Travel Time Estimation on the San Francisco Bay Area Network Using Cellular Phones as Probes

Problem

Currently, travel time estimates are largely based on data from road sensors embedded in the pavement. These loop detectors wear out and require a certain amount of maintenance and construction costs. This report explores the possibility of gathering travel time information using cellular telephones, which many drivers in the Bay Area already carry in their vehicles.

Method

The FCC E-911 mandate requires that cellular phones be locatable to an accuracy of about 125 meters by October, 2001, which means that cellular positioning systems are very likely to be implemented in most areas of the US within a few years. This paper discusses the basic technological issues in cellular positioning, and developments that are already taking place in this field. We present results from several analytical and simulation models, which provide insight into the various parameters that will affect the performance of positioning systems. We also look at the business issues, and discuss how a field trial could be carried out.

Findings

Cellular positioning technology is a very active area of research, and a number of different solutions are being worked on. The prospects of developing an accurate positioning system within the time frame demanded by the FCC are good.

Accurate travel time estimates will be possible provided around 5% of vehicles on the Bay Area network are equipped with live (i.e. switched-on) cell phones, and evidence suggests that they will be.

Our analysis also suggests that cellular telephone positioning could be a cost-effective method of garnering travel-time estimates. The system load needed to make the measurements is only a small proportion of total capacity, and cellular operators might be interested in implementing travel time estimation as a secondary business operation.

A field test depends on PATH researchers being able to access cell phone positioning technologies, much of which is being undertaken in conditions of industrial secrecy. Data collected using cell phone systems would have to be compared to data obtained from the road network; the stretch of I80 between Albany and Emeryville is well instrumented and can provide fairly accurate travel time information, and can be confirmed using GPS-equipped vehicle probes.