A traffic signal technician at PDOT just released a really cool document titled, “Vehicle Detection: Or, Getting a Green Light on a Bicycle at an Intersection.”
Here’s an excerpt from the, “How we mark for bicycle detection” section:
“Whenever we receive a request to mark an approach for bicycle detection, our electricians use a bicycle to test the loops. Once we verify a location where a loop consistently detects a bicycle, we paint the spot with a temporary white mark in the shape of two small arrows facing each other (see Figure 3). Then we notify the good folks in the Pavement Markings Section and they put down a permanent mark with hot plastic in the shape of a small bicycle (similar to the bike lane mark only much smaller). There are some locations where the sensitivity of the loop has deteriorated and is unable sense a bicycle. We replace those loops as time and budget permit.”
The signal technician then offers some helpful hints:
“The detection does not lock in a call at most traffic signals. Therefore, you must stay on the mark because as soon as you leave the mark the traffic signal controller will drop your call for a green light and it may take another cycle before you get served.
Also keep in mind that some traffic signals have very long cycle lengths and it may take a while to get served on a side street. Cycle lengths may be as long as one hundred and twenty seconds and although two minutes may not sound like a long time, it may seem like an eternity when waiting for a green, especially if you are impatient like me.”
Here’s the full PDF (188K) with more details for all you signal detection junkies.