Traffic Signals

Green means go. What more is there to know?

Even most children know what red, green and yellow lights mean. There’s more to learn about traffic signals that that.

What kind of traffic signal presents the greatest risk for left-cross crashes? How does signal detection work, and how do we make use of it as bicyclists? This video will answer those questions, and more.


Topic 12: Traffic Signals & Detection

Topic Introduction

Even most children know what red, green and yellow lights mean. We know that lights are solid balls or arrows — and some have bicycles on them (but we’ll talk about that in the next lesson).

Signal Phases

First, let’s talk about yellow lights.

Even fast bicyclists are often much slower than motor traffic, especially on suburban roads. We don’t have the ability to mash the gas pedal and accelerate well above our cruising speed.

If a signal turns yellow just as you arrive at a large intersection, you may not have time to get across the intersection, and you don’t necessarily want to slam on your brakes.

It’s a good idea to monitor the signal to know if has been green for a long time. We call this a “stale green.” If you can anticipate that the green is stale, it’s safer to slow a bit and allow it to change before you get there.

One way to monitor the signal is to watch the crosswalk countdowns. These aren’t 100 percent reliable, since many will count down long before the light changes. But in some areas, they can give you a good idea of whether or not the green light is stale. And in some places they tell you exactly how much time you have.

The cool thing is, if you know your sprinting ability and you can make the light, you get the big bonus of having the road to yourself after the light shuts down traffic behind you!

Turn Arrows

Now let’s talk about turn phases.

A right-turn arrow, when green, offers a protected right turn while the thru traffic has a red light. This usually coincides with protected left turns for the cross street. Be aware of those drivers making U-turns, especially if you’re planning to go to the left lane.

Left-turn arrows provide a protected phase when left turns can be made while oncoming thru traffic is stopped. A protected left turn is very valuable when turning across a busy, or high-speed, road.

Protected left-turn signals can restrict left turns to only the green arrow, or they can have a permissive phase when drivers can turn left after yielding to oncoming traffic.

When you are the oncoming traffic, it’s nice to know if the signal is permissive or not, so you know if a left cross is possible. Some signal heads are identifiable from the back.

Here’s what to look for:

If there is one three-light stack over each thru lane and the turn lane, there is a good chance the left turns are restricted.

If there is a stack of 5 lights over the left turn lane, these drivers have a protected phase and can turn left after yielding to thru traffic.

If there is no signal head over the left turn lane, there is a good chance left turns are not protected. Because it is harder to turn left here, drivers are more likely to bolt through a gap in oncoming traffic. Left-cross risk could be higher at these intersections.


There are some things you need to know that motorists don’t — like how to get a traffic light sensor to detect you and your bike.

Loop detectors

For a few decades, traffic engineers have been using what they call “loop detectors” to determine if a vehicle is present at an intersection, and if so, to send a signal to the controller so it knows to make the light change.

These “loops” are really just big metal detectors. They work the same way that hobbyist metal detectors do, the kind people use on the beach to search for buried treasure.

Wires are embedded in cuts in the pavement, and the current running through the wires creates a detection field. Many of these loops can detect a bicycle, but some don’t do so well.

Loops in a simple square, circle or diamond may not be able to detect your bike. You can increase your chances of detection by stopping your bike directly over one of the cuts in the pavement, or by laying your bike down horizontally over the detector. If a motorist comes up behind you, sometimes the easiest thing to do is move forward into the crosswalk and wave for the motorist to stop on the loop.

Loops with more complex shapes tend to be more sensitive. Riding over the center of such loops is usually sufficient.

In some places, markings have been put on the loops to show cyclists where to stop their bikes for detection.

Video cameras

Many places are now switching from loop detectors to video cameras for traffic detection. You’ll see them mounted on a pole or mast arm near the signal head. With these devices, a computer registers the difference between an image of an empty lane and one with a vehicle in it.

During regular daylight hours, such cameras should be able to detect you. But at night or in low-light, they may not. If you feel like you’re not being detected, shine your headlight directly at the camera.