Biggest Little City

Traffic Signal Vehicle Detection

In order to move traffic efficiently, vehicle detection is a means of telling the device that controls the red, yellow and green lights, when a car is present. Inductive loops are the most common type of vehicle detection in use today, although video is fast becoming popular.

Inductive Loop
Movement and weight are not required for detection! The vehicle detector has two parts, the inductive loop itself installed into the roadway surface and the amplifier mounted in the signal control cabinet. The inductive loop is attached to the amplifier in the cabinet through a series of wires and cables. The amplifier monitors the frequency constantly and if it sees the frequency "change" then it knows that a vehicle has entered the detection area and sends a signal to the traffic control device. The traffic control device can then respond as programmed, usually changing the assignment of right of way (giving a green light) to the direction with the vehicle in the detection area.

Video Detection
Video detection is relatively new. The technology is very sophisticated and uses artificial intelligence developed for use in weapons such as smart bombs and cruise missiles. A video camera inputs its image into a processor which "learns" what the image looks like.

Video is extremely flexible and easy to change unlike an inductive loop installation.

Frequently Asked Questions
Do all signals have vehicle detection?
No they do not. In the downtown core area the distances between signals are small and traffic volumes are relatively fixed so vehicle detection was not installed. Virtually all other signals outside of downtown are "actuated" or have vehicle detection.

Is vehicle detection "on" all the time?
Yes, however as a driver you may not immediately see a green light. Depending on the time of day and what road you are on, the road may be part of the coordinated signal system in which case the central control computer may "hold" a main street green in anticipation of a group of cars arriving shortly from a neighboring signal. This is common on streets such as Kietzke, Virginia, Mill, Keystone, McCarran, Wells, Plumb, and Oddie.

What happens when a vehicle detector "fails"?
The amplifier will send a constant "request for service" or "call" to the traffic control device. This will turn a side street green even if there are no cars there and hold it green for the maximum allowable time that it is programmed to be green in the traffic control device.

What are the major causes of detector failure?
The biggest single cause of detector failure is construction. Construction of a new building usually involves new sidewalk and cuts in the roadway to connect sewer and power. Whenever utility work must be done, usually the roadway is cut with a concrete saw. This cuts the loops installed in the roadway and renders them useless.

Secondarily, the roadway itself will wear out, and create cracks or pot holes which expose the loop wires. Traffic running over them renders them inoperative.

How come the detector won't pick up my motorcycle?
With very small vehicles such as a mo-ped or some motorcycles, the detector may not be sensitive enough to pick it up. Most cyclists do not notice a problem during the day as there are enough regular cars to actuate the loops. The problem becomes very apparent at lightly used intersections or in the early am or evening. Make sure you are stopping in the correct location, that is behind the white line or crosswalk. The most sensitive areas of detection are to either side of the lane, not in the middle. Machines made mostly of alloys or aluminum that are high off the pavement will be more difficult to detect. While signal staff has not verified it by experiment we have been told by police officers that installing a small loop of wire with several turns (go around in a circle two or three times) about nine inches to a foot in diameter under the frame of the motorcycle parallel to the roadway surface will make the detector work every time.

Who do we call if we suspect a detector problem?
Please call 775-334-2256 between 7:00 am and 3:30 pm or 775-334-2456 for the answering machine after hours. Please leave your name and number and as detailed a description of the problem as possible. Alternately you may contact Reno Direct.

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