The county where I live has installed traffic cameras that take photos of cars doing at least 10 miles over the speed limit. The county sends tickets to the owner of the car.

Somewhat controversial (though not to me), the cameras have nevertheless greatly reduced speeding in the areas where they stand. My biggest problem is that people are afraid of the camera on Montgomery Village Avenue (the main drag in my neighborhood) and slow to less than the post limit.

All the more intriguing, then, is this report in today’s Washington Post. A couple in Silver Spring, Maryland, received a ticket after a camera decided they’d been doing 100 miles an hour in a 30 mph zone.

As the Post’s Dr. Gridlock (Robert Thomson) put it,

[M]aybe if we had a video… we would watch Mr. Brennan…spin the slicks when the light turned green… aim his four cylinder tin can up the grade, wind around the two big curves in time to hit the century mark after three-tenths of a mile, then, after a tenth more, decelerate in time to make the 90-degree turn at Dale Drive.

It turns out that 68-year-old Brennan was not in fact doing 100 miles an hour during rush hour. The speed camera system is “designed to catch its own mistakes.”

Sounds good so far — but when the camera detects some glitch in its processing, it warns the humans who review its activity “by citing a weird speed to get their attention, such as 0 mph or 100 mph.”

Uh huh.

Can’t you just picture the meeting that chose this? Three engineers, a project manager, and a guy from the speed-camera marketing department. The project’s a week behind schedule, the page-by-page spec review is only halfway done, everybody’s coffee has gone cold.

Open item 372, the error routine. Well, of course anybody would see that a speed of zero, or of 100, would indicate a glitch. That simply makes sense.

I’m no engineer and I’m no programmer. I’m just a guy who’s worked a lot with the front line of organizations, the places where systems meet the outside world. I wonder why the glitch-detection routine couldn’t flag the errors a little more clearly — say, with the word glitch. Or, my wife’s off-the-wall idea: error.

I don’t know the real causes of the decision, but I can’t help thinking about a gap between the designers of the system (programmers and engineers) and the people who use it (cops and civilian employees of the police department). Imagine spending a few hours every day reviewing the output of the camera. (Here’s what the citizen receives as a citation, though my money is on the reviewer getting a nice, repetitive printout, line by line of date / time / camera / alleged speed.)

Part of performance design is making it easy for people to get clear signals. Think of the mythology around the the little gas-pump icon on your dashboard. The notion is that you fill your car on the same side as the hose appears on the icon. Great idea — except I can prove it’s not true by sitting in my own car.

Granted, that’s the hard-to-find Honda Civic, but still…

You’d think that at some point in the last 50 years, auto engineers would have thought, “sometimes people drive cars that aren’t their own, and sometimes they need to get gas.” But I suppose to an engineer it’s more logical to examine the car from the outside first, rather than foolishly getting in and driving off.

Speed limit sign probably by the Montgomery Village Foundation.
Spock photo by who knows?
Gas gauge photo by rastrus.