Question 1: What is the purpose of a traffic signal?
Answer: Traffic signals are electronically operated traffic control devices which alternately direct traffic to stop and to proceed. Traffic signals are designed to ensure an orderly flow of traffic, provide an opportunity for pedestrians or vehicles to cross an intersection and help to reduce the number of conflicts between vehicles entering intersections from different directions.
Question 2: How do traffic signals work?
Answer: Traffic signals are intended to facilitate the orderly movement of traffic. As the most restrictive form of traffic control, traffic signals are installed only where less restrictive signs or markings do not provide a sufficient level of control. Most intersections would not necessarily be improved or made safer by the installation of a traffic signal. Unnecessary signals cause wasteful and annoying delays to the flow of traffic. They can increase traffic on the side streets as drivers seek alternative routes through neighborhoods. Excessive starting and stopping burns needless amounts of gasoline, resulting in pollution and economic loss. And as previously mentioned, they can increase the total amount of crashes at an intersection.
Question 3: How many signalized intersections are there in Pennsylvania?
Answer: There are approximately 14,000 signalized intersections in Pennsylvania as indicated under the Mapping and Spread Sheets tab.
Question 4: As indicated with Pennsylvania Code Title 67, Chapter 212; how does PennDOT decide whether a traffic signal should be installed on a State Highway?
Answer: The Department follows federal guidelines (Manual on Uniform Traffic Control Devices - MUTCD) that establish minimum conditions under which a signal installation should be considered. From these federal guidelines, the Department has developed guidelines in Pennsylvania Code Title 67, Chapter 212). Both the MUTCD and PA code (Title 67) Chapter 212 provide a process for the traffic engineer to follow while investigating conditions and circumstances regarding the installation of a new traffic signal or improve the operation of an existing traffic signal. They contain criteria (warrants) which are used to define the need for, and appropriateness of a particular traffic control device. These warrants are usually expressed in the form of numerical requirements such as the volume of vehicular or pedestrian traffic. Warrants should be viewed as guidelines, not as absolute values. However, if no warrants are met, a signal will not be installed. Satisfaction of a warrant is not a guarantee that the signal is needed. The warrant analysis process is just one of the tools to be used in determining if a traffic signal is necessary. Engineering judgment should be exercised in making the final determination.
Question 5: I know of a traffic signal that has indications out or appears to be malfunctioning. Who do I contact?
Answers: Contact your local municipality and report the location (if possible provide the traffic signal identification number) and description of the malfunction.
Question 6: How do I go about getting a traffic signal installed at an intersection?
Answer: The Department should acknowledge receipt of any request by the general public and should advise the individual or party to refer their request to the proper local municipality since the local authorities would be responsible for all costs associated with any installation cost as well as future operation and maintenance costs. The local municipality can then make a request to the District, which will write an appropriate letter of acknowledgement. This letter may suggest a meeting, where if it appears that an official application (Form TE-952, Application for Permit to Install and Operate traffic Signals) should be executed, the District will provide a blank application form and a request for a condition diagram (and guidelines for its preparation). The Department will then determine based on the returned completed application if the location meets warrants for a signal, and if the municipality agrees to operate and maintain the signal on an ongoing basis after it is installed. If all these conditions are satisfied a traffic signal permit may be issued.
Question 7: What is a Traffic Signal Maintenance Agreement?
Answer: A Traffic Signal Maintenance Agreement is a legal written agreement between government agencies that describes the ownership, maintenance, and operational responsibilities of the municipality on Federal and/or State funded projects.
Question 8: What is the meaning of pedestrian symbols?
Answer: The white walking person or "walk" indication is to get the pedestrian off the curb and into the crosswalk. The orange flashing hand or "flashing don't walk" indication means don't start walking if you haven't left the curb but continue walking if already in the crosswalk. The steady hand or "don't walk" means you should no longer be in the crosswalk.
Question 9: How is the pedestrian “walk” and “flashing don’t walk” time determined?
Answer: The "walk" time is normally 4 to 7 seconds. Generally, the "don't walk time" is determined by the length of the crosswalk divided by the walk rate (normal walk rate is 3.5 feet per second).
Question 10: How does a traffic signal know when a vehicle is present?
Answer: The controller (computer) of the traffic signal will receive messages from the vehicle detection system of the traffic signal. The most common vehicle detection system that is utilized is the inductive loop detector in the roadway. A loop of wires, in the pavement, along with electronics in the traffic signal cabinet will detect the metal of a vehicle and send a "call" to the controller. Other types of detection systems are video, sonic and microwave.
Question 11: How is the yellow time of a traffic signal determined?
Answer: The largest factor in determining the appropriate yellow time is the posted speed limit of the roadway. Yellow time is used to notify traffic approaching the intersection that the signal is going to change to red to clear. Therefore, yellow times increase as the speed limit increases because stopping sight distance increase. The yellow time should be set so that approaching traffic is provided adequate amount of time to effectively stop based on the stopping sight distance. For more information reference Publication 149, Chapter 11 (Traffic Signal Timing).
Question 12: How is the all red time of a signal determined?
Answer: The purpose of the all red time is to allow vehicles that entered the intersection prior to the red to clear, adequate time to clear the intersection before conflicting traffic receives a green. The largest determining factors in all red timing are the width of the intersection and the posted speed limit of the roadway. Therefore, the all red time will increase as the width of an intersection increases and the speed limit decreases. For more information reference Publication 149, Chapter 11 (Traffic Signal Timing).
Question 13: I’ve seen a white light at a traffic signal, what does it mean?
Answer: The white light at some traffic signal is an Emergency Vehicle Preemption (EVP) indication. When this indication is on, it means an emergency vehicle is in the area and has preempted the traffic signal. Preemption will give the emergency vehicle the green light for safe and efficient passage thru the traffic signal. In addition, in locations where railroads are present, the white light can also mean the railroad has preempted the traffic signal and a special railroad preemption program is in operation. If the light is on steady it means that the signal has been preempted and will provide a green for that direction. If the light is flashing it means that the signal has been preempted to give a green for a different direction.
Question 14: Why do I have to wait when there’s no one coming?
Answer: Older signals don't have the necessary equipment to detect when cars are approaching, so green times are set longer. Minor streets get less green time than major streets so that the higher volumes can keep moving and don't build up. Pedestrian crossing times (Walk and Don't Walk) may require longer green intervals. A group of cars may come from one direction, then there might be a gap before cars arrive from the other direction.
Question 15: Are traffic signal indications using light emitting diodes (LEDs) in conformance with the MUTCD?
Answer: Yes, as long as they comply with the applicable ITE standards. The MUTCD does not specify the type of light source used for traffic control signal indications. Section 4D.18 states, "Support: Research has resulted in signal optical units that are not lenses, such as, but not limited to, light-emitting diode (LED) traffic signal modules." It also states, "Standard: References to signal lenses in this section shall not be used to limit signal optical units to incandescent lamps within optical assemblies that include lenses." However, Section 4D.18 also requires the design, illumination, and color all signal indications, including those using LEDs, to meet the requirements of the "Standards for Vehicle Traffic Control Signal Heads" published by the Institute of Transportation Engineers (ITE). The intensity and distribution of light from each illuminated signal lens should also conform to the ITE standards. ITE updated those standards in 2005 (information available at http://www.ite.org/standards/led.asp).
Question 16: Are strobe lights allowed in red signals?
Answer: No, they are not allowed. There are no provisions in Part 4 of the MUTCD that allow the use of strobes within red traffic signals. Section 4D.18 requires the design, illumination, and color all signal indications, including those using LEDs, to meet the requirements of the "Standards for Vehicle Traffic Control Signal Heads" published by the Institute of Transportation Engineers (ITE), and those standards do not provide for strobes as part of the design. Research and experimentation over the years with white strobe lights as a circular "halo" outer ring around the red signal or as horizontal bar across the red signal has found no lasting safety benefit and, in some cases, the strobes resulted in increased crash frequency. Based on this experience, FHWA made a determination in 1990 no further experimentation with strobe lights in traffic signals would be approved and that all existing strobes were to be removed. In 1995 a report by the Virginia Transportation Research Council provided an updated review of strobe light effectiveness in the States where they had been used. That report validated the previous analyses and came to the same basic conclusion, that there is no evidence that strobe lights are consistently effective in reducing crashes. Therefore, it is still FHWA's position that strobe lights are not allowed in traffic signals and no further experimentations with these types of strobe lights in traffic signals will be approved. This position was formalized in July 2003 with an Official Interpretation of the MUTCD, number 4-263(I).
Frequently asked questions regarding traffic signals.