The selection of routes in a network along which to transport hazardous materials is explored, taking into consideration several key factors pertaining to the length of time of the transport and the risk of population exposure in the event of an incident. That travel time and risk measures are not constant over time and at best can be known with uncertainty is explicitly recognized in the routing decisions. Existing approaches typically assume static conditions, possibly resulting in inefficient route selection and unnecessary risk exposure. Several procedures for determining superior paths for the transport of hazardous materials in stochastic, time-varying networks are presented. These procedures and their extensions are illustrated systematically for an example application using the Texas highway network. The application illustrates the tradeoffs between the information obtained in the solution and computational efficiency, and highlights the benefits of incorporating these procedures in a decision-sup...

Optimal routing of hazardous materials in stochastic, time-varying transportation networks

The effects of real-time traffic information, supplied at the origin of the trip or along the way (en route), on the system's performance under alternative behavioral rules governing path selection in the network are examined in this paper. Simulation experiments are performed to investigate the effect on overall system performance as well as the incidence of benefits (costs) across user information groups of four experimental factors: (a) behavioral rules, governing users' response to real-time information, (b) sources of information, consisting of point-of-departure or in-vehicle (or both), (c) prevailing "initial conditions" in the system, and (d) market penetration (i.e., the fraction of users with access to real-time information in the network). The results of these simulation experiments provide insights into the effectiveness of real-time advanced driver information systems on systemwide performance and on its critical determinants. The results confirm a priori expectations that the existence of benefits as well as the relative effectiveness of origin-based versus en route information is highly dependent on the initial conditions prevailing in the system as well as the behavioral rules governing path selection. Extreme behavior by users (with frequent switching in myopic response to any gain, no matter how small) could lead to severe worsening of traffic conditions under real-time information from either source. On the other hand, switching according to a boundedly rational model incorporating a threshold improvement in trip time is more likely to lead to meaningful systemwide benefits.

Comparative assessment of origin-based and en route real-time information under alternative user behavior rules

Numerical experiments are performed to test the applicability of the diagonalization algorithm to problems involving asymmetric interactions between passenger cars and trucks in highway networks. Three test networks are considered, including a representation of the Texas highway network, thus providing a realistic case application. The main aspects of the algorithm's performance addressed in these experiments are its convergence characteristics as well as the effectiveness of some computational streamlining strategies. Although convergence is not guaranteed a priori , it was actually achieved in all test cases. Furthermore, it was shown that shortcut strategies can considerably reduce the algorithm's computational requirements. These strategies involve performing only a few “internal” Frank-Wolfe iterations in solving the sequence of diagonalized subproblems. The results suggest the use of less than four internal iterations, with the use of two such iterations exhibiting the highest frequency of best performance in the tests conducted, followed by one and three internal iterations, respectively.

Some numerical results on the diagonalization algorithm for network assignment with asymmetric interactions between cars and trucks

Foreword The ability to model vehicular flows in traffic networks under real-time information, and to provide system users with route guidance information, constitute essential methodological components required to support the successful operation of Advanced Traveler Information Systems and Advanced Traffic Management Systems. This report describes the methodologies and procedures developed through a contract to the University of Texas at Austin, in collaboration with the University of Maryland, to address these essential needs. Specifically, a simulation-assignment methodology has been developed to describe user's path choices in the network in response to real-time information, and the resulting flow patterns that propagate through the network, yielding information about overall quality of service and effectiveness, as well as localized information pointing to problem spots and opportunities for improvement. This methodology is intended for use off-line for evaluation purposes, or on-line for prediction purpose in support of advanced traffic management functions. In additional, algorithmic procedures have been developed to determine the best paths to which users should be directed so as to optimize overall system performance. Powerful extensions to incorporate multiple user classes are also described as well as strategies for real-time operational implementation. Taken collectively, and individually, the procedures described in this report constitute a significant advancement in the state of the art of traffic modelling and dynamic network analysis, and an important step towards the realization of intelligent vehicle-highway systems. Notice This document is disseminated under the sponsorship of the Department of Transportation in the interest of information exchange. The United States Government assumes no liability for its contents or use thereof. The contents of this report reflect the view of the contractor who is responsible for the accuracy of the data presented herein. The contents do not necessarily reflect the official policy of the Department of Transportation. The United States Government does not endorse products or manufacturers. Trade or manufactures' names appear herein only because they are considered essential to the object of this document. escribes the dynamic assignment and traffic simulation models developed to support the functional operating core of ATIS (Advanced Traveler Information Systems) and ATMS (Advanced Traffic Management Systems). Two principal functions are addressed by the assignment simulation models in this context. The first consists of determining, in real-time, the network paths to which the drivers should be directed in going toward their destination, so as to achieve system-level objectives. The second is the prediction or description of the …

Development and testing of dynamic traffic assignment and simulation procedures for atis/atms applications

A Review of Dynamic Assignment and Traffic Stimulation Models for ATIS/ATMS Applications

This report presents an analysis of the effects of highway bypasses on the business activities of a sample of small Texas cities. An initial explanatory analysis (using a before-and-after method, matched pairs, and projected development) did not reveal a significant relationship between highway bypass construction and a change in business volumes. It can be concluded that business volumes in the more rapidly growing cities with imperfect infrastructure and relatively high local traffic benefit from highway bypass construction. On the other hand, initial econometric modeling demonstrated that a highway bypass can have a statistically significant negative effect on business volumes in the small Texas cities that were studied. The results of the econometric modeling show that the way in which a business community responds to a highway bypass is complex. The major factor determining business volumes is the city's population.

Economic effects of highway bypasses on business activities in small cities. interim report

Special truck lanes have been proposed as a measure for dealing with the increasing traffic of larger and heavier trucks on the Texas highway system. This report describes an integrated network modelling methodology for the study of truck lane needs in the Texas highway network. It consists of three major components: critical link programming, network traffic assignment, and optimal link selection/network design. The critical link programs allow the user to diagnose and assess the adequacy of the links in a highway network for handling excessive truck traffic under specified conditions. The traffic assignment model is essential for the prediction of link flow patterns and subsequent user costs calculation in response to particular changes in the network corresponding to truck-related link improvements. The assignment problem addressed here allows the asymmetric interaction between cars and trucks sharing the roadway in the determination of link travel times. The optimal link improvement selection problem is cast as a discrete network design problem with multiple improvement options per link. One of its main features is the definition of link improvement in terms of both lane addition (capacity expansion) and operating scheme (lane access restrictions to cars and trucks).

A Methodology for the Assessment of Truck Lane Needs in the Texas Highway Network

This study analyzed the effects of highway bypass construction on small cities. As this report makes clear, a bypass changes activity patterns within a city, with traffic shifting away from the bypassed route. Increased traffic activity is found on the shortest connector from the bypass to the city center, resulting in increased development along this route. The classification of bypassed cities, one of the key objectives of this study, was developed through cluster analysis. The results of the study suggest that a bypass does not significantly alter the essential characteristics of a city; however, the bypass does have a slightly negative effect on retail sales volumes of the bypassed city.

Traffic and spatial impacts and the classification of small highway-bypassed cities. interim report

Fare policies and pncmg strategies in public transportation systems have important implications on ridership and revenue generation, as well as on the public's perception of the system's equity and cost effectiveness. This study presents a framework for the identification, analysis and evaluation of alternative pricing strategies and fare-related policies, and its application to the Capital Metropolitan Transportation Authority system in the Austin, Texas area. A taxonomy of available fare differentiation schemes is presented, along with a summary of experience with selected schemes in North American transit systems. An extensive review of fare elasticities reported in the literature is presented, with special focus on those associated with free fare experiments. Also discussed are available values for the elasticity of demand for service attributes. A range of elasticities is thus developed for use in the analysis of alternative fare strategies. Several scenarios are analyzed for the Capital Metro system and estimates are developed for the range of ridership and revenue impacts. It is found that, in general, service-related improvements are likely to be more effective than fare reduction or elimination in attracting ridership. Targeted (to particular socioeconomic groups or geographic areas) fare reduction or elimination programs are generally more cost-effective than across-the-board fare cuts. Based on the experience of other localities and on the analysis presented in the report, it does not appear desirable to totally eliminate fares in the Capital Metro system; a possible exception would be as a promotional measure in connection with major service restructuring. Operational and fare payment aspects of the Capital Metro/University of Texas Shuttle system merger are identified, and proposed strategies are analyzed. In particular, two fare policies are considered for possible implementation in the overlapping service areas. The first is a no-fare policy, which is relatively simple to implement, but suffers from possible overcrowding, perceived inconsistency and inequity, as well as additional cost due to lost revenue and increased service requirements. The second policy is an honor system with pre-payment, which has the advantages of perceived consistency and equity, the ability to control abuse, and the contribution to stimulating transaction-free riding through pre-payment systemwide. The primary drawback is the initial effort required for implementation. In addition, fare structures and eligibility requirements for the Special Transit Services (STS) are addressed, in light of information obtained from a survey of several providers. The results of this survey indicate that the Capital Metro fare policy and eligibility requirements are consistent with the other transit agencies.

C M Walton

Papers

Economic effects of highway bypasses on business activities in small cities. interim report

A Methodology for the Assessment of Truck Lane Needs in the Texas Highway Network

Traffic and spatial impacts and the classification of small highway-bypassed cities. interim report

Fare Policies and Pricing Strategies For the Capital Metro Transit System

Traffic and spatial impacts and the classification of small highway-bypassed cities