United States Department of Transportation
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Alternative Title:National Traffic Speeds Survey III: 2015
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Abstract:Vehicle speeds are an important factor in traffic safety. NHTSA’s most recent data estimates that approximately 27 percent of all fatal motor vehicle crashes are speeding-related (NCSA, 2018). NHTSA estimated the economic cost of speeding-related crashes to be $52 billion in 2010 (Blincoe et al., 2015). This is the third of three field surveys NHTSA has funded in response to this pervasive traffic safety problem. The surveys measured driving speeds for all types of motor vehicles on freeways, arterial highways, and collector roads across the United States and produced national and regional estimates of traffic speeds for various types of roads and vehicles, tracking these speed measurements over time. The speed surveys were designed as geographic cluster samples of primary sampling units (PSUs). PSUs can be a city, county, or group of two or three counties. PSUs were chosen to represent a range of combinations of regions of the United States, level of urbanization, and type of topography (flat, hilly, mountainous). Speeds were acquired from randomly drawn road segments on limited access highways, major and minor arterial roads, and collector roads (FHWA, 2013). Speed measurement sites were selected in road segments with various degrees of straight, curved, flat, and hilly geometry. Thirty sites in each of 24 PSUs were selected, for a total of approximately 720 collection sites. Speed data was collected during summer 2015. The previous survey was in spring 2009. Speeds on major and minor arterials were measured using small, self-contained, on-road sensors temporarily placed on the road surface at each site for a single 24-hour period. Side-fire radar devices were deployed on the limited access highways to enhance safety and efficiency in data collection. “Free-flow” was defined as vehicle headway of greater than 5 seconds, indicating vehicles with fewer constraints on speed choice due to the proximity of other vehicles. As in 2009, the mean, 85th percentile, and other measures of traffic speeds and speed variation for free-flow traffic did not differ by more than 1.5 mph in 2015, compared to all traffic.
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