Using Probe-Measured Travel Times to Detect Major Freeway Incidents in Houston, Texas

Abstract

As a prelude to installing an automatic vehicle identification system for collecting traffic and travel time information from probe vehicles, the Texas Transportation Institute, in conjunction with the Texas Department of Transportation, initiated a pilot study to test the feasibility of using probe-provided travel time information to detect freeway incidents. As part of this pilot study, 200 commuters equipped with cellular telephones were used to collect travel time and incident information from three facilities [I-45 (both the main lanes and the high-occupancy-vehicle lane), the Hardy Toll Road, and US-59] on the north side of Houston, Texas. Historical travel time patterns were developed for each link using data from known incident-free conditions. The statistical principle of standard normal deviates was applied to 11 months of data to determine when a probe travel time exceeded the expected travel time under incident-free conditions. Whereas this approach resulted in detection rates that were lower and false alarm rates that were higher than those reportedly produced by other incident detection algorithms, this study illustrated that some level of incident detection could be achieved using travel time information provided by probe vehicles. Because of limitations in the data, it was not possible to determine the number of incidents that were not detected by the system or the detection times for the known incident conditions.