A field survey was conducted during spring and summer 2009 as a longitudinal repetition to a similar effort undertaken in 2007. The goal was to measure travel speeds and prepare nationally representative speed estimates for all types of motor vehicles on freeways, arterial highways, and collector roads across the United States. Over 10 million vehicle speeds were measured at 627 sites included in the geographic cluster sample of 20 primary sampling units (PSUs). Each PSU was a city, county, or group of two or three counties representing 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 low, medium, or high degrees of horizontal and vertical curvature or gradient. Overall, speeds of free-flow traffic on freeways averaged 70.5 mph and were approximately 17 mph higher than on major arterials, which at 53.3 mph were in turn about 6 mph higher than the mean speed of 47.0 mph on minor arterials and collector roads. Most traffic exceeded the speed limits. Seventy-one percent of traffic on limited access roads and about 56% of traffic on arterials and collectors exceeded the speed limit. About 16% of traffic exceeded the speed limit by 10 mph or more on freeways, arterials, and collector roads. Speeds of passenger vehicle size classes were generally higher than for medium trucks. (Author/publisher)
Samenvatting