bluuebunny/crossref_metadata_2025 huggingface dataset:
Benefits of Information Integration in Budget Planning for Pavement Management
Authors: Chan W. T. , Fwa T. F. , Tan J. Y.
Published: April 2007

The budget-allocation process in pavement management occurs at several levels of decision making. In normal practice, the central level is concerned with the allocation of the budget to regional agencies to improve the health of the overall road network, while the regions are responsible for the programming and scheduling of road maintenance in their respective networks. The information processed at different management levels differs, and information at one level may not be readily available to the other. As a result, the maintenance funds allocated by central management to regional highway agencies may not be best used. A budgetallocation procedure based on artificial-intelligence agents is presented; it takes into account information integration between the central and regional management levels by using multiagent systems. Agents are used to facilitate the interaction between decision makers at the two management levels and thus provide a means for vertical information integration. A hypothetical problem containing a two-level funds-allocation structure consisting of a central-level management and three regional highway agencies is investigated. Each regional agency has different road network profiles with different local-level objectives. A genetic algorithm is used as the optimization tool in the decision-making process carried out by each agent. The results are compared with conventional allocation approaches and a two-stage optimization approach. It is shown that, with better integration of information at the different management levels, the resulting budget-allocation strategy produces greater maintenance-cost savings for a given target level of pavement performance.
Multiyear Pavement-Rehabilitation Planning Enabled by Geographic Information System: Network Analyses Linked to Projects
Authors: Tsai Yichang (James) , Gao Bo , Lai James
Published: April 2007

A pavement-rehabilitation planning system enabled by a geographical information system (GIS) is described; it can perform multiyear projectlinked network pavement-rehabilitation analyses subject to funding availability, minimum performance requirements, and other constraints. The system first uses information on the current and historical project-level pavement-condition evaluation stored in the central database to forecast project performance ratings and distresses. It then determines appropriate rehabilitation methods and costs and, finally, calculates life-cycle costeffectiveness ratios for all projects in the pavement network. With this information, the program performs analyses to determine multiyear minimum funding required to meet prescribed pavement-performance requirements and constraints and to determine optimum pavementrehabilitation plans subject to funding availability and other requirements, such as balancing funding distribution or future pavement performance among state congressional districts or Georgia Department of Transportation (GDOT) districts. The system uses dynamic segmentation to create GIS maps, links them with the central database and network analysis results, and thus allows users to make changes to the rehabilitation plans directly on the GIS maps and have the changes reflected automatically in the database. Several examples using the actual data on historical pavement condition evaluations from GDOT are presented to illustrate the capabilities of the system.
Pavement-Distress Data Collection System Based on Mobile Geographic Information System
Authors: Huang Bo , Fwa Tien Fang , Chan Weng Tat
Published: April 2007

In recent years, the development of geographical information systems (GIS) has shifted significantly from desktop applications to mobile field applications. Integrating the precision location data collection capability of a Global Positioning System (GPS) and the spatial processing power of mobile GIS provides an adequate system for field workers to collect data with increased efficiency and ease. This research aims to design and implement a pavement-distress data collection prototype for inspecting airport pavement condition, with the aid of mobile GIS. Unlike the traditional paper forms, the data collection system seeks to offer a customized user interface for distress data entry and a spatial query service. Initial preparation of the airport map layers was carried out on desktop computer using a variety of off-the-shelf software. The required files were then transferred to the personal digital assistant (PDA) for field trials. Two other handheld devices, namely the GPS receiver and digital camera, are attached to the PDA to capture precise location coordinates and digital photos, respectively, of the identified distress. The users are also able to obtain comprehensive search results of the distresses, in both an attribute table and map visualization form. To increase the search efficiency, an indexing method was implemented for the data collected. Trial experimental results show that the applied indexing method has significantly improved the search efficiency over the conventional exhaustive search method.
Dynamic Actions on Bridge Slabs due to Heavy Vehicle Impact on Roadside Barriers
Authors: Bonin Guido , Ranzo Alessandro
Published: April 2007

The use of roadside safety barriers in Italy has changed in recent years: the number of installed devices has increased, and so have their stiffness and resistance. These changes were necessary because early barrier design was inadequate to contain and redirect heavy vehicles. The change in barrier design led to an increase in stiffness and resistance; consequently, the action transferred to the structure by the device increased. The need for resistance on the bridge slabs can be too high because the peculiar action of the roadside barriers was not adequately taken into account in the oldest bridge design codes. In addition, characterizing the actions transferred to the bridge slab is difficult because of the dynamic nature of vehicle impacts on roadside barriers. Given the impossibility of performing a full-scale laboratory test for every bridge deck, the use of computational mechanics applied to dynamic impact/interaction problems is one of the best ways to establish these actions in the project phase. Research was conducted into the use of a three-dimensional finite element model of the bridge slab-barrier-vehicle system to perform a numerical simulation of the impact, according to the procedure used for the roadside barrier homologation crash test, described in the European Standard EN 1317.
Evaluation of Storm Water Catch Basin Inserts for Transportation Facilities
Authors: Edwards Findlay G. , Morgan Robert A. , Brye Kristofor R. , Burian Steven J.
Published: April 2007

Transportation facilities such as parking lots and maintenance yards often do not have provisions to treat storm water before discharge. Catch basin inserts can provide a retrofit alternative as a method to meet the new National Pollution Discharge Elimination System Phase II storm water pollution prevention regulations. Inserts produced by four manufacturers were evaluated for removal of suspended solids and petroleum hydrocarbons by using a pilot scale catch basin and synthetic storm water. In addition, the inserts were placed at operating transportation facilities and monitored for operational problems. At a flow rate of approximately 0.013 m3/s (200 gal/min) and pollutant concentrations for total suspended solids (TSS) and total petroleum hydrocarbons (TPH) of 225 mg/L and 31 mg/L, respectively, the inserts were capable of removing 11% to 42% of TSS and 10% to 19% of TPH.
Laboratory Performance Testing of Open-Graded Friction Course Mixtures
Authors: Watson Donald E. , Cooley L. Allen , Ann Moore Kathryn , Williams Kevin
Published: April 2007

Several lab tests were used in this study to evaluate mixture properties. A draindown test, Cantabro stone loss test, a permeability test, and a modified version of AASHTO T-283 were used to evaluate laboratory performance of open-graded friction course (OGFC) mixes. Some of the more pertinent conclusions were as follows. The CoreLok procedure appears to be a more accurate method of determining bulk specific gravity of compacted specimens than the dimensional method. The minimum air voids content for new-generation OGFC mixtures should be 18% on the basis of the dimensional method and 16% on the basis of the CoreLok method. The addition of fiber stabilizers significantly reduced the potential for draindown. Superpaver; gyratory compactor (SGC)-compacted samples can be used for the Cantabro stone loss procedure. Unconditioned SGC samples should have stone loss of no more than 20%. If an aging process is used, the maximum amount of stone loss should be limited to 24%. Because there is not a significant difference between unaged and aged sample results, the aging procedure is not necessary. Results from this study show no significant difference in tensile strength when one, three, and five freeze-thaw cycles are used in the moisture-conditioning procedure. Therefore, only one freeze-thaw cycle is needed.
Model for Predicting Damage Evolution in Heterogeneous Viscoelastic Asphaltic Mixtures
Authors: de Souza Flávio Vasconcelos , Soares Jorge Barbosa , Allen David H. , Evangelista Francisco
Published: April 2007

Cracking in the asphaltic layer of pavements has been shown to be a major source of distress in roadways. Previous studies in asphaltic mixture cracking typically have not considered the material heterogeneity. The sequel of a study in which the binder and the aggregates were treated as distinct materials is presented. Besides consideration of the viscoelastic behavior of the bulk asphalt binder, a micromechanical viscoelastic cohesive zone model introducing ductility at the crack tip has been considered. The simulations performed are verified and calibrated from simple and conventional laboratory tests. The study investigates crack evolution under monotonic loading, even though the method outlined can be further developed for the investigation of asphalt mixture fatigue.
Cost and Performance Comparison of U.S. Overhead Sign Support Structures
Authors: Ahlborn Theresa M. , van de Lindt John W. , Uzcategui Alonso J. , Lewis Matthew E.
Published: April 2007

Recent developments in fatigue analysis and design of overhead sign support structures prompted AASHTO to update the Standard Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Signals in 2001. An earlier version of the specification was published in 1994 and, according to recent studies, did not adequately address the issue of fatigue. Updating existing sign support structures to comply with the AASHTO 2001 sign specification may result in a substantial expense to the state departments of transportation nationwide. A method was developed to analyze and evaluate overhead sign support structures for comparison based on cost and performance. The method was then applied to sign support structures across the United States to determine the best performing and most economical designs currently in use. To determine the estimated fatigue life of critical connection details, the evaluation of overhead sign support structure performance was based on dynamic analyses of finite element analysis models. Cost evaluation was based on structure weight and its relative constructability. Performance and cost metrics were combined to establish an optimization parameter, providing a quantitative measure of comparison between overhead sign support structure designs. It is therefore a representation of both effectiveness and economy and, because the performance measure is based on fatigue, it is consistent with current trends in overhead sign support structure design. The method may be used by all state departments of transportation and for all different types of sign support structures.
Influence of Cutout Geometry on Stresses at Welded Rib-to-Diaphragm Connections in Steel Orthotropic Bridge Decks
Authors: Connor Robert J.
Published: April 2007

The geometry of the cutout at the intersection of longitudinal ribs and transverse diaphragm plates in steel orthotropic bridge decks can have a significant impact on the stress in the region of the welded rib-to-diaphragm connections. Many different approaches to detailing this connection have been tried, with mixed success. To provide additional guidance to designers, a finite element parametric study that systematically investigated the effect of altering the geometry of certain variables was performed. Parameters considered included overall cutout shape, cutout depth, diaphragm plate thickness, and deck plate thickness. Results indicate that the suggested cutout geometry shown in the current (2002) AASHTO LRFD Bridge Design Specifications for closed-rib orthotropic bridge decks produces increased stresses on this fatigue-sensitive connection. An improved geometry is proposed to replace that currently presented in the specification. Results of this study indicate that larger cutout geometries offer less resistance to out-of-plane displacements induced by longitudinal rib rotations. As a result, out-of-plane stresses are decreased at the connection. However, cutouts that are excessively deep will increase in-plane stresses at the welded rib-to-diaphragm connection. If the cutout is too shallow, out-of-plane stresses may become prohibitively high owing to restraint of longitudinal rib rotations. Cutouts that are between 1/3 and 1/2 the depth of the rib with transition radii at the top of the cutout of 50 to 75 mm and vertical cuts are most favorable. The cutout geometry shown in the AASHTO LRFD specification results in an overstiff cutout detail. A proposed improved geometry is presented.
Field Measurements of Old Brick Culvert Slip Lined with Corrugated Steel Culvert
Authors: Vaslestad Jan , Madaj Arkadiusz , Janusz Leszek , Bednarek Barbara
Published: April 2007

Thousands of culverts in the highway and railway system are in various states of deterioration, ranging from minor serviceability problems to serious functional and safety problems. One of the most effective ways to restore an old culvert to a functional condition is slip lining, the process of lining an old culvert with a new prefabricated one. Field measurements carried out on a 100-year-old brick culvert in Poland slip lined with a corrugated steel plate culvert (CSPS) are described. The new steel culvert is a pipe arch with a span of 4.26 m and height of 2.95 m. The steel culvert was assembled inside the old brick culvert without stopping traffic on the road. The space between the old culvert and the new steel culvert was filled with concrete with a compressive strength of 15 MPa. The old brick culvert was instrumented to measure strains under test load. The new steel culvert was instrumented to measure strains during the backfilling and test load. Earth pressure cells were installed in the foundation below the steel culvert to measure the pressure of the CSPS onto the subsoil. A truck with a total weight of 321 kN was used for the test load. The measured strains during test load were recorded when the truck was placed at various locations. Measurements show interaction between the old and new culvert. The redistribution of stresses that can indicate strengthening of the brick culvert was observed. Long-term measurements were taken 1 year (2001) and about 3 years (2003) after the slip lining was installed. The structure was also analyzed with the finite element method (FEM). The stress distribution obtained from the 2003 test is similar to the distribution obtained from the finite element method.
Concrete Maturity Field Studies for Highway Applications
Authors: Tepke David G. , Tikalsky Paul J. , Scheetz Barry E.
Published: April 2007

The Arrhenius maturity function was used to estimate strength evolution in three highway structures: a bridge pier, a bridge deck, and pavement. The research documents field instrumentation and strength estimation. Each structure was constructed with a mixture containing 35% ground granulated blast-furnace slag as a mass replacement of total cementitious materials and approximately a 0.40 water-cementitious materials ratio. The temperature profiles for each application were recorded and discussed. The logarithmic strength-maturity relationship was compared with the hyperbolic strength-maturity relationship for each application. Cylindrical concrete specimens, cast on site during construction, were exposed to a variety of curing conditions. Minor differences in material proportions were also investigated. The quality of cure of the companion specimens significantly affected the strength-maturity relationship. Small deviations in mixture proportions did not appear to affect significantly the strength maturity relationship for the mixtures studied.
Air-Void Characteristics of Concretes in Different Applications
Authors: Ozyildirim Celik
Published: April 2007

Concrete that can be critically saturated and exposed to cycles of freezing and thawing must be properly air entrained for long-lasting service. Otherwise, cracking occurs, with the resultant deterioration of the concrete. Air voids must be small in size, closely spaced, and uniformly distributed to ensure adequate resistance to freezing and thawing as well as satisfactory strength. An increase in air volume results in a reduction in strength. Air content is affected by material properties, including water and admixture content, and construction practices, including pumping and consolidation. The air entrainment and air-void system in concretes that have a stiff consistency, are pumped, or have a large amount of high-range water-reducing admixture are addressed. Under those conditions an improper air-void system may result and may have an adverse effect on the concrete's resistance to freezing and thawing. Thus, the air-void system must be evaluated and necessary precautions taken. Precautions taken by the Virginia Department of Transportation are summarized.
Numerical Analysis of Effect of Sampling of Alternatives in Discrete Choice Models
Authors: Nerella Sriharsha , Bhat Chandra R.
Published: April 2007

A multitude of alternatives characterize the choice set in many activity and travel choice contexts. Analysts generally sample alternatives from the choice set in such situations because estimating models from the full choice set can be very expensive or even prohibitive. Numerical experiments were undertaken to examine the effect of the sample size of alternatives on model performance for both a multinomial logit model (for which consistency with a subset of alternatives is guaranteed) and a mixed multinomial logit model (for which no consistency result holds).
Hybrid Discrete Choice Departure-Time and Duration Model for Scheduling Travel Tours
Authors: Vovsha Peter , Bradley Mark
Published: April 2007

A new model for scheduling travel tours is described. The model is essentially a discrete choice construct that operates with tour departure-from-home and arrival-back-home time combinations as alternatives. The proposed utility structure, based on continuous-shift variables, represents an analytical hybrid that combines the advantages of a discrete choice structure (flexible and easy to estimate and apply) with advantages of a duration model (parsimonious structure with a few parameters that support any level of temporal resolution including continuous time). The hybrid model currently has a temporal resolution of 1 h, which is expressed in 190 hour-by-hour departure- and arrival-time alternatives. The model is applied sequentially for all tours in the individual daily activity-travel pattern according to a predetermined priority of each activity type. The enhanced temporal resolution allows for applying direct availability rules for each subsequently scheduled tour to be placed in the residual time window left after the tours of higher priority are scheduled. This feature ensures a full consistency for the whole individual daily schedule. The model has been estimated and applied as a part of the new regional travel demand model developed recently for the Mid-Ohio Regional Planning Commission.
Relationship of Shopping Activity Duration and Travel Time with Planning-Level Network and Socioeconomic Factors
Authors: Rosen David , Shankar Venkataraman N. , Ulfarsson Gudmundur F.
Published: April 2007

The journey to work has been extensively studied. The majority of travel, however, takes place outside that context. The concept of time use as applied to travel behavior has developed with the understanding that travel occurs in relation to the spatial separation of activities and according to the needs and constraints imposed on travelers by their time schedules, sociodemographic characteristics, and network characteristics. The statistical methodology used to elucidate the underlying motivations affecting travel to evening shopping activities, a largely unstudied area of travel behavior, is described. Methods of testing for selectivity bias and endogeneity are also described and applied. Corrective measures are taken and explained, including instrumental variables and system methods of regression. Travel time and activity duration are found to be endogenous and positively correlated. Travel time increases with greater vehicle ownership, duration of preceding work activity, transit use, and duration of free time preceding the trip. Travel time decreases for trips that start later in the evening and later in the week and with increased destination-node density. For teenagers aged 15 to 17, activity duration increases with number of passengers when preceded by longer shopping activities. Activity duration decreases with greater percentages of high-rent housing in the census tract, with household size, with number of workday trips, and for men.
Day-to-Day Evolution of Network Flows Under Route-Choice Dynamics in Commuter Decisions
Authors: Srinivasan Karthik K. , Guo Zhiyong
Published: April 2007

The day-to-day dynamics of commuter decisions on urban traffic networks induced by route-choice dynamics is investigated. More specifically, this investigation analyzes the stability and reliability of system performance due to route-choice dynamics under real-time information, relaxing key restrictions associated with user equilibrium models. A simulation-based framework is developed to analyze day-to-day dynamics by integrating an empirically calibrated model of route-choice decisions with a dynamic network assignment model. Computational experiments are used to investigate the effect of certain experimental factors—recurrent network congestion level, market penetration, nature of information, and frequency of information updates—on network performance stability and reliability. The findings provide evidence of considerable day-to-day variations and stochasticity in network flows and performance, even when departure-time decisions and the origin-destination matrix are assumed to be fixed. The results indicate that (a) network performance may deviate significantly from equilibrium because of route-choice decisions under information; (b) within-day route choices have a significant effect on day-to-day network flow evolution; (c) user equilibrium path flows may not be reached or may not be stable when uncoordinated route-choice decisions are made under real-time information; (d) route-choice decisions do not exhibit convergence to an equilibrium, although the switching rate may be near steady-state conditions; (e) advanced traveler information systems (ATIS) information strategies can affect both within-day and day-to-day dynamics; and (f) some information strategies can lead to improved reliability and stability but at the expense of longer trip times. The results indicate that the trade-off between trip time performance and stability must be considered in network analysis and design. These results have important implications for the design of traffic control strategies, more-effective ATIS implementation guidelines, and incident management strategies.
Travel Time Perception and Learning Mechanisms in Traffic Networks
Authors: Chen Roger , Mahmassani Hani S.
Published: April 2007

Models of travel time perception and learning mechanisms in traffic networks are presented. Mechanisms for updating travel times in light of new experiences and for triggering and terminating the updating process are examined. Travel time perception and learning are modeled on the basis of concepts from Bayesian statistical inference. Mechanisms for triggering and terminating the learning process are modeled with the use of simple heuristic rules based on the inter-update period and thresholds that define the salience of travel times and acceptable confidence levels. These models are embedded inside a microscopic (agent-based) simulation framework and model to study their collective effects on the day-to-day behavior of traffic flows through a series of experiments. The effect of alternative travel time perception and learning mechanisms on system performance and its dynamic properties, in particular convergence, is explored.
Changes in Transport Behavior by Fragmentation of Activities
Authors: Nobis Claudia , Lenz Barbara
Published: April 2007

An empirical study was made with the aim of revealing the relationship and interaction between use of information and communications technology (ICT) and travel behavior. To this end, a concept is developed built around the basic idea that technological developments, both in the travel and especially in the communications sector, increase flexibility and thus enable a fundamental reorganization of activities. A major feature of the interplay between ICT and travel is the spatial-temporal fragmentation of activities, which can cause both quantitative and qualitative changes in traffic volume. Questions about changes in such routine behavior can only be answered by a long-term study. For this reason, the study presented here is set up as a representative panel investigation, allowing further studies in the future. With the results of the first set of data, the relationship is described between communication and mobility patterns and individual characteristics of people with varying affinities to ICT and what activity-specific ICT use is typical for groups of varying affinity. The initial evaluation of an extensive set of data allows a clear description of the relationship among ICT use, communications behavior, and mobility behavior, while providing evidence that such questions are legitimate.
Development of an Empirically Based Area-Type Model
Authors: White Wade , Lamb Daniel R. , Yun Seongsoon
Published: April 2007

Area type is often used in traditional four-step travel demand models as a predictive variable. Most often it is a factor in mode choice, but it is also commonly used in trip generation as well. Yet a reliable, fore-castable, and measurable definition of area type is generally not documented in most travel demand models. In fact, there is little literature on the subject of predicting area type in the context of travel demand models. This can be troublesome when models are applied to long-range forecasts where significant changes in population and employment result in changes in the general character of an area. With Delphi methods, geographic information system analysis, and discriminant analysis, this study documents the development of an empirically based area-type model in the Tampa Bay region. Because in many ways Tampa Bay's urban form is typical of many cities in the United States, the results should be readily transferable to other urban areas.
Bay Area Rapid Transit's San Francisco, California, International Airport Station: Assessment of Transit Patronage and Revenue Forecasts
Authors: West Ron , Herhold Pamela
Published: April 2007

This study examines patronage and revenue forecasts for the newly opened San Francisco International Airport (SFIA) Bay Area Rapid Transit (BART) station in California. As an outgrowth of a September 2002 analysis to determine whether a $1.50 premium surcharge at the SFIA station was sufficient to pay off revenue bonds, this study examines how a series of assumptions about BART services and fares have changed since publication of the final environmental report in 1996. Patronage and service projections are evaluated for three time periods: the 1996 final environmental document, the September 2002 analysis for the purpose of issuing revenue bonds, and an updated 2003 analysis leading up to the start of revenue service. These projections are compared with the first weeks of revenue service that began in June of this year. In general, the 1996 environmental analysis overstated projected ridership and service levels. However, based on updated analyses that took into account realistic service levels, fare increases, parking charges, and a downturn in the regional economy, the most recent projections of ridership are reasonably accurate, and projections of fare revenues are right on target. The study concludes that projected growth in patronage at the SFIA BART station may be quite reasonable, assuming a turnaround in the economy in the near future, and provides a benchmark for establishing more reasonable sets of assumptions to be used in analyzing future Bay Area rail improvement projects.
Development of a Mechanistic-Empirical Structural Design Procedure for Continuously Reinforced Concrete Pavements
Authors: Selezneva Olga , Rao Chetana , Darter Michael I. , Zollinger Dan , Khazanovich Lev
Published: April 2007

The concepts and approach used to develop a mechanistic-empirical structural design procedure for continuously reinforced concrete pavements (CRCP) are presented. Key aspects of the CRCP design procedure— including design overview, design inputs, structural response model, incremental damage analysis, and prediction of CRCP deterioration— are addressed. The mechanism of punch-out development is the foundation of the structural design procedure. Punch-out development is modeled by using mechanistic principles and damage accumulation over the design life. The incremental damage is used to account for changes in many factors throughout the entire design period, including material properties (portland cement concrete strength and modulus, erosion of base), seasonal climatic conditions, traffic loadings, crack load transfer, subgrade support, and others. Each analysis increment represents a specific combination of these factors during a selected period of time. Finally, accumulated damage is correlated with CRCP punchouts by using extensive field data, and a sensitivity analysis is provided to show that the procedure is reasonable.
Simplified Design of Roller-Compacted Concrete Composite Pavement
Authors: Delatte Norbert
Published: April 2007

Roller-compacted concrete (RCC) is a durable, economical paving material for heavy-duty traffic. In the past, most RCC pavements have been built for low-speed traffic because of the difficulty of producing a smooth surface. A composite pavement system consisting of an RCC pavement structure and a hot-mix asphalt (HMA) riding surface is proposed. Simplified design tables, based on mechanistic analysis, are presented. Only fatigue cracking was considered, because performance studies of RCC have shown very little tendency for joint or crack faulting. Use of the design procedure is illustrated through an example. Results are compared with several other design procedures. Guidance for materials selection for the HMA surface layer and the subbase layer is provided, and construction considerations are reviewed. Cost data show that the initial cost of RCC pavements may be as low as 62% of the cost of conventional paving alternatives (not counting the HMA surface course). Suggested areas for further research into RCC composite pavements are discussed. The advances in RCC technology over the past two decades have made RCC a durable, economical alternative for industrial and multimodal pavements. Further use of RCC as part of a composite pavement system for highways offers considerable potential. One obstacle to use of RCC for highways has been the absence of a suitable design procedure. That need has been addressed in this research.
Pavement Responses Due to Hard Landings of Heavy Aircraft
Authors: Kuo Shiou-San , Mahgoub Hesham S. , Holliday Russell D.
Published: April 2007

The effects on airport runways of impact loads induced by hard landings of heavy aircraft have been investigated. A hard landing is defined as a landing in which the angle of landing by a single-wheel impact load is greater than the static load for the same aircraft, with inclusion of the effects of the shock-absorption system. A numerical model, based on some earlier work by others, was developed to define the impact load for any given landing angle. With the impact-load values calculated from the model, theoretical stresses and strains were computed by existing elastic-layer and finite-element computer programs. The results indicated that tensile strains at the base of the asphalt layer and compression strains at the top of the subgrade could be up to 10 times as high under impact loading than under static loading. The study concluded that impact loads caused by angles of landing between 0.2° and 0.8° above horizontal were not greater than the static load of the aircraft (upon which current design standards are based). However, at angles of landing greater than about 0.8°, the fatigue cracking and permanent deformation of airport runway pavements increased exponentially with an increase in landing angle. As a result of this study, the effects of impact loads due to hard landings were demonstrated to be sufficiently significant to be considered in the design of airport runway pavements.
Fatigue Cracking Mechanisms in Asphalt Pavements with Viscoelastic Continuum Damage Finite-Element Program
Authors: Mun Sungho , Guddati Murthy N. , Kim Y. Richard
Published: April 2007

A study of fatigue-cracking mechanisms in asphalt pavements used the finite-element program VECD-FEP++. This program employs the viscoelastic continuum damage model for the asphalt layer and a nonlinear elastic model for unbound layers. Both bottom-up and top-down cracks are investigated by taking several important variables, such as asphalt layer thickness, layer stiffness, pressure distribution under loading, and load level applied on the pavement surface, into account. The cracking mechanisms in various pavement structures under different loading conditions are studied by monitoring a damage contour. Preferred conditions for top-down cracking were identified with the results from this parametric study. The conjoined damage contours in thicker pavements suggest that a through-the-thickness crack may develop as the bottom-up and top-down cracks propagate simultaneously and coalesce; that idea supports observations from field cores and raises the question of the validity of traditional fatigue performance models that account for the growth of the bottom-up cracking only.
Developing Software for Elastic Analysis of Pavement Structure Responses to Vertical and Horizontal Surface Loadings
Authors: Maina James W. , Matsui Kunihito
Published: April 2007

In this research, a pavement is modeled as a multilayered elastic system composed of a subgrade that is assumed to be a semi-infinite medium. On top of the sublayer are layers of finite thickness infinitely extended horizontally. Furthermore, it is assumed that vertical loading, such as wheel load, and horizontal loading, such as brake load, are simultaneously applied at the surface of a road or runaway pavement. This load is assumed to be circular and uniformly distributed over the entire area. Expressing the displacement function of Navier's equation in a cylindrical coordinate system through harmonic and biharmonic functions, the analytical solution method is obtained by using Michell and Boussinesq functions as well as Hankel transformation and Hankel inverse transformation. In this research, a program called GAMES, which can find pavement responses to multiple vertical and shear loadings, was developed. Theoretical analysis uses the principle of superposition, and the solution is given by summing up the solutions from vertical and horizontal loads. The accuracy of this program is confirmed by comparing results for a number of worked examples with results obtained using the BISAR program. It is also possible to allow an interface slip modeled in a form of shear spring. The current version of this program allows for analysis of 10,000 measurement points with a maximum of 100 loads and 100 pavement layers.
Analysis of Pedestrian and Bicycle Casualties with Regional Panel Data
Authors: Noland Robert B. , Quddus Mohammed A.
Published: April 2007

An analysis is presented of pedestrian and bicycle casualties by using cross-sectional time series data for the regions of Great Britain. A fixed-effect negative binomial model is used that accounts for heterogeneity in the data and the distributional properties of count data. Various factors associated with those killed and seriously injured as well as with slight injuries are examined. These include the average age of vehicles in the region, the road length of various road classes, vehicle ownership in the region, per capita income, per capita expenditure on alcohol, age cohorts, and various proxies for medical technology improvements. Various specifications of the models are estimated. Generally, it is found that more serious pedestrian injuries are associated with lower-income areas, increases in percent of local roads, increased per capita expenditure on alcohol, and total population. Statistical effects are more difficult to detect in models with serious injuries for bicyclists, but alcohol expenditure is strongly associated with increased injuries. This work has implications for transport policy aimed at increasing the modal share of pedestrians and bicyclists. Further research is needed to clearly understand some of the trends found in the analysis, especially the effect of changes in medical care and technology on total injuries.
Safety Effects of Narrow Lanes and Shoulder-Use Lanes to Increase Capacity of Urban Freeways
Authors: Bauer Karin M. , Harwood Douglas W. , Hughes Warren E. , Richard Karen R.
Published: April 2007

Congestion on urban freeways often creates a need to increase freeway capacity by adding an additional lane. Although adding a lane by widening the existing roadbed is often difficult and expensive, restriping the traveled way with narrower lanes, converting all or part of the shoulder to a travel lane, or a combination of both often is a practical solution. An observational before-and-after evaluation with the empirical Bayes method was done to examine the safety effects of projects involving narrower lanes or shoulder conversions on existing urban freeways in California with four or five lanes in one direction of travel. The evaluation found that projects converting four lanes to five lanes resulted in increases of 10% to 11% in accident frequency. Projects converting five lanes to six lanes resulted in smaller increases in accident frequency. These increases in accident frequency may be the result of accident migration caused by relocation of traffic operational bottlenecks.
Statistical Road Safety Modeling
Authors: Hauer Ezra
Published: April 2007

The hope is that statistical models fitted to historical data can be used to estimate the effect of road design elements on safety. Whether this can be done is not clear. A sign of trouble is that models based on diverse data sets tend not to yield similar results. Suggestions are made on how to increase the chance of success in this quest. Emphasis is on three questions: Which variables should serve in the model? What mathematical function should represent their influence? How does one check whether the representation of the influence of a variable is appropriate?
Linking Roadway Geometrics and Real-Time Traffic Characteristics to Model Daytime Freeway Crashes: Generalized Estimating Equations for Correlated Data
Authors: Abdel-Aty Mohamed , Abdalla M. Fathy
Published: April 2007

A model was developed to predict daytime crashes on a freeway when real-time traffic flow characteristics and roadway geometric features are known. The data used were for 337 daytime crashes that occurred on Interstate 4 in 1999 in Orlando, Florida (13.25 mi), where corresponding loop detector traffic data were available up stream and downstream of the location of every crash and for at least 30 min before the crash occurred. The traffic data included average speed, volume, and occupancy rate for every 30 s at 0.5-mi intervals. Traffic characteristics for noncrash cases at the same locations and at similar times of the crash cases were extracted and fed to the model. The generalized estimating equations technique with binomial probit link function was used to account for correlation between crashes that occurred at the same location. Three different correlation structures (independent, exchangeable, autoregressive) were used, discussed, and compared. The modeling results showed that the existence of an on-ramp increases the likelihood of a crash within 0.5 mi downstream of the crash location. High variability in speed for a period of 15 min in a certain location was shown to increase the likelihood of a crash 0.5 mi downstream. Unlike speed, low variability in volume over 15 min was shown to increase the likelihood of a crash at 1 mi downstream.
Explicit Consideration of Safety in Transportation Planning and Project Scoping
Authors: Kononov Jake , Allery Bryan K.
Published: April 2007

The Transportation Equity Act for the 21st Century of 1998 required explicit consideration of safety in the transportation planning process. Although this government mandate is well intentioned, little is known about how to accomplish it. Despite 60 years of modern road building, there is still no consensus among transportation professionals about how to quantify the degree of safety or lack of safety of an existing transportation facility. It is even more difficult to anticipate the level of safety on highways not yet built. A methodology for the explicit consideration of safety in the transportation planning process is presented, followed by a review of two case histories illustrating its application.
Intersection Safety at High-Speed Signalized Intersections: Number of Vehicles in Dilemma Zone as Potential Measure
Authors: Zimmerman Karl , Bonneson James A.
Published: April 2007

High-speed signalized intersections may have both safety and operational problems. The safety problems traditionally have been solved with the use of dilemma zone protection of some form. However, dilemma zone protection tends to be associated with an increasing chance of running the phase to its maximum allowable duration—a max-out. At max-out, any provided dilemma zone protection ceases and any number of vehicles may be in the dilemma zone, a situation that creates the safety problem the system was meant to prevent. Most methods for assessing the safety of intersections do not include an assessment of signal operations. Reducing the number of vehicles in the dilemma zone for an intersection approach should reduce the number of drivers who do not receive dilemma zone protection and thereby reduce the probability of crashes for those approaches. A theoretical method calculates the number of vehicles in the dilemma zone at the end of a green phase, which can then be used to compare real-world and theoretical performance of different detection systems. An illustrative example provides one such comparison. Also, a field data collection method is provided for the assessment of a signal system in operation.
Incident Clustering: Diagnostic Approach for Assessing Usability of Intersections and Other Road Sites
Authors: Hanowski Richard J. , Medina Alejandra L. , Wierwille Walter W. , Lee Suzanne E.
Published: April 2007

During the course of an FHWA-sponsored research project, driver errors in crashes and near-crashes (i.e., critical incidents) were investigated, and an analysis approach was developed with which to identify infrastructure-related and non-infrastructure-related problems at intersections and other roadway sites. Referred to as a specific site critical incident analysis, this analysis approach consisted of four general steps: ( a) selection of a site, ( b) careful review of the site's critical-incident data, ( c) determination of the potential critical-incident contributing factors, and ( d) identification of incident clusters. An incident cluster is a group of critical incidents with similar characteristics that occur at the same location. From these incident clusters, researchers gained insight into potential infrastructure-related and non-infrastructure-related causal factors associated with critical incidents and, subsequently, could redesign solutions. An overview is presented of the incident cluster approach, as is an example analysis conducted for the driver error project.
Forecasting Crashes at the Planning Level: Simultaneous Negative Binomial Crash Model Applied in Tucson, Arizona
Authors: Ladrón de Guevara Felipe , Washington Simon P. , Oh Jutaek
Published: April 2007

At least two important transportation planning activities rely on planning-level crash prediction models. One is motivated by the Transportation Equity Act for the 21st Century, which requires departments of transportation and metropolitan planning organizations to consider safety explicitly in the transportation planning process. The second could arise from a need for state agencies to establish incentive programs to reduce injuries and save lives. Both applications require a forecast of safety for a future period. Planning-level crash prediction models for the Tucson, Arizona, metropolitan region are presented to demonstrate the feasibility of such models. Data were separated into fatal, injury, and property-damage crashes. To accommodate overdispersion in the data, negative binomial regression models were applied. To accommodate the simultaneity of fatality and injury crash outcomes, simultaneous estimation of the models was conducted. All models produce crash forecasts at the traffic analysis zone level. Statistically significant ( p-values < 0.05) and theoretically meaningful variables for the fatal crash model included population density, persons 17 years old or younger as a percentage of the total population, and intersection density. Significant variables for the injury and property-damage crash models were population density, number of employees, intersections density, percentage of miles of principal arterial, percentage of miles of minor arterials, and percentage of miles of urban collectors. Among several conclusions it is suggested that planning-level safety models are feasible and may play a role in future planning activities. However, caution must be exercised with such models.