ABSTRACT
The use of GPS-equipped smartphones by drivers can facilitate the tracking and monitoring of vehicle operations in real-time. This kind of solution would be implemented to obtain estimates of individual vehicle operating speeds from the traffic stream. However, before GPS data can be used in safety performance analysis, tracking errors caused by en-route satellite signal disruptions need to be taken into account to accurately reflect real-world traffic conditions. The main aim of this paper is to demonstrate how, when adjusted for errors, GPS-based estimates of instantaneous speeds can be used to highlight locations where safety is compromised due to poor road geometry. A vehicle-specific Track Safety Performance Index (TSPI) is developed to measure the difference between individual vehicle operating speed and the design speed for the location. The results from two case studies support the use of error-adjusted GPS probe data for identifying sites where safety at a given location is compromised by driving too fast for the underlying geometric restrictions. Locations with higher TSPI values were found to correspond closely to sites with a higher number of speed-related crashes as reported over a period of five years. The results from the two case studies were found to be consistent in linking GPS probe estimates of TSPI to locations of higher crash risk.
