Speed Limits Should Reflect Neighbourhood Safety, Not Driver Preference

By Nicholas Kevlahan
Published October 19, 2012

A September 28 Globe and Mail editorial arguing that lower automobile speed limits allow for more livable neighbourhoods makes a very interesting point:

Speed breaks the calm, and neighbourhoods should be calm. That feeling led London [UK] to set a speed limit of 20 miles an hour (a little more than 30 kmh) in 400 neighbourhood zones since 2001. Research published in the British Medical Journal found a 46 per cent drop in deaths and major injuries in the zones.

Yet here we are in Ontario, debating a law that would mandate bicycle helmets, so cyclists might have a better chance of surviving the crashes made inevitable by the design of our roads!

(And there is no problem interpreting this very straightforward statistic: lower speed limits led to a significant drop in deaths and major injuries.)

Are the limits set for safety for all road users? No, they are set by the speed at which drivers actually want to drive:

"Traditionally, speed limits have been set by traffic engineers using samples of actual speeds and calculating the 85th percentile speed," says the Transportation Association of Canada. Drivers are the last group who should be setting their own limits - as drivers would be the first to admit.

Nicholas Kevlahan was born and raised in Vancouver, and then spent eight years in England and France before returning to Canada in 1998. He has been a Hamiltonian since then, and is a strong believer in the potential of this city. Although he spends most of his time as a mathematician, he is also a passionate amateur urbanist and a fan of good design. You can often spot him strolling the streets of the downtown, shopping at the Market. Nicholas is the spokesperson for Hamilton Light Rail.


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By Pxtl (registered) - website | Posted October 19, 2012 at 11:13:57

Are the limits set for safety for all road users? No, they are set by the speed at which drivers actually want to drive.

Unless you're planning on putting speed governors in all our cars, this is exactly as it should be. Driving is as much operated by instinct and muscle memory as it is by conscious thought. Putting up signs with numbers on them won't change the way people naturally drive on the road, they'll just do it illegally and occasionally get busted for it.

If you want to slow down traffic, you have to design roads for slow traffic. If the road feels fast, people will drive fast.

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By kevlahan (registered) | Posted October 19, 2012 at 11:45:17 in reply to Comment 81977

I absolutely agree. But the problem is that traditionally the roads are also designed to be safe for drivers at speeds significantly greater than the posted speed, which leads to a lot of speeding (look at the curve radii and lane widths on many 50km/h roads in Hamilton).

The solution is to design roads so that drivers naturally drive at lower speeds.

This is being done extensively in Europe, and is beginning in Canada.

Examples include narrowing lanes (which have the added benefit of allowing wider sidewalks, cycle lanes or more parking), tight turning radii, two-way conversion, adding obstacles (bump outs, speed humps), chicanes, and locally narrowing to one-lane on two-way roads forcing drivers in one direction to yield to oncoming traffic. Unfortunately, Ontario has been quite timid so far in implementing many of these techniques and even 30km/h zones remain controversial.

A reduction in speed limits to 30km/h needs to be accompanied with these sorts of changes to bring the 85th percentile naturally down to 30km/h. Enforcement alone doesn't work.

But the speed limit does need to come down even once the road is calmed since, as the editorial notes, drivers do tend to interpret speed limits as minimum speeds, and assume the true limit is about 10km/h faster.

Comment edited by kevlahan on 2012-10-19 12:47:32

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