Join Date: Nov 2005
Location: Eugene, Oregon,
I done some research on this issue a couple of years ago and the following is what I came up with.
Be seen by traffic sensors
Many riders are often frustrated by traffic light sensors that fail to detect the presence of a motorcycle. TEAM OREGON instructor Patrick Fitzharris recently contacted Mark Rodgers, the manager of the Traffic Signal Services Unit of ODOT. Rodgers offered some insight into how vehicle sensors work and how riders can help themselves be more "sensor visible." Here is an excerpt of Rodger's response:
As a fellow motorcyclist, I understand the frustration of not getting detected by the traffic signal when I am riding my bike. Please allow me this short lesson to show how a traffic signal senses motor vehicles. Hopefully you can better exploit the sensors by understanding how they work.
A vehicle sensor, typically referred to as a "loop", is simply a coil of
wire embedded into the road surface. An electronic module in the traffic signal control cabinet sends a signal to the loop, which causes it to behave as a metal detector. Any mass of metal that passes over the loop causes a shift in the electrical signal. When the shift is great enough, the module tells the computer that a vehicle is present. The key point here is that the mass of metal must be large enough to overcome a threshold, or minimum metal mass. All metal objects greater than the threshold will be detected.
One other factor of the loop is called geometry. Oregon uses one of two loop configurations, a round loop and a diamond shaped loop. Invisible lines of magnetic force form at right angles to the wire. Maximum sensitivity results from metal masses moving perpendicular to the lines of force, so that as many lines are cut through as possible. In either type of loop, this zone lies about halfway between the center line of the loop and the left or right edge of the loop. If you stop over a loop, I recommend that you place your bike so that the lowest part of the frame is directly over the wire. Do not stop in the middle of the loop, as there is a dead zone inthe middle.