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Transportation & Engineering - Traffic Signals

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1. What do I do when I see a dark or flashing traffic signal?

To report a traffic signal intersection that is entirely DARK or FLASHING outside of business hours (Monday through Thursday, 8:00 a.m. to 5:00 p.m.), please call the Jefferson County Sheriff’s Office at 303-980-7300. During business hours, contact the Jefferson County Transportation and Engineering Division at 303-271-8495.

If a traffic signal is entirely dark or flashing, Colorado State Law dictates that motorists shall treat the intersection as all-way stop control, unless an officer is directing traffic.

2. What happens to Jefferson County traffic signals when they lose power?

Typically, the traffic signal will go dark. Some traffic signals have a battery back-up system that can maintain either normal or flashing operation of the traffic signal for a few hours.

3. Who regulates traffic in Jefferson County?

The Jefferson County Transportation and Engineering Division maintains traffic control devices, regulates traffic, and studies traffic flow to ensure safety and efficiency.  The Manual on Uniform Traffic Control Devices (MUTCD) is followed to determine the appropriate use of traffic devices.  These guidelines require certain criteria be met before a device can be used, and ensure that motorists experience consistency between communities throughout the United States.

4. Who builds and maintains traffic signals in Jefferson County?

Contractors build traffic signals in Jefferson County as part of capital improvement and safety projects, or larger private developments.  All traffic signals on the Jefferson County roadway system are owned and operated by the county once constructed.  Please refer to the Signalized Intersection List (PDF), for all traffic signals owned and maintained by the county.

Traffic signals located along state highways, (e.g. SH-93, SH-58 and at on-and-off ramps to C-470), are maintained by the Colorado Department of Transportation (CDOT).

Traffic signals located within incorporated cities or towns (e.g. Arvada, Lakewood, Golden, etc.) are maintained and timed by the respective local jurisdiction.

The Transportation and Engineering Division maintains traffic signals on unincorporated county roads. Much of the maintenance work performed on traffic signals is done by the county’s contractor.

5. How do traffic signals work?

Traffic signals are made up of many components and pieces of equipment to ensure that the signal operates safely and efficiently. Two of the most important components are the controller and detectors.

The controller is a computer that is programmed with various parameters that dictate how the signal operates, such as minimum and maximum green times, pedestrian walk times, and cycle lengths.

The detectors determine when a vehicle, pedestrian, or bicycle is present and pass this information to the controller. There are various types of detection systems, including video, thermal, electromagnetic loops in the pavement, and radar. Once the controller knows that traffic is waiting to receive a green light, it will incorporate that information into its programming as it runs through phases and cycles.

If a traffic signal appears to be operating unusually, such as not providing a green light to traffic or providing a green light to streets that have no traffic waiting, please contact Transportation and Engineering.

6. Who maintains flashing school zone beacons?

The school zone beacons on roads within unincorporated Jefferson County are maintained by the Transportation and Engineering Division.  They are programmed to turn on during each school’s arrival and dismissal periods (including midday kindergarten).  Traffic staff confirms arrival and dismissal times through Jefferson County Public Schools on an annual basis.

Please report malfunctions to Transportation and Engineering.

7. How does the county decide when a traffic signal should be installed? Will a traffic signal reduce accidents at an intersection?

Traffic engineers follow the national standards described in the Manual on Uniform Traffic Control Devices (MUTCD). The MUTCD mandates that a traffic signal cannot be installed unless the intersection has met the requirements of one or more traffic signal “warrants.” These warrants consider various criteria when evaluating the intersection, such as vehicle volumes, pedestrian volumes, and crash history.

Traffic signals can improve traffic flow and increase safety when used properly. However, traffic signals are not always the right solution and do not always prevent accidents. For example, a traffic signal may reduce the number of right-angle collisions at an intersection, but the number of rear-end crashes may increase.

To request that an intersection be evaluated for traffic signal control, please contact Transportation and Engineering.

8. What is the purpose of cameras at signalized intersections?

Jefferson County uses two types of cameras at signalized intersections: detection cameras and traffic monitoring cameras.

Detection Cameras - These cameras use video technology to detect when a vehicle approaches a signalized intersection and are typically mounted on each leg of an intersection. They can be susceptible to false calls when heavy shadows, glare, or snow occur. Please report malfunctioning traffic signals to Transportation and Engineering.

Traffic Monitoring Cameras - These cameras are used by traffic staff to monitor traffic patterns or to check on traffic signal operations. These cameras can be watched live by staff during peak travel periods or when an accident occurs. The county does not store footage from the cameras.

9. Are traffic signals in Jefferson County coordinated to reduce or eliminate the need to stop at red lights?

Most Jefferson County traffic signals are programmed based on the time of day, the location, traffic patterns, and traffic volumes. There are many factors that can affect the design of timing plans, such as the volume of traffic on the side streets, the crossing time required for pedestrians, the distance between traffic signals, the speed limit on the main street, the total overall traffic volume, the number of turning vehicles, and the number of lanes available for each movement of traffic.

Most of Jefferson County’s traffic signals operate on three different timing plans, which include weekday AM Peak, PM Peak, and Off-Peak plans. There are also special plans for weekends. There are also some timing plans implemented for unique circumstances, like school traffic, heavy lunchtime traffic, or holiday shopping traffic.

There are numerous factors that can impact the effectiveness of traffic flow that unfortunately cannot be accounted for in the traffic signal’s programming, such as the actual speed of traffic, the acceleration patterns of motorists, variations in the volume of traffic during the timing plan, the frequency of emergency vehicle pre-emption, and the frequency of pedestrians (having pushed the button to cross) each cycle.

10. Once a driver turns onto a street where the traffic signals are coordinated, is it correct that the driver should not have to stop?

Progression of traffic on streets with coordinated traffic signals is typically designed to move traffic that came straight through the previous signalized intersection. If a driver turned onto the major street from a side street, the driver may need to stop one or more times before getting into the flow of traffic.

11. Do any traffic signals not run in coordination with other traffic signals?

Very few of the traffic signals in Jefferson County are constantly run in “free” mode, meaning they are not coordinated with other signals. When a signal runs in free mode, it does not have to maintain timings that keep it in coordination with adjacent signals, therefore it can quickly change in order to give the green light to a vehicle that has approached and stopped at a red light. Free operation is efficient at locations that have very low volumes, are not near any other traffic signals, or have other unique conditions. Although most of the traffic signals in the county run coordinated during the day, they switch to free operations during the overnight hours when traffic volumes are very low.

12. Why is there a “Walk” symbol when no pedestrians are present?

The green time for the major street traffic is typically long enough that there is enough time for a pedestrian to safely cross the minor street, so the Walk symbol is displayed to facilitate pedestrian mobility.

Sometimes, especially in freezing temperatures, a pedestrian push button will get “stuck.” This will cause the signal to bring up the Walk display even when no pedestrians are present and can negatively impact traffic flow if it occurs for a major street crossing. Please report issues to Transportation and Engineering.

13. How do signals for pedestrians work?

When a pedestrian pushes the button on the signal pole, a call is sent to the computer that controls the traffic signal (the controller). The controller will see this request for a “Walk” indication. The call is constant, meaning that as long as the button has been pushed once, the controller knows to give the Walk phase. At the appropriate time, based on the parameters of the signal’s timing plan, the “Walk” symbol will be displayed. Pushing the button multiple times will not cause the traffic signal to bring up the Walk phase any sooner.

The “Walk” symbol (a steady walking person) means that a pedestrian facing the signal indication is permitted to start crossing the road.

The flashing “Don’t Walk” symbol (a flashing upraised hand) means that a pedestrian shall not start to cross the road, but that any pedestrian who had already started to cross on the “Walk” symbol can finish crossing the roadway and will have enough time to safely do so. The countdown display next to the flashing hand shows the number of seconds remaining until the end of the crossing time.

The steady “Don’t Walk” symbol (a steady upraised hand) means that a pedestrian shall not enter the roadway.

14. Why do I have to wait so long to get a green light or a “Walk” signal?

Traffic signals that run with coordinated operations are part of a corridor of connected traffic signals that run a timing plan which ensures traffic along the route can flow properly. When the traffic signals are timed efficiently, vehicles traveling along the corridor experience a “green band,” which means that they will receive consecutive green lights along the corridor and not be stopped at every side street. In order for the signals to be coordinated, there are specific points in the timing cycle where the side street can turn green.

Drivers waiting at a side street may experience seemingly long waits because the side street’s operations are constrained by the timing plan of the corridor. Reducing the length of the red light time for drivers (or “Don’t Walk” for pedestrians) waiting on the side street would impact the coordinated nature of the major street corridor, leading to an overall increase in delay.

Traffic signals are programmed with various other timing parameters that serve to minimize overall delay at an intersection. However, if the wait time is more than 120 seconds, there may be a problem with the traffic signal. If this occurs, please contact Transportation and Engineering.

See Signal Intersection List (PDF) to determine if the county is responsible for the traffic signal.

15. Do emergency vehicles get priority at signalized intersections in Jefferson County?

Emergency vehicles associated with the fire districts are equipped with a special device that gives them the ability to change the traffic signals to green for the direction that the emergency vehicle is traveling. Law enforcement vehicles and private ambulance companies usually do not have this ability.

16. Is it possible for two conflicting directions of traffic at a signalized intersection to receive green lights at the same time?

Traffic signals are equipped with conflict monitors that are designed specifically to detect equipment errors and prevent this from happening. If the conflict monitor detects a potential conflict, it puts the entire intersection into flashing operation. The intersection will remain in flash operation until a technician can fix the problem.

Occasionally, accidents or strong winds rotate signal heads so that the lights are visible to the wrong direction of traffic. Please report damaged or rotated traffic signal equipment to Transportation and Engineering.

17. How does a flashing yellow left-turn arrow work?

A flashing yellow arrow means that left turns are permitted, but drivers must first yield to oncoming traffic and pedestrians and then proceed with caution. The flashing yellow means the same thing as the green "ball" indication for a yielding left turn. The flashing yellow arrow does not replace the solid yellow arrow and its meaning.

• Solid green arrow = Left turns have the right-of-way
  • Drivers may proceed and must turn left.  Oncoming traffic and pedestrians are stopped.
• Flashing yellow arrow = Turns are permitted when there are acceptable gaps in traffic
  • Drivers must yield to oncoming traffic and pedestrians, then proceed with caution.
• Solid yellow arrow = Signal is about to change to red
  • Drivers may only complete their turn if they legally entered the intersection and there are no conflicting vehicles or pedestrians.
• Solid red arrow = Stop
  • Drivers turning left must stop.