Vehicle speeds are a crucial factor in traffic safety. NHTSA estimates that speeding is involved in approximately 31% of fatal motor vehicle crashes, costing society over $40 billion per year. Since speeding is such a pervasive traffic safety issue, NHTSA funded two field surveys to measure driving speeds for all types of motor vehicles on freeways, arterial highways, and collector roads across the United States, to produce national and regional estimates of travel speeds for various types of roads and vehicles, and track these speed measurements over time. The speed surveys were designed as geographic cluster samples of primary sampling units (PSUs), which 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 on randomly drawn road segments on limited access highways, major and minor arterial roads, and collector roads. Speed measurement sites were selected in road segments with various degrees of straight, curved, flat, and hilly geometry. Twenty to 60 sites were selected in each PSU. Speed data were collected during spring and summer 2007 and spring 2009. Speeds were measured using small, self-contained, on-road sensors temporarily placed on the road surface for a single 24-hour period at each site. In 2009, side-fire radar devices were used on the limited access highways to enhance safety in data collection. About half of the observations were free-flow vehicles. Mean, 85th percentile, and other measures of traffic speeds and speed variation for free-flow traffic compared to all traffic, did not differ by more than 1.4 mph for 2007 and 1.5 mph for 2009. (Author/publisher) For the complete report, DOT HS 811 638, see http://www.nhtsa.gov/staticfiles/nti/pdf/811638.pdf
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