Grooving In

After posting about the traffic light trip switches on MLK street yesterday, I got an e-mail from a reader asking me what I was talking about. "Please 'splain," they asked.

Just behind the stop line, there are thin grooves cut into the pavement with copper wires buried in them, and covered with either tar or rubber. These wires form loops which are fed electricity to produce a magnetic field. When a car is in that magnetic field, they can sense the change it produces in the magnetic field. When that happens, the traffic light is "tripped."

If you look for them, you'll soon learn which ones are "tripped" and which ones simply run on timers. Worcester's intersections have an abundance of trip-switch controlled traffic lights.

This is why it's worth noting that they paint "stop lines" at most intersections. They're painted on the street to let people know exactly where they should stop if it's a trip-switch controlled traffic light. If you stop way before the stop line, or go beyond the stop line, then your car may not trip the switch.

Here, for example, is a car I came upon while scouting around for pictures on this subject. They had been sitting there waiting for the left turn signal to change for much longer than it would take for the trip switch to work. I only had a couple of seconds to take the picture, because I know this trip switch changes the light in a very short time, and I had tripped it when I pulled up behind them.

A notable spot where people seem to think they paint those lines in the road for decoration is in front of the DCU, outbound on Foster.

I can't count the number of times I've driven past there and seen some space shot sitting there waiting to take a left, but they're way past the stop line.

This trip switch takes a long time, too, so the wait is long at that spot to begin with. It'll take forever, though, if you're the only one there and you've gone past the stop line.