Originally Posted by ImolaRedM' post='617030' date='Jul 5 2008, 02:13 PM

By keeping speed limits artificially low most people drive at the speed they feel are safe, while a few will obey the limit regardless and drive 55mph. This leads to increased speed variance. So if the 85th percentile of traffic is doing 70mph but you have a limit of 55mph then you're increasing the variance and therefore increasing the risk of accidents. Increasing the limit in this case to 65mph or 70mph would actually improve safety.



Speed variances of more than 15mph are unsafe. I didn't state that people drive 15mph over the speed limit. In fact, it has been shown that most people drive at a speed they feel comfortable with (85th percentile). Posted speed limits have not proven effective at abating speeds. To reduce speeds other tactics have been shown to be effective. These include painting wider lines in the road to make the lanes appear smaller, narrower shoulders on the roads, and narrower lanes.



If the 85th percentile speed limit for a given stretch of road has been determined to be 85mph then most drivers will drive at the same speed thus reducing variance. Remember, studies show that speed variance is a greater contributor to accidents. You are arguing accident fatalities and that's another topic. I'm not arguing against the laws of physics but against the statement that lower speed limits save lives. Another way to look at this is that statically, we have had fewer fatalities per million miles driven in the US in the 1990's after the repeal of the National Speed Limit than we did in the 1980's during the height of the National Speed Limit.