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More killed and injured is almost better say safety campaigners

Controversial 20mph speed limits in residential streets may not bring any significant improvement in road safety, a report published by the Department for Transport has found
An analysis of the UK's first city-wide scheme - in which the limit was lowered from 30mph to 20mph on all residential streets in Portsmouth, at a cost of £500,000 - found that it has not brought any significant reduction in the number of accidents.
The number of people killed or seriously injured on affected roads actually went up, not down, after the limit was lowered.

So that "significant improvement" and "significant reduction" actually turned out to be an increase - I don't know if it is a "significant" increase but stop using the bloody weasel words. It failed.


Assuming they have a count of all the accidents etc. then if the number went down, it went down. The much overused term, significance, means nothing.

If you are stupid enough to take a small sample (like, a parish or a few roads) then you have sampled and by saving time in counting you have raised uncertainties in how representative that sample is.

But if you have a total count, predefined as to the area covered, etc. etc. then the data is the data is the data.

If it went up, it went up.

If it went down, it went down

Thanks for flagging this. But isn't the bigger story here the fact that the report found no need for speed limits in the first place?


I'm a petrolhead, a carfreak, but.. the 20mph thing is working well here in south Bristol. The streets are les intimidating and really, isn't 30mph in residential areas just too fast??

To anyone who has studied the research and who understands the psychology, this is not at all surprising.

To simplify greatly, there are two sorts of drivers:
(1) Those that are quite happy to break the 30 mph speed limit. They will not be affected by a 20 mph limit except that they will now have a greater speed differential from other traffic and, hence, be more frustrated. They will cause more accidents.
(2) Those that will abide by the law. They will be vulnerable to more attention deficit and/or frustration and guess what the result will be.

Seat belts are similar. They increase accidents and have no significant effect on death or serious injury rates. (Hint: the relevant research is not the well-publicised stuff showing dummies in test impacts. It is the effect of increased security on driving behaviour.)

Remember also that the person with the greatest interest in avoiding accidents is the driver. The trick is to make him concentrate on controlling the car.

Let me tweak that comment-The motorists have been significantly inconvenienced for no good reason, and GBP500,000 has been demonstrably wasted. We could not be happier. Four wheels bad, two wheels good.

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