The Historic Evidence Shows 20mph Blanket Speed Limits are not Effective
Frequent calls from road safety fanatics for 20 mph speed limits ignore historic evidence.
There are now frequent calls from road safety fanatics for 20 mph speed limits to be imposed on all suburban roads, even major "A" roads that run through towns and cities. But the historic evidence is being ignored. Before 1930 Great Britain had a blanket 20 mph speed limit across the whole country. But road deaths in the year before this limit was abandoned were about 7,300 compared with about 1,900 in recent years. They also fell in the years immediately after 1930 when they had been rising before.
So the moral is surely that wide area speed limits are ineffective in reducing road traffic accidents and that simply putting up signs without road engineering or other measures will have negligible impact on casualties. That is exactly of course what the Department of Transport used to say.
No doubt there were some people who ignored the increasingly unrealistic 20 mph limit back in 1930, as there are some today. But the ABD has always argued that speed limit setting should be based on the 85th percentile of free flowing traffic speed which has been demonstrated to be both the safest speed and the one that encourages compliance. The ABD is not opposed to local 20-mph zones in residential streets where traffic speeds are already near that limit or can be engineered to be so (without speed humps). But expensive wide-area, sign-only schemes are not likely to be cost-effective and will have a negligible impact on actual traffic speeds, as has been well documented. Money is being wasted on such schemes which could be much better spent on other road safety measures.
Let's have a halt to the polemics from 20mph supporters, and get some real science back into road safety.
ABD Chairman Brian Gregory had this to say only recently:
“As with most pet road safety ideas proposed by amateur enthusiasts — speed humps, speed cameras, etc — there is little attempt to collect scientifically sound evidence of the benefit of such ideas. No proper controlled, "double-blind" trials are undertaken. The enthusiasts rely on the strength of their rhetoric and the use of selective data to make their case. Don't be fooled by these methods but look at the facts. And remember that all road safety schemes should be cost justified because if there are better things to spend the money on, then that is where the limited funds should be spent.”
Road traffic fatalities in Great Britain from 1926 to 2010 are given on pages 5/6 of the report entitled "Reported Road Accident Statistics" from the House of Commons Library (see www.parliament.uk/briefing-papers/SN02198
). The increase in the years of World War II is known to have arisen from people driving in the black-out without lights.
Information on the 1930 Road Traffic Act
(which abolished all speed limits for cars) and the preceding 1903 Act
which set a 20-mph limit. [Wikipedia]