Tuesday, October 12, 2010

Anti Speed Camera Arguments #6: Does Speed Kill ?

Safespeed believe that there has been a trend for speed limits to be lowered without evidence that lowering them will reduce crashes. They believe that speed limits "should never be used to attempt to modify the speed of traffic" and that the claim that "accident risk simply increases with speed...is false". However, they do "welcome properly set speed limits, and welcome speed limit enforcement when speed limits are exceeded in a way that causes danger". (source) Those statements don't sit well together. If you say "you should never attempt to modify the speed of traffic using speed limits", then how would you slow traffic if it is fast enough to cause danger? Their Road Safety Manifesto should give us a clue: it concentrates on "driver training", "road safety culture", and "road safety information should be regularly aired on TV at peak viewing times". Their Manifesto doesn't cite any evidence that any of this will work. It's all supposition and wishful thinking.

Meanwhile, back in the real world:

There is some interesting Dutch research here. It studies the effect of reducing motorway speed limits from 120kph or 100kph to 80kph, accompanied by strict enforcement. The reason it is interesting is that speed limits were reduced not to reduce crashes, but to comply with air quality legislation. So the 'regression-to-mean' effect that Safespeed usually use to cast doubt on the correlation between lower speeds and lower crash rates does not apply. The study says "The effects at A13 Overschie were spectacular (empirical results): the number of accidents decreased by 60% and the number of victims by 90%. Besides, no indications were found of compensatory behaviour (drivers who speed up downstream). The increased safety was caused by lower speeds and lower speed differences."

Futher research: Nilsson (1982) researched speed limit changes from 110 to 90 km/h on Swedish roads. He compared changes in accident risks with roads where the speed limits had remained unchanged, and reported the statistical relations (the regression model) of speed (limits) and accidents. This model is now well-known as the Nilsson formulas. You can read about it here.

But is speed in itself correlated with increased crash risk? According to the EU's road safety experts, "A higher speed increases the likelihood of an accident. Very strong relationships have been established between speed and accident risk: The general relationship holds for all speeds and all roads, but the rate of increase in accident risk varies with initial speed level and road type. Large speed differences at a road also increase the likelihood of an accident. In addition, drivers driving much faster than the average driver have a higher accident risk; it is not yet evident that this is also the case for the slower driver."

1 comment:

  1. i won $1,000,000 in the powerball lottery, I took an advice from some person who talked about this great spell caster called Dr Iyaryi the person placed a testimonies on a blog saying how Dr Iyaryi helped him win the lottery by sending him the winning number i was curious and i thought it was all joke not until i contacted this spell caster to know for myself how this work cause i have spend a lot buying tickets and i never win. I contacted him and he told me the necessary thing that need to be done and i did it and he told me to wait for 3days and truly he gave me the winning numbers to play the lottery which i did, Can you believe my name was the first among winners. He told me (my son all i need you to do for me is make sure that you share this testimonies to others so that they can also win the lottery cause i do not have much time to spell on the internet) so that is why i am sharing this testimony with you that if you want to win the lottery this is the way online tips can not help you driayaryi2012@hotmail.com is the only answer to that your problem of winning the lottery