Evaluation of the Accuracy of GPS as a Method of Locating Traffic Collisions

Abstract

The objectives of this study were to determine the accuracy of Global Positioning System (GPS) units as a traffic crash location tool, evaluate the accuracy of the location data obtained using the GPS units, and determine the largest sources of any errors found. The analysis showed that the currently used GPS unit is capable of obtaining accurate latitude and longitude data at a crash site that would allow the site to be properly located. However, substantial differences were found between the location of some crashes as identified with the GPS and milepoint (CRMP) data. Of a sample of 100 random crashes, 55% were found to have an accurate GPS reading and 58% were found to have an accurate CRMP location. There was a large range in the difference between the GPS and CRMP data by county and police agency. This shows both the accuracy that can be obtained with proper training and use as well as the lack of proper training and/or use of the GPS units at some jurisdictions. The source of errors found for the GPS data was related to the operator rather than the equipment or environment. The actions necessary to significantly improve the accuracy of the GPS data are manageable and relate to training, proper use of the GPS unit, care when placing the GPS data onto the crash report, and a minor modification to the crash report. The source of errors related to the CRMP data primarily dealt with improper interpretation of the milepoint log, inaccurate use of the available mileposts and lack of knowledge of current data available. A few edits of the crash data could be used which would significantly improve the accuracy of both the GPS and CRMP data. Recommendations were made to improve the accuracy of both GPS and CRMP data. These included additions to the GPS procedure pamphlet, a minor modification to the crash report, additional training in the use of the GPS unit, providing up-to-date milepoint logbooks, and using an edit which checks the accuracy of the GPS and CRMP data.