Granite Geek: Should Motorcycles Get A Green Light To Move Through Some Red Lights?

Dec 30, 2014

Some stoplights sense cars and trucks and change signals when they show up. Motorcycles, not so much.
Credit Katie McColgan via Flickr/CC - http://ow.ly/GC9F0

These days many stoplights will start changing to green when the intersection detects a car or truck. But some of these intersections don't detect motorcycles, at least not regularly. And a bill before New Hampshire's legislature would let those otherwise stuck bikers ride on through red lights.

David Brooks writes the weekly Granite Geek science column for the Nashua Telegraph and GraniteGeek.org, and he’s been scoping out this issue. He joined All Things Considered with some of what he’s learned. 

To start, how do stoplights detect when a vehicle is there? I always thought you just drove over some kind of pressure plate and it detected the weight of the car.

Many people think that, including me in my younger days. In fact, if you study this issue a bit, you'll find people laughing about seeing folks on motorcycles bouncing up and down, because they think they're trying to make the pressure point work.

An individual stoplight knows [because] there's an inductive loop put in the pavement - it's a couple inches deep and pavement's put over it. And it detects the passage of either magnets or large pieces of moving metal overhead, because there is an inductive loop happening, electricity happening through the loop at all times, which creates a magnetic field. When it's disrupted, it disrupts the electric pattern and that, in turn, sends a signal to the light which says, hey, there's somebody there, so change.

The problem is that these things are set for a certain amount of metal to pass overhead, like in a little tiny car or anything bigger than that. A motorcycle may not have enough metal in it - it certainly doesn't have enough of a magnetic field in it - to trigger them itself. This is particularly the case in recent years because some motorcycles now use aluminum frames because they're lighter, and they're non-ferrous, non-magnetic metals, and that really won't trigger it.

What do riders do to avoid getting stuck in place forever?

There are a number of things you can get, the simplest of which is to attach a metal plate to the bottom of your bike somewhere, just to increase the amount of metal that will go through and disrupt the pattern of the inductive loop.

There's a battery-operated loop that you're supposed to be able to attach to your bicycle frame that will generate a magnetic field, and other things like that. So obviously this is a big issue. And there are a couple of states that have passed laws already which would allow motorcycles to run the red light in this circumstance. And that's what has been proposed by a Nashua state representative named Don Lebrun.

It basically takes the state law about turning right on red and says, if you're a two-wheel motorized vehicle including scooters or motorcycles, and it's safe, and you've waited long enough, then you can also go straight on red or even turn left on red.

Now I read you came up with a different solution of sorts as a kid when you created a comic book supervillain?

Yes - the best one was the Red Light Baron, who had the power to change stoplights at will.

Try getting the Batmobile out to chase supervillains if you're stuck at every single red light in Gotham City.

If this law passed, the Red Light Baron would not be able to halt the Bat-cycle, although he would be able to halt the Batmobile.