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Workers installing a traffic signal.

 

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We will direct your question to the appropriate person and/or agency.

 

Traffic signal design or operation on Mn/DOT projects

 

Contact Jerry Kotzenmacher

 

email Jerry.Kotzenmacher@state.mn.us

call 651-234-7003

 

 

 



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Answers


Question: I know of a traffic signal that has indications out or appears to be malfunctioning. Who do I contact?

 

Answer: First, you need to know which government agency owns and operates the traffic signal (city, county or MN/DOT). Generally, if a state highway has an approach to the traffic signal, then MN/DOT is likely to operate the signal. If no state highway is present, only county or city roads approach the signal, then the county in which the signal is located is likely to operate the signal. If no state highway or county road is present at the signal, only city streets approach the signal, then it is likely that the city in which the signal is located will operate the signal. Once the operation and ownership of the signal is determined, you can contact the agencies Traffic Engineering/Public Works department. Click here

 

 

Question: How do I go about getting a traffic signal installed at a intersection?

 

Answer: First, you need to know which government agency has jurisdiction of the roadways approaching the intersection (city, county or MN/DOT). Generally, if a state highway approaches the intersection, then MN/DOT has jurisdiction of the intersection. If no state highway is present, approaches are only county or city roads, then the county in which the intersection is located has jurisdiction. If no state highway or county roads are present, all approaches are city streets, then the city in which the intersection is located has jurisdiction. Once the jurisdiction of the intersection is determined, you can contact the agencies traffic engineering/public works department. Click here

 

Question: What criteria are required for a traffic signal to be installed?

 

Answer: The intersection must meet one or more "signal warrants" explained in the Minnesota Manual On Uniform Traffic Control Devices.
Click here

 

 

 

Question: What is a signal agreement?

 

Answer: A signal agreement is a legal written agreement between government agencies that describes the ownership and maintenance responsibilities of the agencies for the traffic signal.

 

Question: I was involved in an accident at a traffic signal. How can I get the timing and the sequence of the traffic signal?

 

Answer: First, you need to know which government agency owns and operates the traffic signal (city, county or MN/DOT). Generally, if a state highway has an approach to the traffic signal, then MN/DOT is likely to operate the signal. If no state highway is present, only county or city roads approach the signal, then the county in which the signal is located is likely to operate the signal. If no state highway or county roads are present, all approaches are city streets, then it is likely that the city in which the signal is located will operate the signal. Once the operation and ownership of the signal is determined, you can contact the agencies Traffic Engineering/Public Works department. Click here


Since many traffic signals respond to the presence of vehicles approaching the intersection, the actual length of the green light can be different every time the green comes up. Therefore, it may not be possible to know the exact timing and sequence of the signal at the time of the accident.


Question: 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.


Example: If at any time a pedestrian is in a crosswalk and the "flashing don't walk" just starts, the pedestrian will have enough time to walk (at a normal walk rate) the entire length of the crosswalk, to the curb or refuge. The "walk" symbol is only meant to get the pedestrian off the curb and start walking.



Question: How is the pedestrian "walk" and "flashing don't walk" time determined?

 

Answer: See meaning of pedestrian symbols. 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 4 feet per second).

 

 

Question: 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 MN/DOT utilizes 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. The vast majority of MN/DOT traffic signals have some type of vehicle detection.



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Question: How is the yellow time of a traffic signal determined?

 

Answer: MN/DOT uses yellow time of 3.0 seconds to 6.0 seconds. The largest determining factor in yellow time is the posted speed of the roadway. Generally, the slower the posted speed limit, the shorter the yellow time and the faster the posted speed limit, the longer the yellow time. The yellow time must be long enough so that a vehicle traveling at the speed limit that is too close to the intersection to stop when the yellow comes up will be able to enter the intersection on yellow before the light turns red.


Example: if the roadway is posted 55mph, the yellow time should be around 5.5 seconds.

 

 

Question: How is the all red time of a signal determined?

 

Answer: The all red time is the time from when the light turns red for one approach until the light turns green for a conflicting approach. The purpose of the all red time is to allow vehicles that entered the intersection before the red to clear the intersection before conflicting traffic receives a green. MN/DOT uses all red time (all approaches to traffic signal are red) of 1.0 second to 4.0 seconds. The largest determining factors in all red timing are the width of the intersection and the posted speed limit of the roadway. Generally, the larger the width of the intersection and the slower the speed limit, the longer the all red time. In contrary, the shorter the width of the intersection and the faster the speed limit, the shorter the all red time.

 

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Question: 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: What is the difference between a traffic signal and a ramp meter?

 

Answer: A ramp meter is a traffic control device located at "on ramps" for freeway access. A traffic signal is a traffic control device for two or more intersecting roadways.

 

 

Question: What manuals, standards, sample plans, specifications are available for review and guidance for traffic signals?

 

Answer: Check the Design Tools of the Mn/DOT's OTSO website and/or the Publications Section of the website for a listing of available online documents.

 

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