Preventing collisions at intersections

I’ve seen several people writing about Tom Vanderbilt’s thought-provoking, Traffic: Why We Drive the Way We Do (and What It Says About Us) . Every few pages there is a good idea that leads you down some mental rabbit hole. I have highlighted passages and dog-eared pages on the Kindle every time I sit down to read it. The universal experience of driving has turned us all into amateur psychoanalysts navigating complex social interactions, so the book’s popularity is understandable and says a lot about how much is going on while we’re just driving.

In one chapter of the book, Vanderbilt relates some of the engineering conundrums that come into play when trying to manage intersections, specifically the amber lights that precede red stop lights. Traffic engineers have experimented with many ways to manage intersections safely, including flashing green lights prior to changing to amber, lengthening yellow lights, or including flashing signs that the light is about to change. It turns out that every method they have tried does little to reduce collisions. Drivers either adapt to lengthened amber lights and flashing green lights by taking more time to go through or they stop suddenly before they need to. Increasing the yellow light does nothing to reduce collisions while actually decreasing the capacity of the intersection.

One thing they could try is to randomly increase the delay between the red light and the crossing road’s green light. In other words, if a driver fails to cross before the light turns red, a delay on the crossing green could prevent side collisions as the crossing traffic will not receive the signal to cross until the intersection has been cleared for a second or two. You would have to randomly increase the delay so that drivers could not adapt to the delay pattern by running the red light later. Also, even though some people are willing to run red lights, fewer do so than run late yellow lights. One other thing you could do is develop the capability to increase the delay by detecting any cars crossing against the red light.

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  1. Testing disqus comments again.

  2. Testing disqus comments again.