Anyone who rides can tell you that one of the most annoying things about being a motorcyclist is the fact that most bikes (with the exception of those with very large motors, mainly big cruiser, Goldwings, etc.) fail to trip the sensors that are placed at traffic lights to detect the presence of a vehicle waiting. Thus when you pull up to a red light, unless there is a car stopped above the sensor in the lane next to you, or one pulls up atop the sensor behind you, you may be left waiting while the light cycles through without giving you a green.
There are a lot of misconceptions out there about how the sensors (whose location is usually obvious due to a clear rectangular or octogonal marking in the pavement) at traffic lights are activated – many motorcyclists believe they sense a vehicle’s weight, and I’ve seen quite a few riders braking very heavily (almost doing a stoppie) onto the pad in an attempt to put all their bike’s weight on the front wheel, and thereby trigger the sensor. However, when you consider the location of the sensors, which is almost always directly in the center of the lane, it becomes obvious that they are not weight-sensitive – a car pulling up to the light would be straddling the sensor, with none of its wheels directly pressing down onto the plate.
After doing a little research, I discovered that most modern traffic signal sensors actually use what is called an “inductive loop”. To give a simplified explanation (for more detail, check out the article on Howstuffworks.com), the inductive loop is a coil of wire embedded in the ground at the intersection(the area of the sensor). When no vehicle is present, the coil of wire has a certain level of ‘inductance’. The presence of a large mass of magnetic metal (iron, steel) in close proximity to the coil changes the level of inductance in a measurable way, thus triggering the sensor.
The problem is, creating a measurable change requires a certain amount of magnetic metal, and the farther away from the ground the metal sits, the more mass is required. This means that not only can motorcycles have problems, but so can lifted trucks/SUVs (their engines/chassis may sit too far away to affect the inductive loop), or vehicles that are constructed mainly from non-magnetic materials, such as aluminum (an increasingly common situation these days).
Looking around the internet, several solutions are commonly suggested, any of which may be merely “urban myths”. One common suggestion is that the rider, after positioning his motorcycle so the engine sits directly above the sensor, raise the revs of the motor fairly significantly (to, say, 6k rpm on a high-revving sportbike) and hold them steady at that point. Some suggest that the more rapidly spinning crankshaft produces a magnetic field that can trigger the sensor, while others say that spinning the bike’s charging system faster produces a greater electrical charge, again affecting the sensor. Another alleged solution involves turning off the bike’s engine and then restarting it, suggesting that the jump in electrical activity from the starter will trigger the sensor.
A quick Google search also turns up numerous products claimed to consistently trigger traffic light sensors when installed on your motorcycle. Most of these appear to be nothing more than magnets or chunks of iron that are attached to the underside of the motorcycle’s frame, and we have no personal experience with their effectiveness. These devices seem to be very reasonably priced, however, and if they are effective they would quickly pay for themselves in time and aggravation saved while riding.
Short of the entire country suddenly deciding to tear up the sensors at every light and replace them with units that can detect motorcycles (which seems about as likely as Valentino Rossi retiring from MotoGP to race NASCAR), motorcyclists have two choices: continue to accept this problem, or discover which of the above solutions is effective, and employ it. We have two seperate requests for feedback: first, I ask that any readers more familiar with the characteristics and function of an inductive loop sensor (electical engineers, etc.) e-mail me with their expert opinion as to whether the ‘homebrew’ methods described above (revving the engine, turning the bike off and restarting it) actually have any effect. Second, I would ask readers who have purchased and employed any of the various products marketed as being able to trigger the sensor at traffic lights to likewise e-mail me with their feedback on the product they purchased: how much did you pay, how difficult/time consuming was the installation, how heavy was the product and how much space did it occupy, and did it actually make a difference in how many traffic signals sensed the presence of your motorcycle? A selection of responses will be used in an upcoming “reader’s response” article.
