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Bike Adelaide: Perceptions (about speed limits)

April 11, 2010

A recent article in the Advertiser suggests that over half of South Australian drivers routinely disobeyed the 50 km/h default speed limit. The findings come from a report published by the University of Adelaide Centre for Automotive Safety Research.

What interested me were most of the responses. 219 people took the trouble to respond. I did not have the time to read every single one but of those I did, the vast majority say that the rate of disobedience is merely proof that speed limits are too low. The evidence is overwhelming of course that lowering the speed limit saves lives. See for example the recent study in the British Medical Journal.

I think it comes from people’s perceptions. If you travel everywhere by car, as many people in Adelaide do, your view of the world is generally behind a windscreen. Your views on traffic congestion come from the line of cars you see from behind the steering wheel.

If you travel by bike, bus or on foot, you get a very different picture. A road on which everyone is travelling at 60 km/h or more is very different indeed from one on which people are travelling at 40 km/h or less. For one thing, the second one is a lot less stressful.

One misconception that comes out in the comments is the assertion that lower speed limits slow down traffic and cause congestion. Both are wrong. If you watch a line of cars move off from a red light, it is a bit like watching an old freight train. As the locomotive moves away, the couplings tighten and the first truck moves. The second follows until slowly but surely the whole train is moving but it is longer because of the stretched couplings. It is the same with traffic except instead of couplings you have gaps between cars. The size of the gaps depends on the speed of the traffic. The faster a car travels, the more space it takes up because of the required braking distance.

Slowing cars a little reduces the required braking distance and increases the number of cars that can pass a particular point in a given time because each car is taking up less space. In other words, it actually can increase the carrying capacity of the road.

It is funny though that an article like that leads to so many people commenting that way. It is an example of what has been described as car head.

If you have an article about cyclists breaking the law by riding on the pavement, the reactions are generally different. Then you see phrases such as “lycra louts” and “law unto themselves”. What must be recognised is that cycling on the pavement or through red lights is a symptom of unpleasant cycling conditions and poor cycling infrastructure. In a city like ours that is built around motoring and full of reckless, risk-taking drivers (over half of which routinely break the speed limit if the Advertiser is to be believed), cyclists understandably do all they can to stay safe. That includes riding on the pavement.

If some serious money was spent on proper, safe, separated cycling infrastructure that made it easy to get around by bike instead of the constant obstacles they face, the story might be different.

Edward writes this blog called Bike Adelaide. He writes well and finds good angles on cycling in Adelaide (and cities in general)

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