Margin of Error

Margin of Error

What makes good infrastructure? One key feature is that it is forgiving. Infrastructure that requires expert skills and an absolute focus is crappy infrastructure.

Photo courtesy of Michael Snyder via SeattleBikeBlog.
A recent example of this can be found on the Burke-Gilman Trail. This is the grandaddy of multi-user trails in Seattle. It’s a major route for bicycle commuters during the week and is thronged with the kids & dogs crowd on the weekend. It’s one of my favourite parts of Seattle. However, it does have its flaws, including a spot near NW 41st St. where the trail crosses railway tracks. The trail does try to indicate that cyclists should cross at a 90 degree angle, but the natural path to take is a shallow angle that places cyclists at considerable risk of catching a tire on the track and falling. To try to improve safety, a rubber mat was installed. This does prevent catching a tire, but can become very slippery itself when it’s wet or frosty. Not surprisingly, this has been the site of many accidents (well covered by the Seattle Times and SeattleBikeBlog) and I’m happy to hear that SDOT is fixing it.
The response to the story has been fascinating. At some point in the comments, you’ll typically see an exchange like this:
  • People ride too fast there! I always slow down enough and cross at a 90 degree angle and I’ve NEVER had a problem
  • Well, I’m a VERY experienced cyclist and have crossed that spot thousands of times without a problem before falling and breaking my arm!
  • People have to learn how to cross railway track safely. Slow down and cross at a perfect 90 degree angle!

Now, I’m all for safety, and hearing about these accidents certainly reminds me to be careful when crossing the tracks. I also recognize that the city can’t find and correct every hazard out there, whether it’s gravel, potholes or wet leaves. However, I think people tend to miss the point. When we build and design infrastructure, we can’t assume that everyone using it will be highly skilled. We also can’t assume that those who are skilled will be paying perfect attention at every moment in time. Our brains do not work this way. We all get distracted by things we see on our way, personal issues, or even thoughts of dinner. If a spot is particularly risky, you can do everything correctly (which we often don’t) and still have a significant chance of falling.

If our infrastructure demands perfection, it’s only a matter of time before we’ll fail. Good infrastructure allows for some margin of error. We demand it in the design of our highways and cars – let’s also demand it in our bicycling infrastructure.

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