Bicycle signal detection on Soapstone Dr bike lanes

Randy and David check detector location and sensitivity.

The Soapstone Drive road diet project is nearly finished. Approximately two miles of bike lanes were created when four travel lanes were reduced to two regular travel lanes, bike lanes, and a center turn lane. The bike lanes are striped and a few bike symbols have been painted in the lanes, with several more to be added before the project is complete.

There are three traffic signals within or adjacent to the project, at Lawyers Rd, South Lakes Dr, and Sunrise Valley Dr. At most traffic signals in the county the presence of motor vehicles is detected automatically. As many cyclists know, they don't always detect bicycles. BikeLoudoun asked VDOT about this issue last year and wrote the response in their blog post Why Doesn't the Light Turn Green for Bicyclists?

According to VDOT Regional Operations Maintenance Manager, Mark D. Hagan, "most of our traffic signals in Northern Virginia use what are known as 'inductive loops,' which is a loop of wire located within the pavement with a small electrical charge that creates an electrical field. The electronic device within the control box cabinet looks for an inductance change within that electrical field and triggers a signal that a car, motorcycle or bike is present."

Detectors have been placed in the bike lanes on either side of the traffic signal at Soapstone Dr. and South Lakes Dr. On Saturday VDOT traffic engineer Randy Dittberner and a signal technician from VDOT met David Gibson of Federal Highway Administration to determine the location and sensitivity of the detectors.

The detectors are embedded in the pavement and there's no sign of them on the surface. Thy are located about 5 feet behind the bike lane stop bar. When the bicycle passes over the sensor it is detected and a call is issued for a signal change. However, if 10 seconds passes before the signal changes, the call terminates. In order to ensure the light changes, cyclists need to stop on the sensor. Since the sensor isn't visible, a marking is needed to notify cyclists where to stop.

The Bicycle Detector Pavement Marking is used for this purpose: "A symbol (see Figure 9C-7) may be placed on the pavement indicating the optimum position for a bicyclist to actuate the signal." In the photo above, the bike symbol will be located where the letters "BK" are painted.

To our knowledge, these are the first bike detector markings used in the county. This is progress. Look for them the next time you're riding along Soapstone Dr.