Railroads

How does VDOT decide when and where to install traffic signals?
Those red, yellow and green traffic signal lights are vital to controlling traffic in a safe, orderly manner. They let motorists "take turns" in moving through busy intersections and can enhance safety.
But, in the wrong location, a traffic signal actually can contribute to accidents and congestion. A potential accident exists every time a vehicle is stopped on the traveled portion of a highway.

Nearly every driver has experienced the anxiety of having a light suddenly turn yellow while rapidly approaching an intersection, or getting caught behind one red light after another on a busy thoroughfare.

The Virginia Department of Transportation's job is to find the point where a signal will help more than it will hinder and relieve more congestion than it will cause. In every case, VDOT's primary consideration is the safety of the public using the intersection.

What is the purpose of a traffic signal?
Traffic signals are designed to ensure a safe and orderly flow of traffic, provide safety for pedestrians or vehicles while crossing a busy intersection, and help lessen the severity and frequency of accidents between vehicles entering intersections from different directions.

How does VDOT decide whether a traffic signal should be installed?
The department follows federal guidelines that establish minimum conditions under which a signal installation should be considered. These guidelines help identify potential locations for signals, but each location is reviewed individually before a signal is installed. Traffic engineers assess whether or not a signal is a proper means of traffic control by carefully evaluating the number of vehicles and pedestrians that use the intersection, the physical make-up of the intersection, roadside development, delays experienced by motorists during peak hours, average vehicle speeds, future road construction plans and the number and types of accidents that have occurred.

Are traffic signals a cure for accidents? 
Not in all cases. Certain types of accidents can be reduced in number or severity by the installation of a signal, while other types may not be affected. VDOT engineers generally will recommend a traffic signal when accidents involving vehicles approaching from different directions occur at an abnormally high frequency, but only if a signal will have a positive effect on safety and other remedies to prevent these accidents prove unsatisfactory. Rear-end collisions are not normally remedied by the installation of a signal.
 
Can signals actually contribute to accidents and congestion?
Definitely. Even though they are valuable tools, traffic signals are not a cure-all for every problem intersection. A signal in the wrong location can contribute to rear-end collisions, excessive delays, unnecessary travel on alternate routes and a more congested traffic flow.

How do traffic signals work?
Traffic signals in Virginia work in two different ways: fixed time and traffic responsive. Fixed time traffic signals assign the green light to the different approaches of an intersection for a predetermined amount of time. Some of them also can be set to change to different green times during peak traffic hours. These type of signals can be found in urban areas where traffic movements are fairly predictable.
Traffic responsive signals change the lights according to the amount of traffic in each direction. These signals use sensors to detect the number of vehicles and automatically adjust the length of the green time to allow as many vehicles as possible through the intersection before responding to the presence of vehicles on another approach.

How often are traffic signals retimed to account for changing traffic patterns?
Our signals are connected to centralized computer systems. These systems continuously monitor the operational status of the signals, collect traffic flow information and support signal-timing operations and changes such as time of day and congestion levels.
Our Smart Signal System allows our engineers to continually adjust the signals in response to changing traffic patterns or accidents.

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