Alan J. Horowitz

Using Global Positioning System data to understand variations in path choice

A comprehensive set of Global Positioning System (GPS) vehicle location data from Lexington, Kentucky, households was analyzed to determine if such data can be helpful in improving path choice assumptions in traffic assignment models. The portion of the data used consisted primarily of a reconstruction of the street network and the lists of street segments in each path. Analysis was based on matches of trips (e.g., pairs of trips with similar origins and destinations). Matches were obtained for trips within households and for trips across households. Statistics used to compare trips in matches were a path deviation index and the percentage of identical links. It was found that the path chosen on a trip was quite sensitive to the location of the origin and destination and that the chosen path most often differed considerably from the shortest time path across the network. Paths for trips made by the same driver were very consistent over time; paths by different drivers showed more deviations even when the trip ends were the same or very similar. As a result of this research, recommendations are made as to how GPS data on path choice can be better collected in the future for improvement of traffic assignment models.

OPTIMAL ROUTING OF HAZARDOUS MATERIALS CONSIDERING RISK OF SPILL

The diffusion of gases over wide areas from possible spills during transport of hazardous materials is considered when determining the least risk path through a network. Spills could occur through improper operation of vehicle or container or through a collision. Relationships for minimum risk paths are developed for these cases: specific wind directions, uniform average wind direction, maximum concentration wind directions, wind-rose averaged wind directions and speeds, and multiday routing with uncertain weather conditions. The relationships are illustrated for a full-sized urban network. This paper illustrates, how a Geographical Information System approach coupled with elementary principles of optimization theory can be used to solve such complex routing problems. The mathematics developed also reveals some consistent properties of all routing problems that are generalizable. For short trips the least risk path is invariant with the assumed wind speed, the size of spill, and the toxicity of the material. It is also invariant with the selection between uniform average wind direction and maximum risk direction criteria. A hybrid between numerical and analytical methods was adopted to reduce computation requirements which are still large but acceptable.

Forecasting Statewide Freight Toolkit

Federal planning legislation and regulations now mandate that state departments of transportation and metropolitan planning organizations consider the needs of freight when planning and programming transportation investments. While there are standard techniques used to forecast the movement of people, less attention has been paid to forecasting freight movements, and there are consequently fewer standardized techniques that state and local agencies can adapt to their local situation. This Toolkit is designed to provide transportation planners with the information they need to prepare forecasts of freight transportation by highlighting techniques successfully developed by state agencies across the country.

Diversion from a rural work zone with traffic-responsive variable message signage system

An experiment was made to determine the degree of alternative-route selection from a rural freeway that occurs because of implementation of a traffic-responsive variable message signage system in a work zone. The message signs gave real-time estimates of travel time to the end of the work zone. Alternative-route selection was measured through extensive volume counts on the freeway and on parallel arterial streets, both before and after implementation of the signage system. In addition, traffic volumes were measured at a variety of locations where alternativeroute selection was likely to occur and where it was unlikely to occur. Analysis of peak period data found that alternative-route selection rates were between 7% and 10% of the freeway traffic, depending on the location and the day of the week.

SUBJECTIVE VALUE OF TIME IN BUS TRANSIT TRAVEL

A psychological scaling technique, magnitude estimation, is used to rate time spent on various elements of bus transit trips. Relative values of time are found for in-vehicle portions of trips, walking, waiting and transferring. Because magnitude estimation produces a ratio scale, results can be directly incorporated into modal choice analyses, route planning and evaluation procedures where monetary values of time are not necessarily required.

The subjective value of the time spent in travel

Abstract Value of the time spent in travel is a surrogate measure of the comfort, convenience, and reliability of the travel experience as a function of travel model, purpose, and time period and the environmental conditions affecting the trip. Value of time spent in travel is consequently an important element in spatial interaction and transportation analysis. Subjective value of the time spent in travel was measured using a psychological scaling technique, magnitude estimation. Data were obtained from 84 Chicago residents. Completion of the questionaire required each participant to provide judgements of the relative value on 115 different trips in comparison to one standard trip (e.g. a 20 min work trip by automobile). Information gained in this way illustrates the variability that can occur in values of time due to various trip characteristics.

Methodologies for Estimating Vehicle Queue Length at Metered On-Ramps

The ability to monitor vehicle queue length accurately at metered on-ramps can improve ramp meter performance and help to create improved ramp metering algorithms. The queue length distribution can be considered as a continuous analog signal, which consists of both deterministic and stochastic components. Three types of methods for the estimation of on-ramp queue length are discussed: Kalman filter, linear occupancy, and Highway Capacity Manual (HCM) back of queue. Queue data estimated with these methods are compared with field-observed queue data and random number samples. The comparisons indicate that the Kalman filter and linear occupancy methods are usable for real-world operations, but both of them have limitations. The HCM back-of-queue method does not produce reliable estimates for on-ramp queue length.

STATEWIDE TRAVEL FORECASTING PRACTICE: A CRITICAL REVIEW

Many states are now in the process of creating or upgrading their statewide travel forecasting methods. To assist those states, a review of existing forecasting practice was undertaken. This review consisted of interviews and documents from 45 states and of articles from the literature. Passenger models, freight models, and time-series models were reviewed. In addition, statewide models were compared to the many intercity models that were described in academic literature. Little consensus was found as to what should constitute a statewide model, and states varied greatly in their approaches. Those states with complete models tended to follow an urban modeling framework and used software originally designed for urban travel forecasting, in spite of the inherent differences in scales, planning needs, and data availability. Recommendations are made on how states can improve their forecasting methods and tailor them better to statewide planning requirements.

Intersection Delay in Regionwide Traffic Assignment: Implications of 1994 Update of the Highway Capacity Manual

The original 1985 Highway Capacity Manual (HCM85) described widely recognized relationships for traffic delay that could be incorporated into travel forecasts. Applications of the HCM85 procedures demonstrated that such delay relationships were both technically feasible and beneficial. In early 1995, the Transportation Research Board released the 1994 update to the HCM (HCM94), heavily revising the signalized and two-way stop intersection procedures and introducing a detailed all-way stop intersection procedure. These new procedures have the potential to improve the accuracy of forecasts and to make forecasts consistent with other design practices. Implementation of the HCM94 procedures into travel forecasts reveals that fewer adjustments are required to make them work within equilibrium traffic assignments. The two-way stop procedure can be used nearly intact. The signalized intersection procedure, although still requiring some adjustments, allows a greater range of traffic conditions and phasing options. The all-way stop procedure cannot be incorporated into travel forecasts because of its restrictions on allowable volumes and turning movements. Tests of the HCM94 procedures in traffic assignments indicate that they produce noticeably different results (both volumes and link delays) than the original HCM85 procedures. Multiple equilibrium solutions are possible, but the differences between these solutions are small and manageable.

TRANSFER PENALTIES: ANOTHER LOOK AT TRANSIT RIDERS' RELUCTANCE TO TRANSFER

Two on-board surveys were conducted to determine how transit riders perceive transfers. The surveys were conducted before and after the imposition of a transfer in the middle of an existing bus route. Results of the surveys showed that riders perceive bus transit trips as significantly worse when the trip requires a transfer, even if transfer time is neglibible.