Via the St. Petersburg Times comes an interesting discussion of highway design featuring an old bugaboo, exiting on the left. In Traffic I spoke with some people at the FHWA who mentioned, essentially, that contemporary highway design tries to avoid exiting on the left, for a variety of reasons, including driver expectancy.

The piece brings up a number of issues. For one, it notes that three people have died on this section of highway, including one last week. No figures are given before that, though the facility opened in 1978. So whether this is an epidemic, or merely random, is hard to say; there may be a “regression to the mean” and we won’t see any further fatalities for the next ten years.

Second, and always lurking, is the issue of “driver behavior.” The most recent fatality, the article notes, was traveling 93 MPH. Is there a social responsibility for protecting someone behaving that negligently? If he had died by striking another vehicle, we wouldn’t be talking about bad design. Further, can good design save everybody (and what would the cost be)? I’d say we should be more worried, socially, about the harm that person may cause to others (and keeping those people off the road). The German autobahn was and is considered a design marvel; its smooth tarmac has also been home to many spectacular deaths.

The piece notes: “The left exit is counterintuitive, forcing drivers to slow down in the fast lane. The road’s elevation occludes a clear view of what lies around the corner. And the short, angled barrier walls do little to keep vehicles on the road, he said.”

Well, technically, people, there’s no such thing as a “fast lane.” There’s a passing lane. There’s also a speed limit. I also note a sign that clearly marks a reduction in speed on the ramp. And this isn’t really the sort of left-hand exit that people normally talk about giving drivers’ trouble — this is really the majority of the highway quite clearly swooping up and off to the left.

That said, the state engineers may be a bit too blithe in dismissing the risk. As a casual observer, I can imagine any number of small tweaks that could be done here relatively cheaply (cheaper than raising the height of the concrete walls). Rumble strips, flashing lights on the signs, etc. But I wouldn’t say this warrants some expensive overhaul — where’s the money coming from, anyway? — due to the actions of some severely negligent drivers.

(Horn honk to Shirl)

This entry was posted on Friday, March 6th, 2009 at 11:39 am and is filed under Traffic Engineering, Traffic safety. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.