I enjoyed this post from Jeff Sommar on the ambiguity inherent in “Speed Zone Ahead” and other road signs. About “Speed Zone,” he writes: “Reading it at face value, which when you think about it, is how street signs should be read, you would think that the sign is alerting you to the fact that you will be able to speed up in the zone ahead.”

He goes on to mention the sign is used to signal increased speed ahead, as well as decreased speed, which I don’t think is actually true (please confirm, any engineers). But his point about the vagueness is well taken. The sign, after all, doesn’t tell you how much the speed is dropping by (or exactly when). As it turns out, the engineers have heard his cry of confusion, and the sign as pictured above is on the way out, according to some chatter on the MUTCD websites (this site shows some of the new configurations, which are yellow rather than white, and state specific decreases — never increases — in speed). As a side note, there’s also some discussion about what the proper placement is of these signs — so drivers have sufficient time to react and slow before hitting a new speed zone and, perhaps, a speed trap.

The “Speed Zone Ahead” sign brings up another issue of mine, which is the problem of having a road marked for, say, 65 mph, which suddenly hits a stretch that is 35 mph — but the road is exactly the same. The “Speed Zone Ahead” sign is thus a rather weak signal in changing behavior. I think compliance would be higher if, for example, the road were made narrower in the slower section; some alternative paving treatments were introduced; another potential solution is “optical speed zones,” the subject of an article in the latest ITE Journal by Steven Latoski — this treatment uses “bars” painted across the road that diminish in proximity as the driver progresses across them, thus increasing the feeling of speed, thus targeting “an instinctive road user reaction of relaxing the accelerator or adjusting the cruise control.”

I also like Jeff’s mention of the “Dangerous Intersection” sign. Given that signalized intersections account for a very high percentage of traffic crashes, perhaps this should be placed at all intersections. I understand the impulse to put up the sign, at least to provide liability coverage; but is that really all that can be done? And does putting the sign up at one location cause one to lower one’s guard at other areas not so marked? Tricky stuff, this traffic engineering.

Anyone else have favorite examples of signs that gave them pause? My favorite is one that says, simply, “No Traffic Signs.”

This entry was posted on Sunday, March 29th, 2009 at 6:41 pm and is filed under Drivers, Traffic Engineering, Traffic Signs, Traffic Wonkery, 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.