Estimating nationwide link speed distribution using probe position data

The purpose of this study was to investigate different methods of estimating speeds on links in United States' nationwide transportation network from different sources, such as probe vehicles and loop detectors. The Trip Speed Assignment Technique was developed and applied to the probe vehicle data to create speed distributions by time of day for many of the major roadway segments of the U.S. highway system. The technique can generate average speeds for a large network using a relatively small sample size. The average speeds follow general traffic patterns. Thus it is possible to use the probe vehicle data with the Trip Speed Assignment Technique to provide appropriate travel speed information for a large area. Exhaustive spot loop detector data have been used to compare the accuracy of the speeds derived from the Trip Speed Assignment Technique. Discrepancies are discussed and recommendations are made to improve the Trip Speed Assignment Technique.