Why Motorcycles Get Stuck at Traffic Lights The Shop Manual
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00:00We've all been there.
00:07You pull up to a red light at an empty intersection or freeway on-ramp, and you wait.
00:15And wait.
00:16And the light refuses to turn green.
00:20You're basically trapped there, hoping a car will pull up next to or behind you and
00:25finally trip the traffic light.
00:28So why is it that motorcyclists have such a hard time at signals?
00:33And more importantly, what can you do about it?
00:38Let's open up the Shop Manual and find out.
00:50This episode of the Shop Manual is brought to you by Kershaw, my go-to unboxing knife
00:54and a tool I carry with me everywhere.
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01:04Some traffic lights work on timers with set schedules, while some more modern intersections
01:09might use video surveillance or even radar.
01:11However, the majority of intersections rely on sensors in the ground to detect traffic
01:16and trip the light.
01:18Take a look at just about any intersection, and you'll likely see circles or squares
01:22cut in the pavement a few feet back from the stop line.
01:26Those tar-filled traces are from the installation of inductive loop detectors, which were introduced
01:30in the 1960s and are what the majority of intersections use to tell if a vehicle is
01:35present.
01:37Contrary to urban myth, the detectors do not rely on pressure sensors that weigh vehicles
01:42at the intersection, and there are no permanent magnets in the ground that interact with the
01:45iron and steel in a vehicle's engine and chassis.
01:49Magnetism, or more accurately electromagnetism, does have something to do with it, though.
01:54What's down there in the ground is just 2-3 loops of wire, usually 12-16 gauge stranded
02:00copper stuff just like the wires that power your bike's headlight.
02:04Except in the ground, they're carrying alternating current at a frequency of 20-30 kHz.
02:10And as per some 19th century scientists by the name of Faraday and Lenz, current flowing
02:15through a coil creates a magnetic field, which in turn induces current and a separate magnetic
02:20field in any conductive material that's nearby.
02:24What this means is that when a vehicle stops at an intersection, the loop's electromagnetic
02:28field imparts a current in the car, which in turn induces a magnetic field in the car,
02:33which affects the frequency of the current in the coil.
02:36The controller in a nearby cabinet registers that change in frequency and recognizes that
02:41a vehicle is waiting at the signal.
02:44It's a bit of a tail-wagging-the-dog-wagging-the-tail scenario, but ultimately, inductive loop detectors
02:50are a good solution, because they work with any conductive material, like aluminum, rather
02:55than relying on ferromagnetic materials like iron and steel.
02:58However, the size of the conductive mass and its distance from the ground play a big role
03:03in detection, so while cars and trucks and some lower, larger motorcycles like road glides
03:09and gold wings don't have issues, smaller and taller bikes do, which can leave you waiting.
03:15Luckily, every loop sensor has a sweet spot, so you can usually get the green by simply
03:20stopping in the right location.
03:23For standard circular and square detectors, called dipole loops, sensitivity is higher
03:27along the perimeter, and it's highest where the lead-in wire joins the loop.
03:32Park over that, with as much of your bike over the edge of a round loop or along the
03:36straight run of a rectangular loop, and you'll increase your chances of tripping the sensor.
03:41However, positioning yourself like this may place you closer to moving traffic in adjacent
03:45lanes, or force you to put a boot down in the center of the lane, which could be slick
03:49with leaked oil or coolant, so be careful.
03:52If the outlines look like two narrow rectangles pressed together, or if there are diagonal
03:57saw cuts across the interior of the loop, it's a quadrupole detector, and you're best
04:01off stopping right in the middle.
04:04If optimizing your bike placement doesn't do the trick, you may need to wave to the
04:07car behind you so they pull forward over the loop sensor.
04:11Or if there's no other vehicle around to help you out, you might revert to some age-old
04:15light tripping technique like putting your side stand down on the cut line, which I will
04:20admit I've had some luck with.
04:22Or some people swear by revving their engines to spin the charging system faster, while
04:27others say that cycling the starter will do the trick.
04:30Both strategies do produce an intense magnetic field, but in practice it's too small and
04:35too far away to reliably affect the sensor.
04:38Plus, shutting your engine off at an intersection would make me feel vulnerable, and revving
04:43your bike at a red light is kind of obnoxious.
04:47Then you've likely heard about some device or accessory that is guaranteed to trigger
04:50a green light.
04:52All the gadgets I've seen are just powerful permanent magnets that you stick to the bottom
04:55of your bike.
04:57And similar to revving your engine or cycling the starter, the idea is that the magnetic
05:00field will trip the detector in the ground.
05:03Unfortunately, I haven't found these to work reliably either.
05:07I even called and emailed the company to discuss its claims, but they never got back to me.
05:11So green light gadgets, at least in my experience, aren't a solution.
05:17In the end, if the light refuses to change for you, you could just run it.
05:21Seriously, depending on where you live, it might be allowed.
05:25There are currently 12 states, including Arkansas, Idaho, Illinois, Minnesota, Missouri, Nevada,
05:31North Carolina, Oklahoma, South Carolina, Tennessee, Virginia, and Wisconsin that have
05:36so-called dead red laws that allow motorcyclists to proceed on a red light.
05:41These laws vary by state, so make sure you know the specifics before utilizing them.
05:46But if you're like me and you live in a state where the power of the red light is almighty
05:50and you are never allowed to proceed, then your options are careful lane placement, which
05:56will probably help, or some engine-revving, magnet-applying, salt-over-the-shoulder trickery
06:01that may or may not contribute to the light turning green.
06:05Or if you want to take matters into your own hands and solve the problem for yourself and
06:09everyone who rides that route, call your city or town's Department of Public Works and report
06:14the problem.
06:15The sensitivity of inductive loop detectors is adjustable, and there are people whose
06:19job it is to make sure that traffic signals work for all vehicles, including motorcycles.