The objective of this study was to document the change in operating speeds of cars and trucks on rural interstates and parkways as a result of the change in speed limit from 65 mph to 70 mph. The 85th percentile speed increased 1.3 mph for cars (74.6 to 75.9 mph) and 0.6 mph for trucks (69.8 to 70.4 mph) on rural interstates and 2.0 mph for cars (73.5 to 75.5 mph) and 1.2 mph for trucks (69.5 to 70.7 mph) on four-lane parkways. The increase in speed limits on a limited number of roads did not result in an increase in speeds on other highway types. There is a large difference between the 85th percentile speed and posted speed limit on non-interstate and parkway roads which were designed to accommodate higher speeds.

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