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Time: 8:51:06 PM
Remote Name: 220.127.116.11
This is how I remember it….
The Institute's frequent monitoring of free-flowing travel speeds on interstate highways where the 55 mph speed limit was retained and speeds on roads where limits have been raised to 65 mph shows that, in general, higher speed limits lead to greater proportions of cars traveling faster than 70 mph. For example, in New Mexico, the first state to raise its limits to 65 mph on rural interstates, the proportion of motorists exceeding 70 mph grew from 5 percent shortly after speed limits were raised to 36 percent in 1993. On urban interstates that stayed at 55 mph, only 13 percent of cars and 2 percent of tractor-trailers traveled faster than 70. In Maryland, which retained 55 mph limits, the proportion traveling faster than 70 mph remained virtually unchanged at 7 percent during 1988-93. By 1994, 12-15 percent of cars were exceeding 70. In neighboring Virginia, which switched to 65 mph limits, the percentage exceeding 70 mph went from 8 percent in 1988 to 29 percent by 1992 and 39 percent by 1994.
First, it is not clear from the paper whether the authors assumed that all states changed their speed limits in April 1987 and then again in December 1995. An assumption of uniform intervention dates across all states creates issues with their analysis. While many states did change their speed limits as soon as they were legally able, many other states did not enact a higher speed limit until much later. For example, Virginia did not choose to raise its speed limit to 65 miles per hour (mph) on rural interstates until July 1988 (Jernigan et al. 1994). Louisiana did not increase its interstate speed limit to 70 mph until August 1997 (USDOT NHTSA 1998). If these time periods were not correctly categorized in the analysis, the results could be inaccurate. It is not clear whether the authors changed the intervention dates on a state-by-state basis or used a uniform intervention date for all states. In 1987, states were permitted to increase speed limits on rural interstates to 65 mph. This created a uniform speed-limit change in those states that chose to increase speed limits. -----------------------------------
Kari, do you recall the discussion we had on this board about the construction problems you mentioned? Didn’t someone who lived in the areas write that if you knew the area you could take another route to bypass the traffic? –Jasper