Obtaining near real-time information of travel times is a critical element of most applications of intelligent transportation systems. The use of transit vehicles as probe vehicles for collecting travel time data for automobiles on urban corridors was examined. Because transit vehicles are increasingly equipped with an automated vehicle locator (AVL) for reporting the current location of the vehicle, it may be possible to use the AVL data for travel time purposes. In anticipation of such an application of AVL, the relationship between travel times of a transit vehicle and of an automobile is examined for stability of data and adjustment needs. Travel times of transit vehicles and automobiles were measured simultaneously along the same sections on major corridors in Delaware. The difference in travel times was relatively stable, and, hence, appropriate formulas for predicting the travel time of automobiles were developed. The model coefficients were found to be reasonable and stable for various traffic conditions. The study suggests that the AVL-equipped transit vehicle can be used as a probe vehicle to collect travel time data at regular intervals with minimum cost. Applications of transportation demand management (TDM) and intelligent transportation systems (ITS) have become the central strategy for mitigating congestion in many cities. An important element of such schemes is a system that collects, predicts, and disseminates traffic information to drivers in real time (1, 2). Perhaps the most critical information required by the traveler and managers of ITS is the travel time on the links of the network. The problem, however, is how to collect the data, predict travel time for the immediate future, and disseminate the information continuously. Much research is being conducted into each of these aspects, including the device and mechanism with which to collect and transmit travel times. Figure 1 is a schematic of the state of the art in travel time prediction, and the figure identifies where the topic of this paper fits into the scheme of travel time prediction. This study examines the possibility of using transit vehicles (buses) as probe vehicles for collecting data for predicting automobile travel time. This idea is motivated by the introduction by a large number of transit agencies of the automated vehicle locator (AVL) on their buses. AVL uses a Global Positioning System (GPS) to report the current location of the bus as it travels. The original purpose of AVL was to provide arrival time information to passengers and to report the current location to transit management. However, the information collected by AVL could also become the basis for calculating the travel time of automobiles. As discussed here, the use of buses as an information source has several benefits. Despite the utility of buses as a possible data source on travel time, little or no work has been done to investigate the validity and usability of this source and how to convert the data to predict the average travel time of automobiles. This study determines whether buses can be used as probe vehicles in an urban traffic stream by analyzing the nature of the information collected by the buses and developing formulas to convert the travel time of a bus to that of the automobile. For this study, a large volume of data on bus and automobile travel times was collected and analyzed on various sections of arterials in the northern part of New Castle County, Delaware. The problem analyzed here is to develop a procedure that predicts the average travel time of the automobile, ATT, as based on the observed travel time of a bus, BTT, in the same traffic stream. The procedure should be simple yet accurate. The tasks involved are as follows: • To measure the travel time of the bus and of the automobile for the same section at the same time; • To analyze the characteristics of the components of BTT and their variability; • To develop a model that converts the travel time of the bus to the average travel time of the automobile; and • To verify the model by the data collected. Consider the schematic presentation of the changes in travel time between two points over time shown in Figure 2 . The solid line shows the average travel time of the automobile from Point A to Point B for the corresponding departure time on the x-axis; the line indicates that the vehicle that departs A at time T takes Z minutes to reach B on the average. The purpose of the travel time prediction models, in general, is to predict travel times that are close to this solid line. The figure also shows x, which indicate BTT over the same section for the corresponding departure times on the x-axis. These points are expected to be located above the solid line (which are ATTs).
By examining the relation between travel times of a transit vehicle and of an automobile, REF shows that buses with AVL systems can be used as a probe to collect travel time data at regular intervals cost effectively.
Using Bus Travel Time Data to Estimate Travel Times on Urban Corridors
Transportation Research Record
Engineering