The first site listed in table 12 is a small urban area roadway with a posted speed limit of 35 mi/h (56 km/h). The site is located between 2 experimental sites where the speed limits were lowered from 50 to 45 mi/h (81 to 72 km/h). The next 2 sites listed in table 12 are located in a small city at each end of an experimental section where the speed limit was lowered from 45 to 35 mi/h (72 to 56 km/h).
The fourth site given in table 12 has a posted speed limit of 40 mi/h (64 km/h) and is contiguous to a rural experimental section where the speed limit was raised from 40 to 45 mi/h (64 to 72 km/h). The last site in table 12 is located in a small town adjacent to an experimental site where the speed limit was raised from 30 to 35 mi/h (48 to 56 km/h).
As can be seen by examining table 12, there were very few, if any, effects on the mean, standard deviation of speeds, or 85th percentile speeds at these locations after the speed limits were changed on the experimental sites. The examination of the speed distribution and vehicles following at headways of less than 2 s revealed similar results. The accident sample was too small to provide meaningful results.
Overall, there were very few driver behavior changes on any of the contiguous and adjacent roadways after speed limits were altered at the experimental sites.
Table 12. Indirect speed effects at contiguous sites. ---------------------------------------------------------------------------- Posted Before After Differences Speed Experimental Mean Std. 85th Mean Std. 85th Mean Std. 85th Limit Section Speed Dev. Pct. Speed Dev. Pct. Speed Dev. Pct. mi/h Change mi/h mi/h mi/h mi/h mi/h mi/h mi/h mi/h mi/h ---------------------------------------------------------------------------- 35 50 to 45 42.3 6.4 49 42.3 6.9 49 0.0 0.5 0 45 45 to 35 47.1 8.4 55 47.1 7.3 55 0.0 -1.1 0 45 45 to 35 41.0 8.5 50 41.1 8.4 50 0.1 -0.1 0 40 40 to 45 47.0 4.8 52 46.5 4.9 51 -0.5 0.1 -1 35 30 to 35 34.7 6.9 42 35.3 6.5 42 0.6 -0.4 0 ---------------------------------------------------------------------------- 1 mi/h - 1.61 km/h
Next: Effects on a Sample Interstate Sections | Prev: Effects on Accidents | Contents