The rule, in one paragraph
Washington law (RCW 46.61.184) covers a bicycle, moped, or street legal motorcycle at an intersection where the signal runs on a vehicle detection device that cannot detect you because of the size or composition of your vehicle. You must come to a full and complete stop. If the signal fails to operate after one cycle, you may then, after exercising due care, proceed straight through the intersection or turn left.
Two details do most of the work here. The stop has to be complete, not a roll. And you have to give the light one whole cycle to do its job before you decide it is not going to.
Why the light cannot see you in the first place
Most demand-actuated signals in Washington use an induction loop, a wire loop cut into the pavement that senses the metal mass sitting on top of it. A car has plenty of mass. A motorcycle, and especially a bicycle, often does not disturb the field enough to register. As far as the signal controller is concerned, the lane is empty, so it never calls your green.
This is also why riders sometimes get a green on the second try after shifting position. The loop is usually most sensitive along its cut lines rather than in the middle of the lane, so the saw marks in the pavement are worth looking for.
How to actually use it on the road
Before you rely on the law, try to get the light to work normally. It usually does.
- Look for the rectangle or circle of sealant in the pavement. Stop with your wheels on one of the cut lines rather than in the open middle.
- Put your feet down and stay put through a full cycle. Watch the cross traffic get its green and lose it again. That is one cycle.
- If your light stayed red through all of that, the detector is not seeing you.
- Check that every direction is clear, then proceed straight or turn left. Due care is the standard, and it is on you.
If a car pulls up behind you, the simplest fix is to wave it forward next to you or let it trigger the loop. Its mass will call the green for both of you.
What the law does not do
It is a narrow rule and it is worth knowing the edges.
- It does not apply when the signal is working. A long light is not a dead light.
- It does not cover right turns, because a right turn on red after a complete stop is already allowed under separate law unless a sign prohibits it.
- It does not give you the right of way. Cross traffic still has a green, and you are proceeding against a red. If something goes wrong, due care is what you will be measured against.
- It does not cover cars or trucks. Those trip the loop, so the situation does not arise.
Riders sometimes ask whether an officer has to agree that the detector was broken. In practice this is a judgment call at the roadside, which is the strongest argument for waiting the full cycle and being obviously deliberate about it rather than treating a red as optional.
Where this fits in your training
Dead detectors are exactly the kind of thing that rattles a newer rider, because the instinct is either to sit there indefinitely or to dart through. Neither is good. The useful skill is the calm read: stop properly, count the cycle, check every direction, then move with intent.
That habit gets built on a range before it gets tested at a real intersection. Our beginner permit course puts you on a training motorcycle with an instructor watching, and the endorsement path covers the street strategy behind rules like this one. If you already ride and want the road craft sharpened, the advanced course is built for that.