performing better than thicker sections and asphalt shoulders performing better than tied and widened lanes. It was also found that the models fail to capture the effect of soil type and erodibility index and that the cracking model is sensitive to surface absorption.
Effect of Load Spectra on Mechanistic–Empirical Flexible Pavement Design
Authors: Timm David H. , Bower Julia M. , Turochy Rod E.
Published: May 2018

The transition from equivalent single-axle loads to load spectra represents a significant change in traffic characterization as many agencies begin the migration from empirically based pavement design methods to mechanistic–empirical (M-E) approaches. A key issue lies in determining appropriate representative load spectra that can be used for design. Previous studies have examined differences between load spectra and have largely found them statistically different and site-specific. This study proposes an approach to evaluating different load spectra in terms of practical effects on resulting flexible pavement thickness design. Load spectra from 12 sites in Alabama were evaluated against a statewide load distribution. Customized M-E design software featuring Monte Carlo simulation and layered elastic analysis generated pavement response distributions for a range of three-layer pavement structures. The responses were transformed through calibrated transfer functions into predictions of pavement performance from which required thicknesses were derived. For the 36 design scenarios considered (3 soil types and 12 load spectra), approximately 86% of the design thicknesses were within 0.5 in. of the thickness determined from the statewide load spectra. It was concluded that, in practical terms, statewide load spectra are warranted for use and will not adversely affect most pavement designs. However, local knowledge and experience should be used to determine when site-specific data should be collected for pavement design.
Effects of Outsourcing and Performance-Based Contracting on Innovations
Authors: Stenbeck Torbjörn
Published: May 2018

A savings of 13% to 28% was recorded as outsourcing and performance-based contracting were introduced in Swedish highway maintenance, in line with 21% gained in Massachusetts and 12% in Virginia. Few negative effects on service, environment, and quality were noted. However, there is concern that a slowdown of research and development (R&D) and innovations may lead to higher costs and a less effective transport system in the long run. France has used a benchmark for the effects on technical development, with an in-house policy similar to Sweden's before the reform. Initial results of an explorative study are that France has continued to produce technical development in the same period while it seems to have stalled in Sweden. This international comparison tends to support that outsourcing has lowered the pace of R&D compared with a situation if the in-house production system prevailed. However, innovation frequency is not a goal itself, so further study is needed to find the optimal mix of measures to develop an effective transport system. Professionals and politicians representing the Swedish taxpayers are reluctant to return to in-house production just to produce perhaps unnecessary technical development. Instead, the policy to develop complementary innovation promotion within the outsourcing model will continue. Measures within or complementary to the model are multicriteria bid evaluation, alternative bids, on-line monitoring, bonus, penalties and profit sharing, competence development, partnering, and weather-regulated performance- based contracting. Such measures are used and evaluated continuously.
Estimating Interstate Highway Capacity for Short-Term Work Zone Lane Closures
Authors: Sarasua Wayne A. , Davis William J. , Chowdhury Mashrur A. , Ogle Jennifer H.
Published: May 2018

Defining and understanding traffic flow parameters within short-term Interstate work zones are crucial in developing effective policies to manage construction and maintenance work conducted on the nation's heavily traveled freeways. The South Carolina Department of Transportation (DOT) initiated a research study to develop a methodology for use in determining an updated lane closure policy for Interstate highway work zones. Phase 1 of the research was completed in May 2003, and findings identified threshold volumes for two-to-one lane closure work zone configurations. Phase 2 of the research further expanded numerically derived relationships and contained analysis of other short-term lane closure configurations including three-to-two and three-to-one lane closures. Both research phases concentrated on methods to determine the number of vehicles per lane per hour that can pass through short-term Interstate work zone lane closures with minimum or acceptable levels of delay as defined by South Carolina DOT. Phase 2 includes an expanded list of data collection sites with differing work zone characteristics. This paper presents the analysis and results of Phase 2 of the research. Headway analysis revealed that passenger car equivalents (PCEs) differed for various speed ranges and modified PCEs for various speed groups were applied in calculating capacity. A model for calculating work zone capacity that incorporates base capacity, PCEs for various speed groups, adjustment factors related to specific work zone characteristics, and number of lanes open through the work zone, is recommended.
Internal Traffic Control Plans and Worker Safety Planning Tool
Authors: Graham Jerry L. , Burch Robert
Published: May 2018

The safety of pedestrian workers and construction vehicle operators can be enhanced by a carefully prepared internal traffic control plan (ITCP) administered by a competent person. Time and effort spent in preparing and using an ITCP should lower the rate of occupational injuries and fatalities experienced by construction personnel. This paper describes the purpose and components of ITCPs and presents details of a number of highway worker accidents and discusses how an ITCP prepared by a competent person on the project could have prevented or lessened the severity of the accident. Results of observation of paving at four sites in Arizona and recommendations for preparation and use of ITCPs are also discussed. Accident details are taken from several investigations and from Fatality Assessment and Control Evaluations funded by the National Institute for Occupational Safety and Health. During the study of four paving sites, a guide for preparing and administering ITCP was prepared.
Pavement Friction in a Program to Reduce Wet Weather Traffic Accidents at the Network Level
Authors: Murad Maher M. , Abaza Khaled A.
Published: May 2018

Approximately 20% of all traffic accidents occur in wet weather conditions. Pavement surface problems, such as lack of skid resistance, probably contributed to a portion of those vehicle accidents on wet pavements. An approach for reducing wet weather accidents was developed. The main feature of the proposed approach is that it uses data from both automated accident and skid data files. The contents of both skid number (SN) and accident files were studied. The related parameters in the skid file were selected, including the skid number, and a group of accident parameters was defined. The skid and accident files were merged to allow for developing a program that identifies “high-risk” locations for treatment. Such locations are expected not only to have high wet weather accidents but also to have experienced a critical number of wet weather accidents. An example is used to illustrate the functionality and effectiveness of the proposed approach and the associated computer program. Accident history was obtained on approximately 500 rural two-lane highway sections over a 3-year period. The total traffic accidents involved was approximately 36,000. A criterion to estimate possible risks was developed, and a system of priority ratings, based on economic analysis, was established to assist in the process of selecting slippery highway sections for maintenance, permitting available funds to be allocated optimally.
Effect of Truck Suspension and Tire Properties on Pavement Damage Spatial Distribution
Authors: Romero José Antonio , Lozano Alejandro
Published: May 2018

Strain energy is stored within pavement by a measured distribution of heavy vehicle traffic. A simulation methodology based on this strain energy is proposed to study the spatial distribution of pavement damage. Stored energy in the model depends on the magnitude and speed of the tire loads and on the pavement response. Pavement response is a function of different asphalt binder and mix properties, including temperature, softening temperature, void content, and penetration index. Aggregated stored energy for measured heavy vehicle traffic is obtained in terms of suspension stiffness and damping and tire stiffness properties. A pavement–traffic model is derived after linear in-plane vehicle models are integrated with the distributed pavement model. The accumulated stored energy is compared with AASHO test data to validate the proposed methodology. Results for the spatial concentration of the potential road damage revealed that normalized-to-average difference between the maximum and minimum values for pavement potential damage along the road profile is a function of pavement roughness, with average values of approximately 45%, 20%, and 11.5% for rough, medium-rough, and smooth pavements, respectively. Variations in normalized road damage concentration because of changing suspension and tire properties are from 40% to 50% for a rough pavement, from 18% to 22% for a medium-rough pavement, and from 9% to 14% for a smooth pavement.
Describing the Evolution in the Number of Highway Deaths by Decomposition in Exposure, Accident Risk, and Fatality Risk
Authors: Hermans Elke , Wets Geert , Van den Bossche Filip
Published: May 2018

The general purpose of this research is to improve insight into road safety on Belgian highways by means of a layered model. The monthly number of persons killed on highways in Belgium is decomposed into three parts: exposure, accident risk, and fatality risk. The evolution in each of these dimensions is investigated separately. More specifically, for each dimension a descriptive and explanatory analysis reveals the optimal unobserved components model. The separate analysis of each dimension may reveal different underlying developments. The impact of meteorological, socioeconomic, legislative, and calendar factors on exposure, accident risk, and fatality risk is investigated. The analysis indicates that, although for each dimension the same basic components are available, the optimal model of each dimension has its unique structure of descriptive components and significant variables. Precipitation and snow enhance accident risk, while temperature plays a significant role for exposure. Fatality risk decreases in case of an extra day with precipitation and was significantly affected by the child restraint law. The economic indicators mainly affect accident risk. When the three models are brought back together, the number of highway deaths between 1993 and 2001 is well reconstructed.
Effects of Sample Size on Goodness-of-Fit Statistic and Confidence Intervals of Crash Prediction Models Subjected to Low Sample Mean Values
Authors: Agrawal Ravi , Lord Dominique
Published: May 2018

The statistical relationship between motor vehicle crashes and covariates can generally be modeled via generalized linear models (GLMs) with logarithmic links with errors distributed in a Poisson or Poisson-gamma manner. The scaled deviance and Pearson's χ2 have been proposed to test the statistical fit of GLMs. Recent studies have shown that these two estimators are not adequate for testing the goodness of fit (GOF) of GLMs when they are developed from data characterized by low sample mean values. To circumvent this problem, a testing method has been proposed to evaluate the GOF of such GLMs. Because this method can be time-consuming to implement, there is a need to determine whether it is sensitive to different sample sizes. The primary objective of this paper is to investigate the effects of decreasing sample sizes on the GOF testing technique. A secondary objective is to estimate how the reducing of sample size influences the confidence intervals of GLMs. To accomplish the objectives, GLMs were fit with the use of two data sets subjected to average and low sample means collected in Toronto, Ontario, Canada. Several models were estimated for different sample sizes. The results of the study show that the testing technique is more effective for smaller than for larger samples when data are subjected to low sample mean values. The results also show that the width of the confidence intervals increases, as expected, as the sample size decreases and can be extremely large for small sample sizes. Hence, statistical models characterized by low sample mean values should be developed on the basis of a large number of observations. Data sets containing at least 100 observations (e.g., intersections, segments) are recommended in the development of models. The paper concludes with recommendations for future studies involving such data sets.
Using the Rural Two-Lane Highway Draft Prototype Chapter
Authors: Fitzpatrick Kay , Schneider William , Carvell Jim
Published: May 2018

The TRB Highway Safety Manual Task Force is providing direction and oversight in the preparation of a new document to be called the Highway Safety Manual (HSM). The complete version of the HSM is expected to be released to the public in 2007. A draft prototype chapter (DPC) for rural two-lane highways is available for review. A Texas Department of Transportation project explored the use of the DPC by applying the methodology to two case studies and exploring methods to develop calibration factors. The lessons learned from the effort can be used to improve the DPC along with other chapters in development. Additional guidance is needed on ( a) how to identify segments, ( b) acceptable minimum segment lengths, ( c) how best to combine the predictions for intersections with those for tangents and curves, ( d) the key variables within the procedures and appropriate assumptions when data for those variables are not available, ( e) the confidence in the approach for individual roadway segments as opposed to a roadway, ( f) the potential of using confidence intervals in the prediction process, and ( g) how best to use the predictions generated from the methodology.
Application of Highway Safety Manual Draft Chapter
Authors: Sun Xiaoduan , Li Yuebin , Magri Dan , Shirazi Hadi H.
Published: May 2018

Predicting highway safety performance in quantitative terms on the basis of a set of highway geometric design and traffic control features is the core of the ongoing Highway Safety Manual (HSM) development. While great efforts have been made to develop safety performance models for different types of highways, evaluating the applicability of the models with crash data from states that were not used in the original model development is equally important. This step is critical in future HSM applications because of many noticeable differences in crash data recording practice and driving behaviors across the various states. Potential application concerns need to be evaluated fully and addressed before the manual is officially published. This paper presents the application experience of the safety prediction models and methodology for segments of two-lane rural roads as proposed for inclusion in Part III of the HSM. The study used data for state routes in Louisiana. The results indicate that the prediction models performed reasonably well: there were small differences between the observed and predicted crash frequencies, with calibration parameters applied, for all segments on rural two-lane highways in Louisiana. The results at different analysis levels (from individual segments to a network of segments) are summarized, and several application issues such as the level of effort versus degree of accuracy, simplification of the calibration process, and the need for a reliability measurement are discussed.
Modeling Passengers’ Preferences on a Short-Haul Domestic Airline with Rank-Ordered Data
Authors: Bekhor Shlomo , Freund-Feinstein Uzi
Published: May 2018

In recent years, interest in finding methods to measure and analyze airline passengers’ preferences has been growing. The current state of the air transportation industry encourages the implementation of tools and methodologies for such purposes. Initial modeling results of research on the preferences of domestic airline users are presented. A field survey (computerized questionnaire on a laptop computer) was conducted in five of Israel's domestic airports. Respondents were asked to rank four alternatives as main level-of-service variables. Separate models were estimated for three passenger trip purposes: personal, tourism, and business. The results of single-choice and rank-ordered logit models are compared for all available observations. The results indicate that the combination of first- and second-rank data sets produces coefficient estimates that are efficient but not significantly better than those of the single-choice logit models.
Risk Aversion to Short Connections in Airline Itinerary Choice
Authors: Theis Georg , Adler Thomas , Clarke John-Paul , Ben-Akiva Moshe
Published: May 2018

Network airlines traditionally attempt to minimize passenger connecting times at hub airports, assuming that passengers prefer minimum scheduled elapsed times for their trips. However, minimizing connecting times creates schedule peaks at hub airports. These peaks are extremely cost-intensive in terms of additional personnel, resources, runway capacity, and schedule recovery. Consequently, passenger connecting times should be minimized only if the anticipated revenue gain of minimizing passenger connecting times is larger than the increase in operating cost (i.e., if this policy increases overall operating profit). The extent to which a change in elapsed time affects passenger itinerary choice–-and thus an airline's market share–-is analyzed. An existing airline itinerary choice survey is extended to test the assumption that passenger demand is affected by the length of connecting times. Previous studies have not explicitly focused on the connecting time at hubs in their models. The hypothesis is that passengers might incur lower utilities from shorter connecting time versus longer connecting times based on the potential discomfort of a hasty connection and the misconnection risk associated with short connecting times. A stated preference experiment is performed, and socioeconomic data are collected to estimate a choice model. Multinomial logit model results support this hypothesis and refute the traditional network airline assumption.
Evolution of U.S. Domestic Airline Route Networks since 1990
Authors: Oster Clinton V. , Strong John S.
Published: May 2018

This paper examines how the networks of both legacy airlines and low-cost carriers evolved and adjusted to the changing competitive and economic environment between 1990 and 2003. The route networks of Air-Tran, America West, American, Continental, Delta, JetBlue, Northwest, Southwest, United, and US Airways are examined. Several measures of operational characteristics are developed and applied to the principal hubs and other dominant airports of each of these carriers. Particular attention is paid to the strategic use of regional jets operated by affiliated carriers and the extent to which passengers used connecting flights as opposed to direct flights. The analysis focuses on how these airlines adapted their use of hubs and route networks during periods of economic growth and recession and how they adapted to other changes in the competitive environment. The legacy airlines have not backed away from the traditional hub-and-spoke network, nor is there evidence of reduced emphasis on connecting traffic. Instead, the dominant change was a dramatic increase in the role of regional jets flown by affiliated carriers in their primary hub airports. The use of regional jets allowed the major airlines to increase the number of aircraft departures and the number of cities served from their hubs between 2000 and 2003 when faced with a reduced number of passengers.
Business-to-Business Electronic Marketplaces in the Airline Industry
Authors: Smyth Austin , Wagner Claudia-Maria
Published: May 2018

Airlines in all strategic sectors are experiencing ever-increasing competitive pressures. This paper focuses on the impact of business-to-business electronic marketplaces (e-marketplaces) on efficiency improvements. Of all airlines, 65% report using e-marketplaces in procurement operations. However, airlines’ initiation and financial involvement in e-marketplaces is low. Low-cost airlines have taken the lead in using e-marketplaces in non-maintenance-related areas, and full-service airlines use them less often across all spending categories. Spares and repairs, office supplies, and tools and ground support equipment show the greatest potential for reducing costs and increasing efficiency. Airlines involved in strategic alliances exhibit greater levels of use of e-marketplaces than other airlines. Competitive pressures contribute to the urgency of the search for new tools to realize incremental cost savings. It is evident that e-marketplaces are one such tool, a lesson already well-appreciated by the low-cost sector.
Model of Ultimate Capacity of Dual-Dependent Parallel Runways
Authors: Janic Milan
Published: May 2018

This paper develops an analytical model of the ultimate capacity of dual-dependent parallel runways (with close or intermediate spacing), where ultimate capacity is defined as the maximum number of aircraft accommodated during a given period (usually 1 h or 15 min) under constant demand for service and other given conditions. The model uses six inputs: geometry (configuration) of parallel runways; air traffic control (ATC) separation rules; technologies for aircraft primary navigation, communication, and air traffic surveillance, which influence separation rules and the degree of dependency of two runways; aircraft fleet mix in terms of wake–vortex categories and approach and departure speeds; proportion of arrival and departure demand; and ATC tactics of sequencing particular aircraft types and operations. The output represents the so-called capacity coverage curve, which reflects different scenarios of using given runways. The model is used to calculate the capacity of a large European airport.
Recommendations for Stabilization of High-Sulfate Soils in Texas
Authors: Harris Pat , von Holdt Joré , Sebesta Stephen , Scullion Tom
Published: May 2018

In an effort to construct roads more quickly, high-plasticity index soils stabilized with lime are now routinely compacted the day after mixing. With this practice has come an increasing number of heaves due to soluble sulfates reacting with the lime to form ettringite. Soils with sulfate concentrations below 7,000 to 8,000 parts per million (ppm) can generally be treated with lime. This research was performed to identify stabilizers that can be used with sulfate concentrations above 10,000 ppm. The effectiveness of the stabilizers was determined by the measurement of three-dimensional (3-D) swell reduction and unconfined compressive strength. The researchers evaluated 12 stabilizers, including enzymes, polymers, acids, emulsions, fly ash, and ground granulated blastfurnace slag (GGBFS). Three stabilizers significantly reduced volumetric swell. A polymer and an acid reduced swell by about 8%. GGBFS plus lime reduced swell by 10%. GGBFS plus lime was the only stabilizer that reduced swell, increased strength, and was cost-effective enough for the Texas Department of Transportation to consider as an alternative to lime in high-sulfate soils.
Assessing the Quality of Soils Modified with Lime Kiln Dust
Authors: Daita Radha Krishna , Drnevich Vincent P. , Kim Daehyeon , Chen Renpeng
Published: May 2018

By-product materials such as lime kiln dust (LKD), cement kiln dust, and fly ash are used for modifying pavement subgrades. It is insufficient to use density and water content measurements for compaction quality control on modified soils where chemical reactions occur because the properties of the modified soil differ from those of the parent materials. The amount of lime, the clay mineralogy, the soil water content, and the percentage fines in the soil are important parameters that affect the compaction behavior and subsequent properties of the modified soil. Hence, they should be considered for effective quality control. The behavior of soils modified with LKD is more complex than that of soils modified with lime because of the presence of various compounds besides lime in LKD. Research indicates that the electrical conductivity of soil is strongly affected by chemically modifying soils and tracks the chemical reactions with time. Time domain reflectometry (TDR) technology using the Purdue TDR apparatus measures the electrical conductivity of soil and is feasible for use in the laboratory and in the field. This paper describes the electrical conductivity behavior of an LKD-modified soil for various compaction conditions. The variation of electrical conductivity with time for a given cohesive soil is shown to depend on the amount and type of LKD and the water content. A hyperbolic-type model is proposed to capture the change in electrical conductivity with time for different amounts of LKD. Test results indicate that electrical conductivity also can be correlated to the penetration resistance of modified soil, which is an indicator of shear strength. Compared with conventional test methods, TDR is expected to provide better understanding of the rate and extent of chemical reactions between chemical modifiers such as LKD and soil and be useful for compaction quality control.
In-Vehicle Data Recorder for Evaluation of Driving Behavior and Safety
Authors: Toledo Tomer , Lotan Tsippy
Published: May 2018

This paper describes the overall framework and components of an in-vehicle data recorder (IVDR) called DriveDiagnostics and presents results from a study to validate its performance. This IVDR has been designed to monitor and analyze driver behavior not only in crash or precrash events but also in normal driving situations. It records the movement of the vehicle and uses this information to indicate overall trip safety. A validation study involved 33 drivers whose vehicles were instrumented with the IVDR. The experiment first included a blind profiling stage in which drivers did not receive any feedback from the system; that stage was followed by a feedback stage in which drivers had access to personal web pages with the information recorded by the system. Data collected in the blind profiling stage was used to investigate the connection between driver safety indices as captured by the system and historic crash data. The results show significant correlations between the two data sets, suggesting that the driving risk indices can be used as indicators of the risk of involvement in car crashes. This connection enabled investigation of the potential impact of the system on driving behavior and on safety. The results show that the initial exposure of drivers to the system has a significant positive impact on their behavior and on safety. Access to the feedback provided by the system has further impact on driver performance. However, if follow-up efforts are not made, neither of these positive impacts is sustained over time.
Analysis of Factors Affecting the Severity of Head-On Crashes
Authors: Deng Zuxuan , Ivan John N. , Gårder Per
Published: May 2018

The National Center for Statistics and Analysis and NHTSA suggest that head-on crashes are disproportionately represented in fatal crashes on two-lane highways, which constitute a substantial proportion of the highway network in the United States. This study focuses on analysis of the statistical association between head-on crash severity and potential causal factors, such as the geometric characteristics of the road segment, weather conditions, road surface conditions, and time of occurrence. Ordered probit models were estimated for data sets describing two-lane roads in Connecticut between 1996 and 2001. It was found that a wet roadway surface and narrow road segments were significantly related to more severe head-on crashes. A high density of access points and a nighttime occurrence of the crash were significantly related to more severe cases. Pavement width was found to be the most consistent factor, possibly because a wider road offers more space to avoid a direct head-on impact, thus reducing the severity of the crash. In addition, vehicle braking performance was important, as suggested by the higher probability of more severe head-on crashes on wet surfaces. The analysis results may be used by practitioners to understand the trade-off between geometric design decisions and head-on crash severity. Furthermore, identification of related factors will help to better explain crash phenomena and in turn to institute safer roadway design standards.
Iowa's Experience with Road Diet Measures
Authors: Pawlovich Michael D. , Li Wen , Carriquiry Alicia , Welch Tom
Published: May 2018

A before-and-after study implemented from a Bayesian perspective to assess crash history reduction due to road diets in Iowa was conducted by the Iowa State University Department of Statistics in cooperation with the Iowa Department of Transportation's Office of Traffic and Safety. The study used both monthly crash data and estimated volumes obtained from TAS for 30 sites—15 treatment and 15 comparison—over 23 years (1982 to 2004). The sites had volumes ranging from 2,030 to 15,350 during this period and were largely located in smaller urbanized areas. The research objective was to assess whether road diets appear to result in crash reductions on Iowa roads. Crash data were analyzed at each site before and after the conversions were completed. Given the random, rare nature of crash events, a hierarchical Poisson model was fitted, such that log mean rate was expressed as a piecewise linear function of time period, seasonal effects, and a random effect corresponding to each site. Monthly traffic volumes were incorporated as exposures. Estimation of model parameters was conducted within a Bayesian framework. Results indicate a 25.2% reduction in crash frequency per mile and an 18.8% reduction in crash rate. This differs from a previously publicized study that reported a 6% reduction in crash frequency per mile and an insignificant indication for crash rate effects. The results from the Iowa study fit practitioner experience and agree with another Iowa study that used a simple before-and-after approach on the same sites.
Financing Road Networks in Developing Countries
Authors: Agosta Roberto D.
Published: May 2018

During the 1960s and 1970s, developing countries received enormous loans from multilateral credit organizations and funds from developed countries to finance highway projects, mainly the paving of highways and the opening of natural surface roads to mobilize production. Traditionally, each loan required a cost–benefit analysis showing that the benefits of the project exceeded its costs in terms of vehicle operating expenditures, time savings, accident reduction, and so forth. Unfortunately, many projects have been used as political drivers, and once the projects were initiated, not enough funds were allocated for maintenance and reconstruction. As a result, the roads have deteriorated; thus transportation costs increased and ultimately the theoretical benefits of the original project were negated. In this paper, the author explains that just as important as the ex ante estimation of benefits of a project is that governments guarantee the resources needed to maintain and conserve the roads built and thereby close the “virtuous circle” between the economic benefits foreseen in the ex ante evaluation, the use of the highway, and its financing through different mechanisms.
Transportation Implications of Land Development in a Transitional Economy
Authors: Yang Jiawen
Published: May 2018

This research reveals and quantifies the transportation impacts of the changing workplace–residence relationship stemming from land and housing reforms in Chinese cities, with Beijing as the study case. Evidence from a 1996 housing relocation survey indicates that commuting time increases by 30% as households move away from previous housing locations and from central districts to suburban districts. This finding partially explains the demand for motorized transportation and the congestion in today's Chinese cities. The research also reveals the importance of urban growth strategies in preventing congestion from worsening as urban growth continues.
Analysis of Security System Designs for Ferry Transportation
Authors: Leone Kelly , Liu Rongfang (Rachel)
Published: May 2018

In detecting threats, particularly explosives, the challenge is to design a system with acceptable detection probability and false-alarm rate that does not unduly inconvenience travelers. Ferry passengers, in particular, are less likely than aviation passengers to tolerate extra delays for extensive scrutiny of themselves or their personal belongings. Similarly, substantial purchase and deployment costs of equipment by ferry owners and operators would not be tenable for small improvements in security. Thus, this paper analyzes different approaches to security and how best to combine detection capabilities and people to enhance ferry transportation security without affecting mobility. Several factors must be considered in choosing practical combinations of detectors to provide the best possible security system. Those factors and their interrelationships are examined within the context of different architectures. Besides the throughput analysis, the manuscript presents a general framework to compare security system designs and implement efficient and effective alternatives for ferry transportation.
Comparison of Emissions from Light Rail Transit, Electric Commuter Rail, and Diesel Multiple Units
Authors: Messa Christina A.
Published: May 2018

The United States is experiencing a revival of interest in diesel multiple-unit (DMU) passenger railcars. At the same time, communities are questioning whether diesel makes good sense as they compare the diesel multiple unit with electric rail modes such as light rail or electric multiple units. This study quantifies the emissions into a region from diesel multiple units and the electricity generation for electric rail modes, for oxides of nitrogen (NOx), an ozone precursor; particulate matter (PM); volatile organic compounds (VOCs), another ozone precursor; carbon monoxide (CO); and carbon dioxide (CO2). The study found that emissions attributable to electric rail modes are highly variable and depend on the cleanliness of the electricity generated. The dirtiest electricity pollutes orders of magnitude more than the cleanest. The study conclusion is that emissions from diesel multiple units and electric rail modes are not dramatically different on a per seat mile basis and that the exact comparison will depend on the cleanliness of the electricity generation and the type of diesel multiple unit consist. When compared on a per seat mile basis against electric rail modes using the average electricity generated in the United States, DMUs emit about the same amount of PM, equal or greater amounts of NOx, more CO and VOCs, and less CO2. The study also concludes that the rapidly changing diesel engine emissions standards will result in DMUs being introduced within the next 6 years with PM and NOx emissions that are nearly as low as the cleanest electricity generation today.
Designing Bus Rapid Transit for Light Rail Transit Convertibility
Authors: Wood Eva , Shelton David S. , Shelden Matt
Published: May 2018

This paper focuses on considerations that should be included in the design of a busway–bus rapid transit (BRT) facility for future conversion from BRT to light rail transit (LRT). A selection of BRT and LRT projects in North America and overseas were reviewed to assess the current industry practice in relation to BRT conversion to LRT. Most BRT projects reviewed for this study contain some provisions for future conversion to LRT. However, other than the current project to convert the downtown Seattle, Washington, transit tunnel, no known conversions from BRT to LRT have occurred. Design elements that should be considered when the cross section for a project is determined include vehicle type (LRT, bus, guided bus) and the operational configuration (barrier separation, mixing of buses with general-purpose and high-occupancy vehicle traffic, etc.). Finally, the construction activities required for conversion depend on whether the BRT system was designed and constructed to include provisions for LRT. Such activities can involve modification to both the main line and stations. If no provisions for LRT were part of the busway design and construction, the cost of conversion can be significantly higher due to the need for more extreme modification or total reconstruction of structures and other facilities.
Pedestrian and Motor Vehicle Traffic Control Practices for Light Rail Transit
Authors: Farrán José I.
Published: May 2018

The focus of this paper is to provide an informative summary on innovative pedestrian and motor vehicle traffic control designs and practices that have been applied to the recently opened light rail system in Barcelona, Spain. In April 2004 Barcelona, the capital of the Catalunya region, opened a completely new light rail system to expand and support its extensive subway, bus, and commuter rail system. Known locally as the Trambaix and Trambesòs, these two light rail lines operate within a broad range of urban environments, both on street and in semiexclusive rights-of-way. Accommodating light rail in these multiple environments while maintaining or improving safety has led local transportation planners and engineers to use a variety of innovative traffic control practices to manage conflicting movements with LRVs and to provide motorists, as well as pedestrians and bicyclists, with better information on which to base their decisions. This paper, based on the author's site visits and technical discussions with local planners and engineers, summarizes these practices and identifies those that could have the greatest potential for implementation in the United States.
Moving Driverless Transit into the Mainstream
Authors: Cottrell Wayne D.
Published: May 2018

Driverless transit features vehicles or transit units functioning with no onboard intervention from a driver or attendant. In comparison with traditional transit, driverless transit offers reduced labor costs and smaller vehicles, albeit with higher capital costs, and better performance records. As of 2005 there were 37 driverless transit systems in urban service, with five in the United States. Fifteen cities in Canada, Europe, and East Asia had driverless metros. To move driverless transit into the mainstream, research is needed in multiple areas. This paper examines research needs identified in 12 papers presented at the 10th International Conference on Automated People Movers (APMs), with supplemental information from related literature. Integrating APMs into airport security infrastructure, the development of lightweight materials for vehicles and guideways, and personal rapid transit (PRT) reliability and systems theory are among the high-priority research challenges. Medium-priority research needs would focus on special applications of and revenue generators for driverless transit. Although a great deal of driverless transit research has been conducted in simulation, there is a need for operating and performance data from existing systems. These data would enable driverless transit to be considered in modal alternatives analysis. Also, to bring concepts such as PRT into reality, full-scale models need to be tested in operational environments. It is argued that research supported by industry and local agency consortiums can make incremental advancements, but extensive studies require committed, high-level government funding. While the development of driverless transit in the United States has been stifled by high-profile cost overruns and abandonments, successful applications in Europe or elsewhere may revive domestic investment. Potential driverless transit research funding resources are suggested.
Service Reliability and Hidden Waiting Time
Authors: Furth Peter G. , Muller Theo H. J.
Published: May 2018

Traditional transit service quality measures separate waiting time from service reliability and thereby underestimate the real cost of waiting and fail to evaluate the effect of unreliability on passengers. This study's analysis of passenger behavior shows that, for short headway service, the cost of waiting involves not only the mean time spent waiting on the platform but also potential waiting time, that is, the additional time that passengers have to budget for waiting. Budgeted waiting time is based on an extreme of the waiting time distribution such as its 95th percentile value, which is extremely sensitive to service reliability. Methods for determining the distribution of passenger waiting time from automatic vehicle location (AVL) data are derived. For long headway service, actual and budgeted waiting times are shown to be related to high and low extremes of the schedule deviation distribution, which can likewise be determined from AVL data. Two other components of long headway waiting, schedule inconvenience and synchronization cost, are also analyzed. Waiting cost functions and waiting time measures that account for both headway and service reliability are developed and are harmonized in a framework that provides a smooth transition from short to long headway waiting. Examples show how service reliability can be measured as a waiting cost and how service reliability improvements can reduce waiting cost as much as a large reduction in headway can.
Speed Index
Authors: Evanchik Daniel M. , Best Matthew G. , Smith Brian L. , Scherer William T.
Published: May 2018

Given the increased emphasis on transportation system operations, transportation agencies require effective operations performance measures. The purpose of the present research effort was to develop and explore the utility of a simple system operations performance measure that meets the following criteria: (a) it is measurable given current sensor deployment, (b) it is understandable to a wide range of individuals, (c) it is applicable on different functional classes of roadways, (d) it is scalable from the lane level up to a regional or statewide measure, and (e) it is independent of major assumptions or estimation techniques. The measure proposed and explored in this paper, the speed index, can be defined as the volume-weighted percentage of the speed limit at which a roadway location, zone, corridor, or even a region operated for a given time period. This measure was demonstrated to be effective in supporting numerous operations analysis activities, including an analysis of seasonal variations in traffic and an in-depth analysis of a single incident's impact on regional conditions. On the basis of the case study presented, it is concluded that the speed index is a viable measure that can be used to support state operations programs.