Can Cyclist Get a Signal Change?

It’s happened to every cyclist. You roll up to a red light to cross a major road, wait for the light to change, and... nothing. A car rolls up behind you and... voila, the signal changes! It’s moments like these where you’re reminded that so many of our streets weren’t exactly built with cycling in mind.

Thankfully, there are a few strategies – beyond simply rolling through the light – that can help you overcome this. 

First, let's review the basics.

Most controlled intersections (those that use traffic lights, for instance) in Arlington use some form of traffic detection that helps determine when the lights will cycle. Arlington’s major roads time their signals through an adaptive control system that responds to increases and decreases in traffic flow over a day. Changes in these signals don’t depend upon the presence of any one vehicle, and will simply run through the light cycle on a schedule. In other words, there’s nothing a cyclist can do to affect the light signal while travelling along a major road like Lee Highway.

In contrast, traffic signals on smaller roads – including those that cross major roads – are often only triggered by the presence of traffic. In Arlington, there are two methods of detecting traffic in these cases. The method that’s been around longest is the detector loop. Also referred to as an induction loop, it is triggered when a car or bike disturbs the magnetic field created by the loop.

You can recognize detector loops by the cuts in the pavement near the intersections. They’re usually in the form of a square, though there are other patterns. The trick is to place the bicycle’s wheels directly over the pavement cut parallel to your direction of travel. This should provide enough of a disturbance to trigger the signal. Contrary to popular lore, a bike or wheel need not be made of steel for this to work. It must simply have some kind of electrically conductive metal.

The other method of detecting traffic in Arlington involves video detectors. They are increasingly replacing loop detectors as the county repaves its roads. These detectors look like video cameras attached to small poles extending from the larger traffic signal poles. They don’t actually relay video anywhere, but rather trigger a signal change when it recognizes that a car or bike is waiting in the road. This recognition is managed via an algorithm involving a change in pixels as compared between the scene with an empty street and one with a car or bike waiting in the road.

Since the video detector isn’t dependent upon the cyclist knowing that he or she should place their wheel over the pavement cut, it’s generally superior to a loop detector. However, some video detectors in Arlington are poorly aimed or obscured by trees. In that case, there are a few solutions. The cyclists can stop within the actual view of the detector or simply avail themselves of the benefits of Virginia Code 46.2-833. The third option is... well, it’s probably the most popular option.

If more cyclists were aware of how to trigger traffic signals, and Arlington worked a bit harder to make sure its detectors always recognized cyclists, we could make that third option a bit less popular. Be safe out there, and wait for the green.

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What's that Virginia Code link about? Virginia law now permits cyclists to legally proceed through red lights under certain conditions. More here.

Want to know more about how detector loops work? There's a good explanation here, along with some good tips on safe lane positioning.

Mark Blacknell is chair of the Arlington Bicycle Advisory Committee, president of the Washington Area Bicyclist Association, and a League Cycling Instructor.