Bicycle Loop Detectors

WSBC heard that some people don’t know that the Seattle Department of Transportation (SDOT) added bicycle loop detector markings at many intersections. These markings indicate where cyclists should stop in order to trigger a green light at a signalized intersection.

The marks can be seen as one pulls up to a red light, so as long as there are no motor vehicles in front of you. The marker will generally be located behind the white stop line and generally slightly to the right, positioned over the vehicle sensor that’s embedded in the pavement. There are two forms we see most regularly; the older “T” marking or the newer small “bicyclist” marking, seen here.


Simply make sure your front tire, at least, is centered over this white marker and you should be added to the signal rotation.


Some intersections don’t have this marker, or they may be faded away. If you think a specific intersection should have a marker but doesn’t you can contact and let them know.

Some intersection signal phases are triggered by camera, not a pavement marker, and these are trickier to identify. If you are not picked up when using a loop detector marker, the light skips you on a regular basis, takes an inordinate amount of time to change, or you need more information, you can contact SDOT at the email address above. Reporting signalized intersections that don’t pick up waiting cyclists should be fixed quickly to help prevent impatient red-light running and general cyclist frustration.