Evaluation of inexpensive global positioning system units to improve crash location data

The state of Alabama stores and manages detailed information about vehicle crashes including their approximate locations. Currently, crash locations are estimated and hand recorded by highway patrol officers at the scene of a crash. These locations are typically placed at identifiable points along the roadway, such as mileposts and intersections. The resulting resolution can place vehicle crashes caused by the same roadway variable as far apart as 2 km, making accurate identification of roadway safety hazards difficult. The research project was initiated through the University Transportation Center for Alabama to improve vehicle crash analysis through accurate and inexpensive collection and display of crash locations. The research employed Global Positioning System (GPS) and Geographic Information System (GIS) technologies. GPS units ranging in price from $130 to $3,400 were evaluated on the basis of cost, accuracy, usability, additional equipment needed, and time required to collect a location. From this analysis two GPS units were selected: (a) a handheld unit, the Garmin GPS 12 Map, and (b) a computer-based unit the Rand McNally Streetfinder Deluxe. With the recent removal of selective availability, the research has shown that inexpensive GPS units tested are capable of locating a vehicle crash within an 8-m radius. In addition, both an off-the-shelf GIS and accurate basemaps were employed to display the new GPS crash data. By analyzing GPS locations in a GIS, "hot spots" where multiple crashes occurred were identified through buffering operations. An analysis of actual crash location data showed that GPS data provided more information about a crash than conventional methods, specifically at interchanges and along roadway segments.