Naturalistic Driving Study: Linking the Study Data to the Roadway Information Database

Abstract

This report details the methodology used to link the second Strategic Highway Research Program (SHRP 2) Naturalistic Driving Study (NDS) data to the SHRP 2 Roadway Information Database (RID), the final critical step in completing the SHRP 2 Safety database. The NDS data set contains extensively detailed data collected continually from more than 5.5 million trips taken by the instrumented vehicles of 3,147 volunteer drivers in six sites. The RID contains extensively detailed data on 25,000 centerline miles of roadways in these six sites, less detailed data on 200,000 centerline miles of roadways in the six states in which the sites were located, and supplemental data on topics such as crash histories, travel volumes, construction, and weather in the six states. The true power of the NDS and the RID comes when they are linked—when each trip is matched to the roadway segments that were traveled and each roadway segment is matched to the trips that traveled on it. The matching methodology documented in this report uses as input the GPS position data collected once per second by the NDS instrumentation and the NAVTEQ network of road segments of all public roads in the continental United States over which the NDS vehicles could travel. The Matching Algorithm associates each GPS point of an NDS trip with the road segment on which a vehicle traveled. The principal challenges overcome by the algorithm were to accommodate GPS readings that may drift far from the correct roadway and to be operationally efficient in comparing the 3.7 billion GPS readings with the 2.6 million NAVTEQ road segments that were traversed. The algorithm’s results are stored in a very large table that associates trip timestamps with road segments.