Infrastructure and safety for cheap

November 27, 2011

I had recently become aware of how sharply the danger to pedestrians from car crashes rises with speed, but this post at Copenhagenize makes the point clearly, with pretty pictures. The risk of death at 20mph is only 5%, but rises to 45% at 30mph.

The only point missing is how dangerous (to others) it is to “fudge” the speed limit. 22 in a 20, that’s not really speeding, is it? Use a very conservative estimate of increased risk for small speed increases (exponential between 20 and 30mph), each 2 mph increase in speed compounds 55% onto the risk — so 22mph has a 7.8% risk, 24 has 12%, 26 has 19%, and 28 has 29%. It’s a big deal.

The flip side of this is that adding safety is really cheap; just establish low speed limits where cars might crash into pedestrians, and enforce them, and you’ve made the roads far safer.

The Urban Country describes an experimental bike lane made by anonymous stencil artists and other people working with a small collection of trash to mark the “lane”. A woman died at this intersection because a truck lazily cut the corner close and crushed her. Yet, with paint and trash, we discover that there is plenty of room for traffic and trucks, and there is plenty of room for them to turn with space reserved for bicycles, and people will pay attention to an incredibly ad hoc bike lane. It’s sadly late for her, but now that we know how easy it is, what’s stopping our allegedly safety-minded road departments?

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