Book Description

Countermeasures for motor vehicle crashes are often determined after extensive data analysis of the crash history of a roadway segment. An important factor that drives the value of this analysis is the accuracy, or precision, with which the crash is located. Yet this location is only as accurate as the estimate of the police officer. In light of this, many have suggested that global positioning system (GPS) technology has the potential to increase data accuracy and decrease the time spent recording crash location data. Over 10 months, the locations of 34 crashes were determined using both the conventional method and a hand-held GPS receiver. The two methods were compared in terms of timeliness and precision. The benefits of any improved precision using the GPS were assessed through querying crash data analysts at the local level as to how the improved precision affected their consideration of potential crash countermeasures for five crashes selected from the sample. At the scene of the crash, the use of GPS receivers added up to an average of 10 extra minutes per crash, depending on how crash location was defined. There was an average disparity of 130 ft (39 m) between the location as determined with the GPS and conventional methods, presuming the GPS precision given in the literature is within 7 ft (2 m). However, although both the literature and survey responses revealed that greater precision will affect evaluation of crash countermeasures in some instances, many of the errors cited in conventional crash location methods arise from human error rather than precision. The authors provide recommendations for defining crash location uniformly, limitations of the methodology employed in this effort, and the types of countermeasures that may or may not benefit from improved precision.