26 February, 2007

I Can't Drive 55

... and, according to the Colorado Department of Transportation (PDF warning), we shouldn't really have to. (Leaving aside the fact that most freeways in the Denver Metro area have a speed limit of 65 rather than 55. Sheeesh, can't a guy have fun with his titles every so often without nitpickers?) Emphasis mine:
It is a popular misconception that reducing the speed limit will automatically slow the speed of traffic, while raising the speed limit will automatically cause an increase in the speed of traffic.

“Before and After” speed studies show that there are no significant changes in vehicle speeds after speed limits are changed. “Before and After” accident studies usually do not show any significant change in accident rates after speed limits are increased or decreased. National studies go further and say that “it is generally at the upper boundary of a speed range where crash involvement rates are lowest.”
Traffic investigations have shown that most people will drive the roadway as they perceive the conditions and will ignore a speed limit that is unrealistically too low or too high. A realistic speed limit is voluntarily obeyed by the reasonable majority and more enforcement effort can be applied to the unreasonable few who drive too fast or too slow.

An unrealistic speed limit with is too slow will:
  • A) Make the behavior of the majority unlawful;
  • B) If enforced - cause antagonism toward enforcement personnel and traffic laws in general;
  • C) Create a bad image of the community for visitors and tourists;
  • D) Result in speed differentials in the traffic flow.

An appropriate, “just right” speed limit will result in the maximum number of vehicles traveling at about the same speed, thus reducing conflicts caused by speed differentials.
The 85th percentile speed, that speed at or below which 85% of the traffic is moving, is widely accepted as being closest to that “just right” speed limit - a case of Majority Rule. Of course, other Traffic Investigation factors must be taken into consideration.
To just about anyone who has a heavy foot, unreasonable speed limits on interstates and open freeways have been bones of contention since the days when the interstate freeway system was still just a dream in old man Eisenhower's eyes. This becomes doubly true when almost everyone on a particular stretch of freeway is going a good degree faster than the posted speed limit. Speed limits just about everywhere as then degraded to the point where only police armed with radar/laser speed detectors actually care about how fast people are going.

This becomes a Very Bad Thing when you start talking about places where speed limits actually have sound public-safety reasoning behind them. School zones. Residential areas. Business districts. Other high pedestrian population areas. Those are the places where speed limits are firm necessities. Yet due to the barest of nods the population gives to speed limits in general, these needed limits are painted with, then blatantly ignored by, people wielding the same broad brush.

Even the National Cooperative Highway Research Program (another PDF warning, see page 88), as part of the Transporation Board of the National Academies, says that (Emphasis mine again.):
a review of available speed studies demonstrates that the 85th percentile speed is only used as a “starting point,” with the posted speed limit being almost always set below the 85th percentile value by as much as 8 to 12 mph.
And from an earlier bullet point:
Several studies have demonstrated that 85th percentile operating speeds typically exceed posted speeds. These studies also show that the 50th percentile operating speed either is near or exceeds the posted speed limit.
This is a bad thing. When you set the barrier of "What is legal?" well below the line of "What is normal/average?", you create a situation where people will continue to break the law due to their normal everyday behaviors. This does not change behavior like some of the supporters of lower-speed-limit laws would suggest, but instead creates the aforementioned resentment towards the law in any of its various guises.

Adjusting the posted speed limits, if only on interstates and open freeways, to the point where 85% of people are in compliance... That's a good thing. And the bureaucrats in CDOT deserve a pat on the back for recognizing it.

Will it end speeding? Doubtful. Especially doubtful for as long as I personally possess a legal driver's license. What it will do is keep my fellow lead-foots from the opinion that all speed limits are far too arbitrary and, therefore, all speed limits should be ignored. And ignoring laws is never a good thing when you live in a society based on the rule of law.

Now if you'll excuse me, I need to go borrow my friend's car. Might as well do what I can to raise the 85% mark a little bit higher, no?

[Turn Signal: Joshua Claybourn]

1 comment:

Garth Wilson said...

Congrats Jake! This entry earned you some credit in Today's Post.