What do those bike symbols mean?

Safety Corner logo

 

by John Allen

 


Near the end of the Lexington Revolutions ride on July 4, I came up on several ride participants waiting in line for a red light. I entered a left-turn lane, to head for the popular yearly post-ride party at the home of Bill and Sheila Widnall. There was a small bike symbol painted on the road under my wheels, and between the other cyclists and me, another such symbol in the middle of the right-hand travel lane. Why?

As we waited, I asked the other cyclists why they were all at the extreme right edge of the roadway, considering that the bike symbol indicates the “sweet spot” of a metal detector that triggers the traffic light.

One cyclist appeared to have heard about this before, and explained that he had an aluminum bike, so the sensor would not work!
Actually it probably would work—Massachusetts uses loops of wire buried in the road surface—metal detectors, not magnetic detectors—and, if they are correctly adjusted, the hoop of metal in a bicycle rim is enough to trigger them. A pack of eight or ten bicyclists would almost certainly trigger a detector.

A car stopped at the opposite side of the intersection. Soon after, the light changed (I’m not sure who triggered the signal) , and we all went on our way.

If you ride the same route time after time, you will come to know the detectors and how well they work. Usually, you can identify them by a pattern of saw cuts in the road surface, where the sensing wires are buried. The older detectors are simple rectangles, and you can sometimes trigger one of these by riding along its edge. The newer, better detectors have third saw cut in the middle of the lane, halfway in between the other two. That is the most sensitive location and that is why the bicycle marking is in the middle of the lane. If a street is newly paved, you may only see the bicycle marking—and let’s hope there is one!

Do you need to wait in the middle of the lane? Well, you only need to trigger the detector if there’s no other vehicle to do that, and in any case, first come, first served is the rule at traffic lights. Lining up in the middle of the lane at an intersection also discourages the “right hook collision”, where a motorist comes up from behind and turns right across your line of travel.

Increasingly, video detectors are coming into use—you can sometimes spot small cameras mounted on overhead traffic-signal masts, pointed toward where the first vehicle waits at the light. These detectors usually work, but at night you may have to shine a bicycle headlight directly at the camera.

If a detector does not work, you have three choices:
• Wait for another vehicle to show up and trigger it—which could be a long wait especially when you are on a lightly-traveled street that crosses a major street;
• Stop cross traffic by pushing a button for a pedestrian signal, if there is one—requiring you to leave the road and become a pedestrian. The pedestrian signal holds the signal long enough for a pedestrian to cross, adding delay for waiting motorists.
• Cautiously proceed on the red light—which can give bicyclists a bad reputation and also can be dangerous.

None of these is a good choice. If a detector doesn’t work, it’s appropriate to discuss the problem with your city or town traffic department. Bicyclists are legal traffic, and the signals should work for us, too. Please do your part to help correct defective detectors.

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