bluuebunny/crossref_metadata_2025 huggingface dataset:
Characteristics of Passing and Meeting Maneuvers on Exclusive Bicycle Paths
Authors: Khan Sarosh I. , Raksuntorn Winai
Published: April 2007

The findings are presented of a comprehensive analysis of the characteristics of passing and meeting maneuvers of bicycles traveling on an exclusive bicycle path 3 m (10 ft) wide. The study is based on bicycle location data collected every 0.5 s from video images of bicycle traffic scenes recorded in Denver, Colorado. For passing maneuvers, the average speeds of passing and passed bicycles, the relationship between passing and passed bicycle speeds every 0.5 s, comfortable speed difference threshold, lateral spacing during passing, average passing lengths, and the shape of passing are reported. For meeting maneuvers, statistics about the average speed and lateral spacing are included; for paired riding, headway and lateral spacing statistics are included. The results also show that the average bicycle speeds estimated are significantly higher than the speeds reported from a study conducted in the Netherlands. These findings can be used to develop more accurate procedures for the analysis of the quality of service of bicycle paths. According to the 2000 Highway Capacity Manual (HCM), a weighted sum of the number of passing and meeting events is used as the criterion to determine the level of service for bicycle paths. The procedures in the 2000 HCM are based on research mainly conducted in the Netherlands for two-lane or 2.4-m-wide bicycle paths and have been extended to 3-m-wide paths. The findings presented here are for 3-m-wide bicycle paths in the United States and therefore may be used to develop new procedures for HCM as well as provide the data needed to develop a bicycle simulation model.
Interval Distribution for Exclusive, Mixed-Use Bicycle Paths
Authors: Khan Sarosh I. , Singh Bhuvanesh
Published: April 2007

The interval distribution for exclusive, mixed-use bicycle paths that include pedestrians, skaters, and joggers is examined. Interval distributions are used to generate arrivals, an essential input to a traffic simulation model. Different time headway distributions have been fitted for vehicular traffic flow based on the type of facility, traffic composition, and flow rate. However, only one study reports on the arrival patterns of bicycles approaching an intersection, and no studies examine the interval distribution for bicycles on exclusive bicycle paths. Bicycle traffic data collected for two bicycle paths in Denver, Colorado, were analyzed. Two populations were considered to describe arrival patterns on bicycle paths. The first consisted of the combined population of bicyclists, pedestrians, skaters, and joggers. The second population consisted of only bicycles, which are considered separately. With bicycles classified as unconstrained and constrained in either a combined population of bicyclists, pedestrians, skaters, and joggers or a separate population of bicyclists only, a Schuhl’s composite distribution of negative exponential distribution was found to model interval distributions. The composite distribution’s fit was significantly better than a negative exponential distribution, as demonstrated by Kolmogorov-Smirnov tests. The distributions may be used to generate not only the interval between consecutive arrivals but also the type of user.
Spatial Microassignment of Travel Demand with Activity Trip Chains
Authors: Abdelghany Ahmed F. , Mahmassani Hani S. , Chiu Yi-Chang
Published: April 2007

As activity-based approaches gain acceptance for travel demand analysis and forecasting in practice, the unit of analysis in transportation planning models needs to shift from a one-way trip to an activity schedule with associated trip chains. A spatial network assignment process and its application to an actual network are described; the process can be used in conjunction with activity-based travel demand forecasting procedures as well as for traffic operational studies. Two simulation-based dynamic spatial microassignment procedures for travel demand with activity trip chains are presented. The first represents a one-step simulation-assignment procedure in which assignment of trips is based on prevailing travel time. The second is an iterative simulation-assignment procedure in which a user equilibrium solution is obtained. The models are illustrated through various experiments conducted using an actual network (in Fort Worth, Texas) to examine network performance under different activity and trip-chaining scenarios. Different demand levels with different trip chain patterns are considered and compared for an actual transportation network. In addition, a case is made for dynamic microassignment of activity trip chains by contrasting it with current practice and illustrating the pitfalls of inappropriately recognizing trip chains using current-practice assignment. In particular, two different procedures are considered and compared for selected test scenarios with the dynamic assignment models presented. The first procedure corresponds to the case in which the activity and trip-chaining behavior is completely ignored, and only the final destination in the chain is considered. The second procedure treats the links of the chains separately as independent trips, without appropriate linkage between them.
Activity Patterns of Canadian Women: Application of ClustalG Sequence Alignment Software
Authors: Wilson Clarke
Published: April 2007

Sequence alignment procedures and a new software package for creating multiple sequence alignments, called ClustalG, are described and used to identify the activity patterns of Canadian women. ClustalG eliminates the constraint on the size of the event classification system implemented in software developed for biological applications, and this feature allows an analysis of activity sequences in conjunction with their settings, in this example, location and the presence of other people. Work, weekend days, age, marital status, and the presence of children relate to membership in different activity-pattern groups. The addition of data on activity setting to the sequences changes the discriminatory power of the analysis. When the analysis omits settings, the daily activities of elderly women are grouped with weekend activities of younger, family-raising women. Inclusion of settings identifies the activities of elderly women largely on the basis of location at home and isolation from other people. ClustalG is freely available over the Internet at www.stmarys.ca/partners/iatur/clustalG.
Incorporating Safety and Security Issues in Urban Transportation Planning
Authors: Chatterjee Arun , Wegmann Frederick J. , Fortey Nicholas J. , Everett Jerry D.
Published: April 2007

The Transportation Equity Act for the 21st Century specifically mentions safety and security as making up one of the seven factors to be considered as metropolitan planning organizations (MPOs) develop their transportation plans and programs. In order to assess the current practice, visits were made to several MPOs and transit districts around the country to learn how safety and security were being addressed in both the long-range and short-range transportation planning processes. Although safety and security were reflected in planning policies and goals and short-range project selection and programming incorporated measures of safety and security, there were few instances in which long-range planning incorporated these issues. In many cases the lack of data and limited analysis tools resulted in a reliance on subjective assessments of safety and security issues. The findings from the case study-oriented project are documented.
Transportation Planning and TRANSIMS Microsimulation Model: Preparing for the Transition
Authors: Rilett L. R.
Published: April 2007

The Transportation Analysis and Simulation System (TRANSIMS) was developed as a replacement for the four-step travel demand model. The goal was to provide a simulation system that could analyze issues facing transportation planners such as sustainable development, environmental impacts of proposed projects, and intelligent transportation systems deployment. Because TRANSIMS represents a significant shift from the current state of the practice, the transportation planning community will need to spend significant human and capital resources preparing for the transition. Some insight into these transitional issues is provided on the basis of lessons learned from research on actual calibrated transportation networks in Texas. An overview of TRANSIMS in terms of its main components along with a brief comparison with the four-step model are supplied, followed by a discussion of the data requirements with specific reference to the current data needs associated with the four-step model. The challenges inherent in converting databases that have been developed for four-step models are also discussed on the basis of the conversion of existing traffic network files. Next, the TRANSIMS traffic flow theory is described, and the challenges for transportation planners are illustrated using calibrated networks from two highway corridors in Houston, Texas, and one diamond interchange network in College Station, Texas. Last, the capabilities of TRANSIMS with respect to output analysis are described.
Analysis of In Situ Horizontal Joint Movements in Rigid Pavements
Authors: Woo Lee Seung , Stoffels Shelley M.
Published: April 2007

Doubts about the reliability of the AASHTO model for predicting rigid pavement joint openings have arisen from a number of researchers on the basis of the observation of significant differences in average in situ measurements from AASHTO predictions. Considerable variation of the magnitude of the joint movements in a given pavement section has also been noted. Previous attempts to determine a linear relationship between joint movement and temperature change could not provide a statistically sound linear relationship because of considerable unexplained scattering. Understanding the patterns of in situ joint movement for various pavement conditions provides valuable information for understanding the cause of the persistent controversy over the effectiveness of joint sealing and its effects on pavement performance and provides many of the necessary inputs for development of a reliable probabilistic joint movement prediction method. A systematic procedure to analyze joint movement data is suggested. Based on the suggested method, the effective ratios of joint movement to change in temperature for 16 pavement sections included in the long-term performance pavement seasonal monitoring program are presented. The causes of scattering and erratic movements are identified and isolated, and a strong linear relationship has been obtained.
Modeling of Jointed Plain Concrete Pavement Fatigue Cracking in PaveSpec 3.0
Authors: Khazanovich Lev , Yu H. Thomas
Published: April 2007

An improved fatigue cracking model is presented for jointed plain concrete pavements (JPCP) incorporated in PaveSpec 3.0. PaveSpec 3.0 is the latest version of the software developed under the FHWA project on performance-related specifications (PRS) for concrete pavements. The ability to accurately predict pavement distresses is important for successful implementation of PRS. The development process for the JPCP fatigue cracking model is described and the final model is presented along with the procedure used to calculate fatigue damage. The new JPCP cracking model has reasonable statistics for being calibrated with such a large number of data points (815) and is deemed suitable for use with the current PRS procedure. Specific improvements to the new model include direct consideration of the characteristics of the base layer, direct consideration of the effects of a tied portland cement concrete shoulder, incorporation of improved procedures for computing load and thermal curling stresses, incorporation of the influence of built in construction curling on slab cracking, and recalibration of the model by using a database that is much improved in both quality and quantity.
AASHTO Drainage Coefficients for Flexible Pavements
Authors: Richardson David N.
Published: April 2007

A method for determining AASHTO drainage ( m) coefficients for flexible pavements is presented. In essence, m coefficients were developed as ratios of the layer coefficients of the AASHO road test granular base material under any given drainage and climate condition to the layer coefficient of the road test base material under road test site conditions. The layer coefficients were calculated from resilient moduli determined for various conditions by use of elastic layered analysis. The moduli were varied by changing subgrade and base moisture conditions for any given time of year. The base material moisture sensitivity (effect on θ model constants k1 and k2) was determined, in part, by the resilient modulus laboratory testing of granular materials. The result of the preceding analysis was the creation of a set of tables that guide the designer to a choice of m coefficients. The new m values can be used to provide a rational measure of the influence of pavement drainage on pavement performance.
Flexible Pavement Design in Michigan: Transition from Empirical to Mechanistic Methods
Authors: Harichandran Ronald S. , Buch Neeraj , Baladi Gilbert Y.
Published: April 2007

Michigan is rapidly moving toward adopting and using a mechanistic-empirical design for flexible pavements. To facilitate the transition from empirical to mechanistic design methods, the Michigan Department of Transportation contracted the development of software called the Michigan Flexible Pavement Design System (MFPDS). This software provides a holistic framework for analyzing and designing flexible pavements. MFPDS includes modules for AASHTO design, linear and nonlinear mechanistic analysis, backcalculation, and mechanistic design (including overlay design). The software incorporates enhanced elastic layer and finite element models within an easy-to-use Windows user interface and can be used on a routine basis. New response models to predict fatigue life and rut depth also were developed as part of this effort and are included in MFPDS. New pavements and overlays may be designed to limit predicted distresses to user-specified threshold values. The features of the mechanistic analysis and design approaches used are presented.
Layer Thickness Variability for Flexible Pavements in North Carolina
Authors: Corley-Lay Judith , Morrison Clark S.
Published: April 2007

Ground-penetrating radar (GPR) was used to identify the variability in layer thickness for 13 general pavement study sites in North Carolina. Two data sets were collected for each of 11 sites and one data set was available for 2 additional sites. Asphalt thicknesses varied over a wide range, but the standard deviation for asphalt layers less than 6 in. (15.24 cm) thick was 1 or less. GPR results were consistent with North Carolina typical base course thicknesses, whether that base be asphalt, dense-graded aggregate, or cement-treated aggregate. Variability in base course thickness was greater than variability in the surface layer. The effects of changing layer thicknesses from the mean thicknesses to the mean 1 standard deviation were examined by backcalculation and by calculating overlay thickness requirements with the North Carolina Department of Transportation overlay design procedure. Overlay thickness requirements typically changed by 3.8 mm (0.15 in.) over the range of layer thicknesses. Backcalculated moduli for asphalt and aggregate base were found to be most affected when the asphalt layer is thinner and the base course standard deviation is large. It is concluded that it is important to have an estimate of layer thicknesses for overlay design but that extensive coring is not required to obtain an adequate estimate.
Propagation Mechanisms for Surface-Initiated Longitudinal Wheelpath Cracks
Authors: Ann Myers Leslie , Roque Reynaldo , Birgisson Bjorn
Published: April 2007

Field observation of cores and trench sections extracted from asphalt concrete highway pavements exhibited propagation of surface-initiated longitudinal wheelpath cracks. The initiation for these cracks was explained by high-contact stresses induced under radial truck tires; however, the mechanisms for surface crack propagation have not been explained. A combination of finite element modeling and fracture mechanics was selected for physical representation and analysis of a pavement with a surface crack. An approach was developed to model a cracked pavement and predict pavement response in the vicinity of the crack and throughout the depth of the asphalt layer. Analysis of pavement response indicated that the mechanism for crack propagation was primarily tensile. Shear stresses were not significant to control crack growth, regardless of load position. Effects of pavement structure and load spectra (magnitude and position) were evaluated in a comprehensive parametric study of the cracked pavement. Load positioning had the most effect on crack propagation, along with asphalt and base layer stiffness. The direction of crack growth was computed and changed with increased crack length. Therefore, identification of a tensile failure mechanism for crack propagation was accomplished, along with demon stration of the importance of defining load spectra and inspection of the change in direction of crack growth. Most important, the defined mechanism offered an explanation for crack propagation and confirmed observations of crack growth in the field.
Effects of Interface Condition and Horizontal Wheel Loads on the Life of Flexible Pavement Structures
Authors: Romanoschi Stefan A. , Metcalf John B.
Published: April 2007

The effects of interface condition and horizontal wheel loads on the life of flexible and semirigid pavements were determined. The methodology consisted of implementing a previously derived interface constitutive model into the ABAQUS finite element program to compute the stresses and strains in typical flexible and semirigid road structures. The Shell transfer functions for fatigue cracking and terminal serviceability were used to estimate the life of the two pavements. The study revealed that the horizontal loads acting at the pavement surface lead to dramatically increased tensile strains at the top and bottom of the wearing course and at the top of the binder course. This may justify the initiation of cracking at the surface of the pavement and not at the bottom of the asphalt layer, as generally assumed. For semirigid pavements, the condition of the wearing-binder course interface affects the strains in the wearing course, whereas the condition of the binder-base interface affects the horizontal strain field in the binder layer more as well as the vertical strains at the top of the subgrade. For flexible pavements, the condition of the interface between the wearing and binder courses dramatically changes the strain field in the wearing and binder layers and increases the vertical strains at the top of the granular base and subgrade layers. The cumulative effect of the interface condition and horizontal forces acting at pavement surface is expressed by a dramatic reduction in pavement life, especially for the semirigid pavement.
Use of Long-Term Pavement Performance Data for Calibration of Pavement Design Models
Authors: Hajek Jerry J. , Kazmierowski Thomas J.
Published: April 2007

The benefits of long-term pavement performance data for calibration of the AASHTO flexible pavement design model for Ontario conditions are documented. To ensure that the AASHTO-Ontario pavement design model reflects Ontario pavement design practice and matches the observed pavement performance, long-term pavement performance data for 65 flexible pavement sections were used. Thirty-nine sections had original construction, and 26 sections received one rehabilitation treatment (overlay). The data for each section included the type and thickness of paving materials, subgrade type, pavement performance, and traffic loads. The results of the calibration and verification process indicate that for new flexible pavement design the AASHTO-Ontario model yields results that are in good agreement with the observed pavement performance. For overlays, there was a large difference between the predicted and observed performance. This indicates that considerably more observations (pavement sections) are required for assessment of rehabilitation designs than for the original construction because the overlays are not always built for structural reasons only. Possible avenues for using long-term pavement performance data to establish the values of input parameters such as structural layer coefficients and modulus of subgrade are also described. Even relatively limited long-term pavement performance data provide valuable information for the calibration and verification of pavement design methods.
Modeling Driver Behavior by Using Mind’s Eye Coordinates
Authors: Fancher Paul S. , Bareket Zevi , Bogard Scott
Published: April 2007

Concepts are presented that are suitable for use in modeling and understanding the driving process. Attention is focused on modeling driver control of forward speed and the range gap between vehicles. The structure of the model is based on psychological concepts associated with knowledge-, rule-, and skill-based behavior. The model uses variables representing features of the forward scene as projected onto the driver’s retina. These variables are referred to as mind’s eye coordinates. For example, driver perceptual motor skills, as used for increasing or decreasing speed, are expressed by variables associated with looming effects for moving and stationary objects as well as streaming effects associated with passing nearby stationary objects. Inequalities expressed in terms of mind’s eye coordinates are used in the model to identify signs that indicate to the driver which control rule to choose in various driving situations. The driving situations include closing on a slower-moving vehicle, following a preceding vehicle, braking in response to preceding vehicle deceleration, and accelerating. Examples show how the model works and compare its predicted results with measured manual driving performance in situations involving the control of the range gap to a preceding vehicle. Conceptual reasoning employing combined physical and psychological concepts is used to address issues associated with model validation.
Computational Techniques Used in the Driver Performance Model of the Interactive Highway Safety Design Model
Authors: Levison William H. , Simsek Ozgur , Bittner Alvah C. , Hunn Steven J.
Published: April 2007

The Interactive Highway Safety Design Model (IHSDM) is a high-priority research area for FHWA. IHSDM is a software system for evaluating the safety of alternative highway designs in a computer-aided design environment. The initial phase of this research program is to develop IHSDM for use in the design of two-lane rural highways. IHSDM includes a driver-vehicle module that simulates the moment-to-moment actions of a single driver-vehicle unit. Reviewed are the computational approaches that have guided the implementation of the driver performance model (DPM) that along with a vehicle model and other components constitute the driver-vehicle module. Five major computational functions of DPM are reviewed: perception, speed decision, path decision, speed control, and path control. Comparison of model results with data from a driving simulator demonstrates the ability of DPM to account for the horizontal curve deflection angle on the speed profile.
Asleep at the Wheel: Spatial and Temporal Patterns of Fatigue-Related Crashes in Honolulu
Authors: Kim Karl E. , Yamashita Eric Y.
Published: April 2007

As an island state located in the middle of the Pacific Ocean, where there is limited opportunity for long-distance driving, Hawaii provides an interesting context in which to study fatigue-related crashes. Data from the Hawaii Crash Outcome Data Evaluation System are used to analyze and map fatigue-related collisions. Injury outcomes of fatigue-related crashes are analyzed by using police crash data, emergency medical service records, and insurance claims records. There are distinct temporal and spatial patterns as well as relationships between fatigue-related crashes and driver characteristics. Recommendations for preventing fatigue-related crashes are developed. Roadway segments where fatigue-related crashes occur are identified as possible sites for various engineering treatments. Temporal and demographic information also can be used to design and implement more effective programs and systems for fatigue-related crashes.
Crash Rates and Traffic Maneuvers of Younger Drivers
Authors: Kirk Adam , Stamatiadis Nikiforos
Published: April 2007

Although the population of younger drivers has decreased over recent decades, their crash rates have increased. Research has associated their higher crash rates with societal influences and youthful behavior. Research was conducted to identify the specific driving maneuvers of which unsuccessful undertaking results in specific types of crashes involving younger drivers. Four types of crashes were identified as the most prominent for young drivers: intersection, rear end, passing, and single vehicle. The analysis was performed by examining the Kentucky crash database for the 1994-1996 period by using the quasi-induced exposure method. The results showed that for all crashes, there is a general trend of decreasing involvement with increasing age, which indicates that these drivers’ inexperience is the largest single contributor to their increased crash rates. Of significance is that for all crashes, a dramatic decrease of involvement after the first year of driving between the ages of 16 and 17 is observed. This may be indicative of a steep learning curve in the first years of driving regarding the ability to control a vehicle. Therefore, little can be done to improve this phenomenon. Increasing awareness among young drivers about these issues and their likely crash involvement appears to be the only viable approach. However, preliminary efforts from the graduated license program show that some trends have been reduced, indicating a possible influence on the crash rates of young drivers.
Safety-Restraint Use Rate as Function of Law Enforcement and Other Factors: Preliminary Analysis
Authors: White David J. , Washington Simon P.
Published: April 2007

Persistent use of safety restraints prevents deaths and reduces the severity and number of injuries resulting from motor vehicle crashes. However, safety-restraint use rates in the United States have been below those of other nations with safety-restraint enforcement laws. With a better understanding of the relationship between safety-restraint law enforcement and safety-restraint use, programs can be implemented to decrease the number of deaths and injuries resulting from motor vehicle crashes. Does safety-restraint use increase as enforcement increases? Do motorists increase their safety-restraint use in response to the general presence of law enforcement or to targeted law enforcement efforts? Does a relationship between enforcement and restraint use exist at the countywide level? A logistic regression model was estimated by using county-level safety-restraint use data and traffic citation statistics collected in 13 counties within the state of Florida in 1997. The model results suggest that safety-restraint use is positively correlated with enforcement intensity, is negatively correlated with safety-restraint enforcement coverage (in lanemiles of enforcement coverage), and is greater in urban than rural areas. The quantification of these relationships may assist Florida and other law enforcement agencies in raising safety-restraint use rates by allocating limited funds more efficiently either by allocating additional time for enforcement activities of the existing force or by increasing enforcement staff. In addition, the research supports a commonsense notion that enforcement activities do result in behavioral response.
Truck Driving Environments and Their Influence on Driver Fatigue and Crash Rates
Authors: Crum Michael R. , Morrow Paula C. , Olsgard Patricia , Roke Philip J.
Published: April 2007

The development of a typology of commercial vehicle driving environments, estimate of the percentage of drivers falling into each type of driving environment, and driving environment effects on driver fatigue are described. A model of commercial motor vehicle driver fatigue, based on literature sources and focus groups of industry professionals, is proposed. Three driving-environment factors (regularity of time, trip control, and quality of rest), comprising 25 indicators, are included in the model. Data were collected via a nationwide survey of 502 randomly selected over-the-road commercial truck drivers. Data analysis revealed 12 driving-environment indicators to be good predictors of fatigue and crash outcomes. Various 2×2×2 driving-environment typologies were created by using different high-low combinations of these 12 indicators. A typology based on the single best predictors of fatigue and crash outcomes from each driving-environment factor was selected for examination (i.e., favorable and unfavorable combinations of driving the same hours, waiting longer than expected for loads, and starting the workweek tired). The percentage of drivers working in each type of driving environment ranged from 5.2 percent to 20.1 percent. Additionally, the typology was significantly related to frequency of close calls and perceptions of fatigue. The 12 driving-environment indicators collectively accounted for 5 percent and 23 percent of the variability in close calls and fatigue perceptions, respectively ( p ≥ .001), and 2 percent of the variability in crash involvement ( p ≥ .07). Implications for fatigue management are also discussed.
Effectiveness of Truck Rollover Warning Systems
Authors: Baker Derek , Bushman Rob , Berthelot Curtis
Published: April 2007

Different types of intelligent rollover system deployed by road agencies across North America are investigated. The importance of weight is addressed for maximum effectiveness of rollover warning messages for commercial vehicles in a potential rollover situation on sharp curves or exit ramps. The type of information that may be used to activate a rollover is discussed to analyze the number of correctly warned vehicles compared with the number of false warnings generated by the rollover warning system. A case study of the effectiveness of an intelligent rollover system is presented. On the basis of this case study, it was found that speed-based rollover warning systems generated anywhere from 44 percent to 49 percent more false rollover warnings for commercial vehicles than did rollover warning systems that employed weight information in the rollover decision criteria.
Comparison of Collisions of Rigid Trucks and Articulated Trucks Against Road Safety Barriers
Authors: Giavotto Vittorio , Pernetti Mariano
Published: April 2007

Heavy vehicles used for road transport are essentially rigid trucks, rigid trucks with trailers, and articulated trucks. A collision of such a vehicle against a safety barrier has different outcomes, depending on the vehicle characteristics, even when the impact energy (Ie) is the same. The factors responsible for the different behavior of rigid and articulated trucks during collision are addressed. The study, carried out by computer simulation, was divided into three parts. The first part compared the overall behavior of the two types of vehicles during collisions to detect the most responsible factors. In the second phase, the single features that characterize each type of vehicle were tested. The third phase tried to define a relationship between the two types of vehicles. Results from Tests TB81 and TB71, established by the European Committee for Standardization 1317, were compared. The results show that a collision of an articulated truck is less severe than one of a rigid truck because of greater length, suspension stiffness, inertia, and configuration. However, the difference in behavior depends on kinetic Ie and side-friction coefficient (SFC). Four analytical expressions were found that relate Ies producing the same maximum transversal displacements or vehicle roll angle for the two types of vehicles. The study concerning the European tests on safety barriers shows that a hierarchy exists between them and it depends on the SFC.
Built Environment as Determinant of Walking Behavior: Analyzing Nonwork Pedestrian Travel in Portland, Oregon
Authors: Greenwald Michael J. , Boarnet Marlon G.
Published: April 2007

Much has been written about the connection between land use/urban form and transportation from the perspective of affecting automobile trip generation. This addresses only half the issue. The theoretical advances in land use–transportation relationships embodied in paradigms such as the jobs-housing balance, neotraditional design standards, and transitoriented development rely very heavily on the generation of pedestrian traffic to realize their proposed benefits. The present analysis uses models and data sets similar to those used in previous work for the Portland, Oregon, area but applies them toward analysis of nonwork walking travel. The results suggest that regardless of the effects that land use has on individual nonwork walking trip generation, the impacts take place at the neighborhood level.
Travel and the Built Environment: A Synthesis
Authors: Ewing Reid , Cervero Robert
Published: April 2007

The potential to moderate travel demand through changes in the built environment is the subject of more than 50 recent empirical studies. The majority of recent studies are summarized. Elasticities of travel demand with respect to density, diversity, design, and regional accessibility are then derived from selected studies. These elasticity values may be useful in travel forecasting and sketch planning and have already been incorporated into one sketch planning tool, the Environmental Protection Agency’s Smart Growth Index model. In weighing the evidence, what can be said, with a degree of certainty, about the effects of built environments on key transportation “outcome” variables: trip frequency, trip length, mode choice, and composite measures of travel demand, vehicle miles traveled (VMT) and vehicle hours traveled (VHT)? Trip frequencies have attracted considerable academic interest of late. They appear to be primarily a function of socioeconomic characteristics of travelers and secondarily a function of the built environment. Trip lengths have received relatively little attention, which may account for the various degrees of importance attributed to the built environment in recent studies. Trip lengths are primarily a function of the built environment and secondarily a function of socioeconomic characteristics. Mode choices have received the most intensive study over the decades. Mode choices depend on both the built environment and socioeconomics (although they probably depend more on the latter). Studies of overall VMT or VHT find the built environment to be much more significant, a product of the differential trip lengths that factor into calculations of VMT and VHT.
Internalizing Travel by Mixing Land Uses: Study of Master-Planned Communities in South Florida
Authors: Ewing Reid , Dumbaugh Eric , Brown Mike
Published: April 2007

Planners, public officials, and large-scale land developers increasingly promote mixed-use developments as an alternative to sprawl. They list among the benefits of such developments the “internal capture” of trips; that is, trips that would otherwise have filtered onto the regional road network will remain on site. Yet, so little information is available about internal capture rates that traffic impact studies for mixed-use developments become little more than exercises in speculation. In an attempt to advance basic knowledge of the subject and move toward better prediction methods, 20 mixed-use communities in south Florida were studied to determine the effect of land use mix on internal capture rates. The sample of communities studied had internal capture rates ranging from 0 to 57 percent of all trip ends generated. When modeled in terms of land use and accessibility variables, both the scale of a development and regional accessibility proved significant, with the former directly related to internal capture and the latter inversely related to internal capture. The bestfit model explained just under half of the variance in internal capture rates. Controlling for scale and regional accessibility, land use mix and density did not have independent predictive powers. Whether because of limitations of the data set, model specification, or method of analysis, the benefits of mixed-use development were not borne out.
Effect of Employment Site Characteristics on Commute Mode Choice
Authors: Shiftan Yoram , Barlach Yotam
Published: April 2007

Considerable effort has been made in recent years to resolve traffic congestion problems in metropolitan areas. The effects of employment site characteristics on commuting mode choice in the metropolitan area of Haifa, Israel, were studied. The analysis is based on trip diary data that included 4,794 commuting trips. In the first part of the investigation, the effect of different types of employment site on commuting mode choice was studied through aggregate analysis. In the second part, a four-mode multinomial model was developed. The results show a high rate of commuting by private vehicles in which the commuter is the driver. Commuters who have access to a private car are most likely to use it. High rates of commuting by bus are reported to employment sites located near the metropolitan central business district, local business employment sites, and areas with a high frequency of bus services. High rates of commuting by employer-provided transport were identified to suburban sites, industry sites, and areas with a low frequency of bus service. The research concludes that although automobile availability is the most important factor in mode choice, some employment site variables also have significant explanatory power.
Value of Different Categories of Information in Estimating Freight Origin-Destination Tables
Authors: Réos Alejandro , Nozick Linda K. , Turnquist Mark A.
Published: April 2007

An analysis to assess the value of information when freight origin-destination (O-D) tables are estimated is developed. The theory of design of experiments is used as a framework to ascertain the value of three categories of information: link counts, O-D totals, and aggregate O-D totals. On the basis of these insights, a forecasting model is developed for estimating the table quality to be obtained given the type and quantity of information used. Finally, the effect of introducing errors into the information is explored.
Identifying Multiple Reasonable Alternative Routes: Efficient Vector Labeling Approach
Authors: Park Dongjoo , Sharma Shyam Lal , Rilett Laurence R. , Chang Myungsoon
Published: April 2007

An exact approach for identifying multiple reasonable paths in a transportation network is proposed. It is motivated by the deficiencies of heuristic approaches and K-shortest-path algorithms that have been used historically. The proposed algorithm is based on the so-called efficient vector labeling approach. The search space is pruned using a resource constraint. A route constraint is applied for maintaining the reasonableness of alternative routes. In addition, a dominance-checking concept is introduced to avoid identifying candidate subpaths at nodes that cannot satisfy travel time or route uniqueness requirements. The approach was demonstrated on a transportation network from Austin, Texas. It was found that the proposed algorithm can efficiently identify multiple reasonable alternative routes in transportation networks and has a number of advantages as compared with traditional K-shortest-path algorithms and heuristic approaches.
Multiclass Continuous-Time Equilibrium Model for Departure Time Choice on Single-Bottleneck Network
Authors: Zijpp Nanne Van der , Koolstra Kaspar
Published: April 2007

Commuters may react to structural congestion on urban roads and freeways by adjusting their departure time. Single-bottleneck models enable direct insight into the mechanisms of departure time choice. The interaction of user equilibrium departure time choice processes for multiple user classes in continuous time is studied in the situation in which all users have to pass a common bottleneck. The study draws on the bottleneck approach introduced by Vickrey and provides a generic algorithm that solves the departure time choice equilibrium problem given heterogeneous departure time preferences, arbitrary origin-bound and destination-bound rescheduling cost functions, and arbitrary queuing cost functions. For all user classes, the (generalized) queuing costs have a travel duration–dependent component and a travel cost–dependent component. First, a solution is provided for the elastic-demand case. It is shown that the equilibrium departure rates per user class can be calculated directly by calculating the acceptable travel times per user class. Second, a solution is provided for the fixed-demand case. The fixed–demand problem is formulated as a minimization problem that is solved using the Nelder–Mead procedure. The algorithm is illustrated with an example showing the effects of a flat peak-hour road pricing scheme on the departure time choice and total incurred costs per user class.
Best Routing Policy Problem in Stochastic Time-Dependent Networks
Authors: Gao Song , Chabini Ismail
Published: April 2007

The best routing policy problem in stochastic and time-dependent networks is the subject of this study. This problem can be viewed as a counterpart of the shortest-path problem in deterministic networks. A stochastic time-dependent network is one in which the link travel times are random variables with time-dependent distributions. A routing policy is a decision rule that specifies what node to take next at each decision node on the basis of the realized link travel times and the current time. The framework of the problem is reviewed, on which basis one of the variants of the problem that are pertinent to the traffic context is studied. An exact algorithm to this variant is given, and its complexity is analyzed. Since the running time of the exact algorithm is generally exponential in the number of arcs, the importance of finding good approximations to the exact algorithm is pointed out. Several approximations are presented, and their effectiveness against the exact algorithm is studied both theoretically and computationally.
Study of Intersection Accidents by Maneuver Type
Authors: Mitra Sudeshna , Chin Hoong Chor , Quddus Mohammed Abdul
Published: April 2007

Studies dealing with the effect of road geometry on accidents by vehicle maneuvers have been reported, mostly for western countries and a few for Asia. However, no such studies have been reported for Singapore. Traffic accidents arising from head-to-side and head-to-rear maneuvers at four-legged signalized intersections in Singapore were investigated. Based on accident data at intersections in the southwestern part of Singapore from 1992 to 1999, the factors affecting such accidents were explored using zero-altered probability models. Specific roadway geometries as well as traffic control and regulatory factors that influence the two categories of accidents were identified. It was found that head-to-side accidents tend to decrease if there is an adjacent intersection within 200 m and if bus stops along the approach are provided with bays. On the other hand, longer sight distances and the presence of a pedestrian refuge tend to increase this type of accident. Higher speed limits were found to reduce the instances of zero head-to-side accidents. It was also found that head-to-rear accidents decrease when the intersections are under adaptive signal control but increase when surveillance cameras are present. There is also some evidence to suggest that the presence of an uncontrolled left-turn channel, the existence of medians wider than 2 m, higher approach volumes, and more phases per cycle all contribute to higher instances of accidents by both maneuver types.
Methodologies Used to Analyze Collision Experience Associated with Speed Limit Changes on Selected California Highways
Authors: Haselton Curt B. , Gibby A. Reed , Ferrara Thomas C.
Published: April 2007

Three methodologies are used and compared to determine whether there has been a statistically significant change in traffic collisions (total, fatal, fatal plus injury, wet pavement, and nighttime) due to recent speed limit increases on California state highways. The three methods compared were simple regression, analysis of variance (ANOVA), and an observational before–after study developed by Ezra Hauer. Both collision counts and rates were studied for early 1996 speed limit increases from 55 to 65 mph, and from 65 to 70 mph. A comparison group of highways that remained at 55 mph was also studied. The simple regression methodology did not detect nearly as many statistically significant increases as did the ANOVA and Hauer observational before–after methodologies. The latter two methods revealed very similar results, especially for statistically significant increases in total and fatal collision rates and counts. These methodologies also revealed a significant increase in nighttime collisions for the 55–65 mph group. The difference was that the observational method detected only a marginally significant increase with total collisions for the 65–70 mph group. Also, the ANOVA indicated that the fatality collision rate increase for the 65–70 mph group was marginally significant.
Cross-Median Collisions on Pennsylvania Interstates and Expressways
Authors: Donnell Eric T. , Harwood Douglas W. , Bauer Karin M. , Mason John , Pietrucha Martin T.
Published: April 2007

Cross-median collisions (CMCs) on high functional class roadways are a concern because of the potential economic and social losses that often accompany these crashes. The Pennsylvania Department of Transportation (PENNDOT) design policy suggests protecting medians on divided highways where the median width is less than 10m (32.8 ft) and the average daily traffic is above 20,000 vehicles per day. However, CMC crashes have occurred where a barrier was not warranted by the policy. The methodology used to assess median safety on Interstates and expressways in Pennsylvania is reviewed, and the findings are reported. A critical review of literature and an assessment of various state department of transportation median safety practices were undertaken. An expert panel qualitatively assessed median safety practices and provided input for quantitative data collection. Two PENNDOT databases, police accident reports, photologs, and field data were analyzed to complement the qualitative findings. Qualitative results suggest that the three-strand cable system, strong-post W-beam guiderail, or the concrete safety shape are recommended median barriers in appropriate site conditions. Quantitative results show that CMC crashes are rare events; however, nearly 15% involve fatalities and 72% involve nonfatal injuries. In addition, CMC crash rates at earth-divided highways decrease as the median width increases, CMC crashes appear more likely to occur downstream of interchange entrance ramps, and CMC crashes are more likely to involve adverse pavement surface conditions (wet or icy) than are other crashes. Negative binomial regression models were used to model CMC crash frequencies on earth-divided highways.