So why not set speed limits based on that? The answer is twofold: (a) locals along the road want a slower limit because they think it will actually make people drive more slowly, and (b) cities and their police departments want a slower limit because they know that people will still drive faster, leading to speeding ticket revenue generation.
(h/t +Yonatan Zunger)
Reshared post from +Kirill Grouchnikov
Traffic engineers believe that the 85th percentile speed is the ideal speed limit because it leads to the least variability between driving speeds and therefore safer roads. When the speed limit is correctly set at the 85th percentile speed, the minority of drivers that do conscientiously follow speed limits are no longer driving much slower than the speed of traffic. The choice of the 85th percentile speed is a data-driven conclusion — as noted Lt. Megge and speed limit resources like the Michigan State Police’s guide — that has been established by the consistent findings of years of traffic studies.
Is Every Speed Limit Too Low?
Americans nearly universally speed, and excess speed is a factor in many accidents. But what if higher speed limits made roads safer?
I'm pretty hard-nosed about not speeding. There's nothing so important that I need to get to that speeding is required. If I'm late it's because I didn't plan appropriately and speeding isn't a solution for poor planning. That said, people who drive under the limit by 5 MPH or more set my teeth on edge. Just because I'm obeying the law doesn't mean I want to dawdle along the way.
I tend to go 5-7 above the speed limit, which seems to fall comfortably into the flow of traffic but is low enough to not draw attention.
I'm in agreement about the 85/15 rule for major roads. On residential streets, I'm in favor of keeping slower speed limits (<25) for the safety of pedestrians (particularly children).
+James D. The argument of the article, though, is that people will travel what they will travel, regardless of the posted sign. If you want to keep them slower, you need to do something to make them go slower — speed humps (or dips), flashing signs, you-are-traveling signs, frequent ticketing, etc.
It's interesting to me how little morality comes into play with speed limits. Most are not set arbitrarily. You may not agree with them, but there are reasons why they're set at a certain speed. You'd think truly moral people would obey the law, but the evidence against that is overwhelming.
People who drive faster than you are maniacs; people who drive more slowly than you are idiots. -George Carlin
It is, perhaps, a combination of (a) rejecting imposed morality for one's personal judgment and (b) the quality of risk assessment skills on the parts of individuals drivers (both in terms of judging what the speed on a road is safe, and what the likelihood of a given risk is).
So, most drivers will slow when they see kids playing, but if they don't see kids they may drive faster than even they would consider safe if kids suddenly appeared.
Don't most drivers believe that they themselves are above average? (A statistical impossibility.)
+John E. Bredehoft Yup (on both counts).
I tend to drive at or very close to the limit on controlled access roads (freeways, thruways, etc.,) and where conditions such as the design of the road, congestion, etc., seem to dictate that the limit is very prudent.
Strangely, there is one stretch on my work commute where I drive about 39 – 41 mph in a 35 mph zone. Why?
The reality is that not only do I feel that it is appropriate for that stretch (and I am never the fastest vehicle) but because it seems to be the most fuel efficient.
As with a lot of recent vehicles, my '09 CR-V displays my fuel efficiency, both the trip average and current. I am sort of addicted to the challenge of achieving the best mileage I can.
I definitely am above average. 😀