The following information is provided by the Traffic Improvement Association (TIA).
Crashes & Collisions
Traffic signals don't always reduce crashes. In many instances, the total number of crashes remains unchanged after signals are installed. However, the severity of right-angle crashes is exchanged for less injury-producing rear-end crashes.
Where signals are used unnecessarily, the most common results are a reduction in right-angle collisions but an increase in total accidents, especially rear-end type collision. In addition, pedestrians are often lulled into a false sense of security at signalized intersections.
Asset or Liability
In deciding if a traffic signal will be an asset or a liability, traffic engineers consider the following:
- Do the vehicles on intersecting streets create confusion or congestion?
- Is traffic on the main street so heavy that drivers on the side street will accelerate when it's unsafe?
- Do the pedestrians trying to cross a busy main street create confusion, congestion or hazardous conditions?
- Do the school children crossing a street require special traffic controls for their protection? If so, is a traffic signal the best solution?
- Will the installation of a signal allow for continuous, uniform traffic flow with a minimum number of vehicle stops?
- Does the crash history indicate that a signal will reduce the possibility of a collision or reduce the level of injuries?
Existing Conditions & Nationally Accepted Minimum Standards
Traffic engineers compare the existing conditions against nationally accepted minimum standards established after many years of studies throughout the country. At intersections where standards have been met, the signals generally operate effectively with good public compliance. Where Warrants are not met, compliance is generally reduced resulting in additional risks.
Sources of Danger
While a properly placed traffic signal improves the flow and decreases injuries, an unnecessary signal can be a source of danger and annoyance to all that use an intersection-pedestrians, bicyclists and drivers.