Traffic Signals FAQs
Traffic signals are one of the most asked-about features on roadway systems. They give drivers gaps to enter the roadway, provide pedestrians with a convenient place to cross the street and control the flow of traffic through an intersection. Here are some of the most frequently asked questions and answers about traffic signals.
If there aren't any road improvements needed, such as adding turn lanes, then a complete traffic signal system for a typical four-way intersection will cost about $250,000 to $300,000. When additional costs like control equipment, project inspection, and design are taken into account the cost edges closer to $300,000. There are also ongoing costs for electricity, painting, re-lamping, and other maintenance.
The white floodlights on signal arms are activated by emergency vehicles and are lit when the system overrides its normal timing program. Emergency vehicle preemption (EVP) is activated by a special transmitter within the emergency vehicle. EVP forces the system to give a green light to the correct approach, thereby reducing emergency response times and the risk of a crash. In most states, including Minnesota, it is illegal to possess one of these devices unless you’re driving an emergency vehicle. New EVP systems allow the system to only recognize strobe signals with an embedded code, making non-emergency or unscrupulous use impossible.
Traffic signals operate in a few different ways depending on location. In the City of Woodbury traffic signals usually operate in one of two ways: using vehicle detectors, usually a wire loop buried in the pavement, or via video detection, which uses cameras mounted on mast arms or signal poles. The vehicle detector loops work like a metal detector, sensing the car’s magnetism not weight. Video detection uses a camera that can recognize an approaching vehicle (Radio Drive/Lake Road and Tamarack Road/Interlachen Parkway use video detection). In both of the systems, the detectors send a signal to a computer, which then changes the light. The signals do have some fixed timings entered, such as minimum and maximum green times, yellow time, or pedestrian timing, but otherwise the signal responds to the traffic that is present. In the middle of the night, the signal might stay green for hours in the same direction if there’s no traffic.
A traffic signal should not be expected to reduce the total number of crashes at an intersection. Traffic signals in Minnesota, according to a 2001 study, have a statewide crash rate of between seven and eight crashes for every 10 million entering vehicles. An all-way stop has an average crash rate of six crashes for every 10 million entering vehicles, and a two-way stop has an average of only four crashes per 10 million entering vehicles. Of course this can depend on other site conditions as well, but on average, a signal will reduce right-angle crashes while causing an increase in rear-ends and an overall increase in crashes. Unfortunately, drivers occasionally run red lights or fail to notice stopped traffic in front of them. Many of the city’s serious and fatal crashes occur at traffic signals. Therefore it is very important to study an intersection to measure the need for a traffic signal.
Traffic signals are usually warranted based on minimum traffic volumes during eight hours of a typical weekday. These minimum volumes, or “warrants”, vary depending on the speed of the roadway and the number of approach lanes. For a signal to be approved, it needs to meet the necessary warrants and be justified. To be considered “justified”, factors such as access and distance to nearby signals, lane geometry, and future road plans are all taken into account. If all the necessary conditions are satisfied, and funding is available, a signal may be installed.
The “Walk” light isn’t supposed to stay on for more than a few seconds. The state standard is seven seconds, but can be as little as five seconds. The “Walk” light means that it’s okay to start crossing. If you started crossing at the transition from “Walk” to a flashing “Don’t Walk” sign, it should flash long enough for most people to make it all the way across the road before the “Don’t Walk” stops flashing and the light starts to change. When the signal is flashing “Don’t Walk”, it is safe to finish crossing the intersection; however, it is not safe to enter the crosswalk at this time. When the “Don’t Walk” stops flashing and the light changes, it is unsafe to cross the road.
Minnesota policies generally require that left turns be “protected” (green arrow only) when the speed limit of the oncoming traffic is over 40 miles per hour, when there are dual left turn lanes, when turning volumes are high, or when sight lines are restricted. Relaxing the policy would reduce wait time at traffic signals and save fuel, but would also likely cause an increase in crashes. With the rising cost of fuel, it is possible that this standard could be re-evaluated. The use of alternative signal indications to allow left turns, such as a flashing yellow arrow, is being tested across the country. So far, the results are promising. If approved for use, these indications could replace some of the traditional phasing, thereby reducing delay.
All traffic signals in the City of Woodbury rely on detectors to maximize efficiency. Traffic signals typically will not turn red for the main highway until the detectors sense a gap in the traffic or the maximum time for a green light is reached. This is designed to increase efficiency and safety by reducing the number of vehicles confronted with a yellow light. Unfortunately, gaps in traffic often occur when a large platoon of traffic is approaching but is out of range of the detectors. This causes the entire platoon of vehicles to arrive at a red light, sometimes for the benefit of just a few vehicles entering from the side street.Traffic signal systems can be coordinated, but doing so will typically lead to longer wait times for side street traffic and for left turns. When traffic signals are coordinated they operate on a fixed timing cycle to remain in step with each other. The cycle must be long enough to accommodate the busiest intersection in the corridor. While this coordination can be a benefit, it is costly to implement and will typically increase the wait time to enter a highway. Three coordinated corridors are currently operating in the City of Woodbury. All three are on the Washington County highway system. The coordinated corridors are:
- Radio Drive from Pinehurst Road to 4th St North.
- Radio Drive at Valley Creek Road and adjacent intersections to the north, south
- Valley Creek Road from Tower Drive to Weir Drive (coordination plans being implemented in the fall of 2008).
In the future, Washington County staff will focus efforts on adding corridors and updating the timing plans for existing systems in order to adapt to changing traffic patterns.
When a traffic signal malfunctions but still has power, it will often revert to an all-red flashing mode. When you approach a signal light that is flashing red, you must come to a complete stop (Mn Statute 169.06, Subd. 7). Sometimes the traffic signal will flash red in all directions, making the intersection operate like a four-way stop. At some intersections, the lights may flash yellow for the main roadway, thus making the intersection function like a two-way stop. Always stop at a traffic signal that is flashing red, and be sure it is safe before entering the intersection as the cross traffic may not be required to stop. If you approach a flashing yellow light, you do not need to come to a complete stop. However, be alert for drivers entering the intersection and proceed with caution.Signals that are in flashing mode can return to normal operation at any time and without warning, even when repair workers are not present. The flashing red may change to a solid red, and drivers often fail to notice the difference, running the red light. Proceeding on a solid red light is always illegal and can lead to a deadly crash. Be alert, and make sure that the light is still flashing and that it is safe to proceed before entering the intersection.
During the severe weather season, it is not unusual to have power outages due to high wind or lightning strikes. Traffic signals throughout the city rely on electricity to function. If a traffic signal is in an area of a power outage, it will go dark.If you approach a traffic signal without power, remember that the rules of right-of-way still apply. You should:
- Slow down and prepare to stop.
- Determine who has right-of-way to proceed through the intersection.
If there is a lot of traffic at the intersection, it will naturally begin to function as a four-way stop. Remember that vehicles have right-of-way in the order in which they arrive regardless of which road they arrive from. If two vehicles arrive at the intersection at approximately the same time, the vehicle on the left must yield to the vehicle on the right, and left turns must yield to oncoming traffic.Always assume that other drivers may react unpredictably or that they may not even slow down when driving through an uncontrolled intersection. Drive defensively, even if it means waiting beyond “your turn” to proceed through the intersection safely.To report a signal malfunction, call the Washington County Sheriff’s Office dispatcher at (651)439-9381. If it is an emergency, call 911.
A flashing yellow arrow signal has the same meaning it always has: left turns may proceed with caution after yielding to oncoming traffic. When approaching a flashing yellow arrow, drivers are allowed to turn left after yielding to all oncoming traffic and to any pedestrians in the crosswalk. Oncoming traffic has a green light. Drivers must wait for a safe gap in oncoming traffic before turning. To learn more about flashing yellow arrows, visit the Minnesota Department of Transportation website.
Within the City of Woodbury, traffic signals are generally owned by the City, Washington County, or the Minnesota Department of Transportation (MnDOT). The following rules are generally true, but there are exceptions:
- Signals at interchange ramps and loops are owned by the state.
- Signals at all intersections involving at least one state road are owned by MnDOT.
- Signals at intersections involving a county road are owned by the county.
- Signals at intersections that only include city roads are owned by the city.
To report a signal malfunction, contact the highway department responsible for the signals. For signals on state highways in the City of Woodbury, contact MnDOT at (651) 234-7500. For signals on Washington County roads, such as Radio Drive (CSAH 13), Woodbury Drive (CSAH 19), and Valley Creek Road (CSAH 16), call Washington County Public Works at (651) 430-4300. For city signals, contact the City of Woodbury Public Works Department at (651) 714-3720. In an emergency, dial 911.