Getting It Wrong in Montogomery County
As was recently reported in the Washington Post, Montgomery County, Md., is planning an overhaul of its “road code,” the sort of thing that seems like a bureaucratic footnote but then goes on to have major implications in the built environment.
Among the major issues, the newspaper reported:
The panel recommended that roads in urban areas be designed for speed limits of 30 to 40 mph, saying anything slower would be unrealistic and difficult for police to enforce. The panel also said trees should be planted farther from curbs on roads with 40 mph speed limits because of the danger they pose to motorists who hit them.
What strikes me in discussions like these is the weird disconnect between design and driver behavior. One of the reasons it can so often be difficult to enforce lower speed limits is that these limits are posted on roads that are intensely over-engineered. The supposed “fix,” as suggested above, is to assume that drivers are going to drive at a certain speed, and so to then rearrange the entire landscape — removing trees, etc. — to allow them to do so “safely.”
Of course, on the road “designed” for speed limits of 30 to 40 mph, they will inevitably drive faster. But then, of course, if someone crashes and kills a pedestrian or another driver, it’s an “accident,” it’s down to driver behavior; if they smash into a tree, it’s deemed poor traffic safety engineering. As the work of Eric Dumbaugh has found, looking at streets like the one above, at Stetson University in Florida, often the worst safety performance comes on the roads that are deemed “safe” by traffic engineers, while the best can come on tree-lined streets like the one above (which had no crashes and speeds below 30 mph during the five years he looked at it).
We consistently get urban speeds wrong in the U.S. In Germany, the land where speed is supposedly worshipped, the speed-limit free sections of the autobahn are contrasted by a mandatory, heavily enforced 30 KPH (that’s 18 mph, folks) limit in residential areas.
Another classic specter the article invokes is emergency response times. Any time a group seeks to lower speeds on a road, there are dark projections made of people being killed in fires because firefighters will be held up on traffic calmed streets. Well, for one, have you ever seen these vehicles on the way to an incident? They often don’t actually drive that much faster than anyone else — particularly since cars frequently don’t get out of the way in time — but I wonder if the lights and sirens and the panic they induce may make us overestimate their sense of urgency. In any case, studies have suggested that emergency-response teams are as likely to be help up by random traffic delays and the like as anything else.
But the larger issue is risk. As Reason magazine has pointed out, the risk of dying in a fire in the U.S. is roughly the same as drowning: In one year, 1 in 88,000, and, over a lifetime, 1 in 1100. The risk of dying in a car crash, according to the article, is 1 out of 6500 in a year. The risk of being killed while being a pedestrian? “A one-year risk of one in 48,500 and a lifetime risk of one in 625.”
Designing roads to meet some supposed emergency response criteria, for that dramatic last-second rescue, actually helps raise the risk of dying in a much more common way: In traffic.
This entry was posted on Tuesday, October 21st, 2008 at 8:41 am and is filed under Cities, Drivers, Pedestrians, Risk, Roads, Traffic Engineering, Uncategorized. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.