This project explored the use of commercially available consumer GPS data in travel reliability studies by examining two TomTom traffic data products, namely MultiNet and TrafficStats, which produce respectively time-of-day link travel speed profile and travel time statistics on selected routes. The project had two primary objectives. The first was to evaluate the quality of the aforementioned commercial data products using publically available traffic sensor data (specifically, Gary-Chicago-Milwaukee, or GCM, database) and the second to evaluating the impacts of this new data source on reliable route guidance. The findings from the project case study are as follows:
• TomTom speed profile data generated average travel time estimations for highway segments that matched those from GCM data reasonably well. However, estimated average link travel times from TomTom were about 10% – 15 % lower than those from GCM data.
• Using TomTom data as a benchmark, it was found that the travel times on arterial streets were severely underestimated in the GCM database. Note that these arterial travel times were estimated because no direct observations were available.
• The daily speed profiles obtained from TomTom and GCM data did not match well on most expressways examined in this study. In general, TomTom data tended to underestimate the travel speeds on expressway segments. It appears that, in most cases, TomTom caps the speed at the legal limit, which is not the true free flow speed, as revealed from the GCM data.
• The quality and usefulness of the data provided by TrafficStats raised more concerns. For one thing, the percentile route travel times provided in the route reports seemed to spread out too much and had variances too high to be realistic in most cases. More problematic was the fact that these percentile travel times did not match the reported route segment statistics, especially in terms of variances. Therefore, one needs to consider the utility of this product with cautions, especially given its high price.
• The reliable routing experiments conducted in this project showed that the reliability routing results changed significantly after TomTom data was used to generate travel time distributions on the arterial streets. The main reason for this change was that the travel times on arterial streets in GCM were severely underestimated. As a result, many arterial-based paths that were found reliable for certain risk-taking preferences were no longer attractive because they became much longer when TomTom data was used. This finding suggests that MutliNet speed profile may be used to as a supplementary data source for travel reliability studies.
The project generated a new TomTom database that stores all TomTom data acquired in this project, as well as a GCM database. Both databases are managed using PostgreSQL system on a server hosted at Northwestern University. The project also developed an application, called RIDEA (or Reliability-IDEA) based on the VNET platform. VNET is a simple, flexible and extensible graphic user interface that supports a wide variety of network-related applications. RIDEA is available for download, along with the VNET platform, at https://translab.civil.northwestern.edu/nutrend/?page_id=53. RIDEA provides a graphical interface to access and visualize the databases and to conduct reliable routing experiments. It may be used as a prototype to support future commercial software development for travel reliability analysis.
The contractor's final report is available.
