Douglas County Traffic Signals - Frequently Asked Questions
Updated October, 2009
Douglas County Traffic receives numerous inquiries about our traffic signal system. The following are answers to frequently asked questions (FAQ's).
When reporting a malfuntioning traffic signal or for questions about the "timing" of traffic signals in any part of Douglas County, please view the Signalized Intersection List first to determine the appropriate agency to contact.
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Do any traffic signals not run in coordination with other traffic signals?
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Why do green left turn arrows appear at different times during different times of the day?
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Why do I have to wait so long to get a green light or a WALK signal?
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What are the blue lights that are installed at some traffic signals?
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What are the Douglas County Traffic Management Centers used for?
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What happens to Douglas County traffic signals when they lose power?
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Can I learn more about what Douglas County Traffic does? Can I see how traffic signals work in person?
Q. Who builds traffic signals in Douglas County?
Traffic signal contractors build traffic signals in Douglas County on behalf of private developers, metropolitan districts, or Douglas County. All traffic signals on the Douglas County roadway system are owned and operated by Douglas County once constructed. To determine who owns and operates various intersections, please view the Signalized Intersection List [Approx. 43KB PDF]
Q. Who maintains traffic signals in Douglas County?
It depends. Refer to the Signalized Intersection List [Approx. 43KB PDF], or see below.
Traffic signals located along state highways (US-85 (Santa Fe Drive), SH-83 (Parker Road) and at most on- and off-ramps to I-25 and SH-470 (C-470), are maintained by the Colorado Department of Transportation (CDOT). The current exceptions are the on- and off-ramps at Quebec/C-470 and Lucent/C-470, which are maintained by Douglas County, and Yosemite/C-470 and Lincoln/I-25, which are maintained by Lone Tree.
Traffic signals located within incorporated cities or towns (Castle Rock, Lone Tree, Castle Pines and Parker) are maintained and timed by the respective local jurisdiction.
On unincorporated county roads (including roads within Highlands Ranch and Roxborough communities), Douglas County Traffic maintains the traffic signals. Douglas County Traffic signal maintenance staff is augmented at times with on-call contractors.
Q. Who maintains Flashing School Zone Lights?
The School Zone Flashers on roads withing unincorporated Douglas County are maintained by Douglas County Traffic personnel. They are set to turn on for the school's start times and stop times (including kindergarten - typically around noon). Douglas County Traffic confirms start/stop times for each individual school annually by contacting the schools. The units are pager-activated and, unfortunately, malfunctions do occur. Please report apparent malfunctions to Engineering – Traffic at 303.660.7490 or at traffic@douglas.co.us.
Q. Will a traffic signal reduce accidents at our intersection?
Traffic signals can benefit the community and increase safety when used properly. However, traffic signals don’t always prevent accidents or help control traffic. In fact, while traffic signals can generally reduce the number of right angle collisions, the number of rear-end and pedestrian accidents may actually increase.
For example, many pedestrians feel secure with a painted crosswalk and a red light between them and an approaching vehicle. The motorist, however, may not be as quick to recognize these barriers, thereby creating a false sense of security for the pedestrian.
To decide whether a traffic signal should be installed, traffic engineers consider the following:
- Does the amount of traffic on intersecting streets create confusion or congestion?
- Is traffic on the main street so heavy that drivers on the side street will try to cross when it is unsafe?
- Do pedestrians trying to cross the busy street create confusion, congestion or hazardous conditions?
- Does the number of school children crossing a street require special controls for their protection? If so, is a traffic signal the best solution?
- Will a traffic signal at this location help drivers maintain a uniform pace along the route without unnecessary stops?
- Does the intersection’s accident history indicate that a traffic signal will reduce the possibility of a collision?
- Do two arterial roads intersect at this location, and will a signal improve the flow of traffic?
- Is there a combination of the above conditions that indicates a signal will be an improvement rather than a detriment?
Traffic engineers are required by state law to compare each situation with national standards established by studying intersections throughout the country. The Manual of Uniformed Traffic Control Devices (MUTCD) contains criteria known as “warrants”. Generally, warranted traffic signals control traffic flow effectively, while those that are not warranted may become additional hazards, and other solutions to a traffic problem should be investigated.
Q. What are the cameras at traffic signals for?
Douglas County uses several different types of cameras at signalized intersections:
Intersection Detection Cameras– These cameras use video detection technology to detect when a vehicle is approaching a signalized intersection. These cameras are typically mounted on each approach to a signalized intersection. They are susceptible to false calls when heavy shadows, glare and snow occur. Please report malfunctioning traffic signals to Engineering-Traffic at 303.660.7490 or traffic@douglas.co.us.
Video Surveillance Cameras – Closed Circuit Television (CCTV) cameras are used by traffic staff to monitor traffic patterns and check on traffic signal trouble calls received, prior to traveling to the location. These cameras are currently actively watched by staff only during peak travel periods or when trouble calls or accidents occur. The cameras can be viewed on monitors at the Traffic Management Centers.
Answers to Common Questions about these cameras:
- These cameras are not recorded on a full-time basis
- These cameras are not used for photo-enforcement of red-light running
- License plates are typically not legible in these cameras
Q. Do the Douglas County traffic signals “talk” to each other? Can maintenance staff “talk” to them remotely?
The majority of Douglas County’s traffic signals have the ability to communicate with each other and with the Douglas County Traffic Management Centers. This communication can be used for something as simple as making sure that all of the clocks at each signal are accurate, or for something more complicated like uploading or downloading revised traffic signal timing data. This communication is currently done primarily by means of fiber optic cable, radio and/or dial-up phone line. Douglas County is continuing to put more and more of its existing communications infrastructure onto fiber optic media. When a developer or a metropolitan district installs a traffic signal, Douglas County typically requires that improvements to provide traffic signal communications be included in the project, if necessary.
Q. Are traffic signals in Douglas County coordinated to reduce or eliminate the need to stop at red lights?
The majority of Douglas County traffic signals are coordinated (timed), depending on the time of day, the location, and (when applicable) the primary direction of travel. In order to maintain consistent coordination of our traffic signals, time clocks at each intersection must remain synchronized, usually by means of communications with the Traffic Management Center. Coordinating traffic signals to facilitate traffic flow in both directions simultaneously (for example, when there is no clear primary direction of travel) is much more complicated than simply facilitating traffic flow in only one direction (e.g. a one-way street). There are many factors that can affect the design of timing plans, including the:
- volume of traffic on the side streets
- crossing time required for pedestrians
- distance between traffic signals
- speed limit on the main street
- total overall traffic volume
- volumes of turning vehicles
- number of lanes available for each movement of traffic
Additional factors - over which Traffic personnel have no control - affecting the actual effectiveness of the timing plans include:
- 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 preemptions
- the frequency of pedestrians using the pedestrian signal (having pushed the button to cross) each cycle
Most of our traffic signals run three different timing plans. They are:
- AM Peak plan, Mondays to Fridays;
- PM Peak plan, Mondays to Fridays;
- Off Peak plan, Mondays to Fridays and weekends.
There are also additional timing plans in some locations for special circumstances, like school traffic, weekend, heavy lunchtime traffic, or holiday shopping traffic. When traffic signals are not running in coordination, they operate in one of several different possible modes that depend on the equipment available at each particular intersection.
As you can imagine, traffic signal timing is very challenging. For more information about traffic signal timing and the many challenges involved, please view the informational document “Why Are the Signals Always Red?” by the Denver Regional Council of Governments (DRCOG).
Q. Once I turn onto a street where the traffic signals are coordinated, I shouldn't have to stop, right?
Not necessarily. Progression of traffic on streets with coordinated traffic signals is typically designed to move traffic that came straight through the previous signalized intersection. If you turned onto the street from a side street, you may need to stop one or more times before you can get into the flow of through traffic. At some locations, it is necessary accommodate turning vehicles due to the volume of traffic. Those are evaluated on a case-by-case basis. Generally, this only occurs at major intersections.
Q. Do any traffic signals not run in coordination with other traffic signals?
Yes, that type of operation is referred to as actuated, demand-responsive, or “snappy” operation. This type of operation reduces the amount of time a vehicle has to wait for a green light when there is no conflicting traffic present. The decision to run a signal in a demand-responsive operation usually involves a number of factors including, but not limited to the following:
- distance to adjacent traffic signals
- volume of traffic
- availability of video detection
- other “odd” conditions like the presence of unique traffic generators (eg. Schools, large church, etc) on the side street.
Q. Why do green left turn arrows appear at different times during different times of the day?
“Traditionally”, green arrows for left turn traffic appear before the through traffic gets a green light. To minimize delay at coordinated signalized intersections, it is sometimes necessary to bring up one or both of the left turn green lights after the conflicting through traffic has received a red light. This type of left turn operation is called “lagging” left turn operation and is done under certain conditions for a number of reasons. The underlying reason, nevertheless, remains that at certain times of the day traffic engineers can get more cars through a signalized corridor that runs in coordination if they have the flexibility of lagging the left turns.
Q. How do signals for pedestrians work?
When a pedestrian pushes the button on the signal, a message is sent from the button to the computer that controls the traffic signal (the “controller”). The controller will see this request for a Walk light, and at the appropriate time, a Walk light will be provided. The button is like a light switch—after you have pushed it once, it is “on” and stays on until the Walk light appears. The standard time the Walk light is displayed is 5 seconds. When the Walk light comes up, you should begin to cross. Once the initial “Walk” time has passed, the “Flashing Don’t Walk” will appear—the flashing orange hand. This means that if you have not started to cross the road yet, you should not step off the curb. HOWEVER, if you are already in the process of crossing the road, the average pedestrian WILL have enough time to cross the entire road safely. Douglas County Flashing Don’t Walk time is based on the width of each particular roadway and the average walking speed of a pedestrian. Once the Flashing Don’t Walk time has passed, a solid “Don’t Walk” light will appear—the solid orange hand. This means that no pedestrians should remain in the intersection, as conflicting traffic has, or is about to receive, a green light. Some intersections are also equipped with “countdown” pedestrian heads, which display for pedestrians the exact number of seconds remaining before the pedestrian needs to be clear of the intersection.
Q. Why do I have to wait so long to get a green light or a WALK signal?
There are a number of reasons why drivers and/or pedestrians will find themselves waiting. Generally, if you actually time it and find yourself waiting for more than 120 seconds, there may be a problem with the traffic signal. If this occurs, please check the Signalized Intersection List [Approx. 43KB PDF] and call the appropriate agency. If the appropriate jurisdiction is Douglas County, call 303.660.7490 to report the problem.
- When a traffic signal is running in coordination with other traffic signals, it operates in a timed cycle. The coordination plan will allow the side street green light to appear only at a certain time in the cycle when it is designed to minimize the disruption of traffic on the main street. If you arrive after that time in the cycle, you will have to wait through one more cycle until that time comes around again. Cycle lengths range from 50 seconds to as much as 120 seconds, depending on time of day and the location.
- When a traffic signal is not running in coordination with other traffic signals and is set up for demand-responsive operation, the controller of the intersection will give the side street a green (or a Walk) as soon as there is an appropriate gap in main street traffic. If there are no gaps of sufficient length in main street traffic, the traffic signal will continue to display a green light for a pre-determined maximum time for the main street as in the previous item.
- When a traffic signal is not running in coordination with other traffic signals and cannot be set up for demand-responsive operation due to equipment limitations, the controller of the intersection times a certain minimum amount of time for the main street to remain green, usually between 20 and 25 seconds. Once this time has been reached, the side street will be given a green. Vehicles (and pedestrians) can arrive at any point during the timing of this maximum time and can therefore face a wait of anywhere from zero seconds up to this maximum time.
- If the signal is running in demand-responsive or coordinated mode, you may still find yourself waiting at a red light for what appears to be no noticeable reason. When this occurs, look for pedestrians who may have activated the pedestrian signal or fire trucks that may be approaching from any other direction. Both of these events can make motorists wait for an adequate time for them to safely travel through the intersection.
Q. What are the blue lights that are installed at some traffic signals?
The blue lights are used by the Douglas County Sheriff’s Office to identify vehicles that run red lights. They are also known as “tattletales”. The blue tattletale light turns on as soon as the corresponding direction’s traffic signal light turns red. When mounted correctly, the tattletale allows a deputy waiting safely down the road to watch for motorists running red lights.
Q. Do Fire Trucks, Ambulances and Law Enforcement Vehicles get priority at signalized intersections in Douglas County?
Fire trucks and ambulances associated with the fire districts are equipped with a special strobe light that, when activated, 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.
When a traffic signal that is part of a coordinated corridor of traffic signals is “preempted” by an emergency vehicle, that preemption disrupts the coordination. It can take up to three cycles of each traffic signal (5-6 minutes) for that intersection to get back “in step” with the coordination plan.
Q. Why do some traffic signals flash at night?
At the request of several community groups in Highlands Ranch, Douglas County Traffic conducted a study to develop a policy regarding flashing traffic signals at night and determine if certain signals met those requirements. Eligibility for flashing traffic signals at night was based on nighttime traffic volumes, accident history, and proximity to bars and other drinking establishments. As a policy, all traffic signals which are set to flash overnight will flash from 11:30 pm to 5:00 am. Traffic signals in flash will flash yellow for major street traffic and red for minor street traffic. This type of operation allows traffic from the side-street to take advantage of the lack of significant traffic on the major street – additionally, major street traffic need not wait at a red light just because one vehicle caused the traffic signal to cycle.
Q. Is it possible for two conflicting directions of traffic at a signalized intersection to receive green lights at the same time?
It is actually not possible for two conflicting movements of traffic to have green and/or yellow lights at the same time. There are a number of safety features that prevent this exact condition from occurring. Even if a number of these features were to fail and the controller of the intersection were to try to have conflicting movements green at the same time, there is another piece of equipment called a “conflict monitor” that is designed specifically to detect and prevent this from occurring. If the conflict monitor “sees” a potential conflict, it puts the entire intersection into flashing operation, and the intersection will stay that way until a technician has been able to fix the problem.
As everyone knows, a yellow light appears after a green light. When a particular movement goes from yellow to red, the entire intersection remains red for a selected amount of time (usually 1-2 seconds) before the next movement receives a green light. This also allows any vehicles that entered the intersection on a yellow (not red) light to safely clear the intersection before the next vehicles receive a green light to proceed. This is a software feature in addition to the hardware features described above.
Occasionally, an oversized vehicle can damage an overhead traffic signal light or, in the case of an accident or loss of control, may otherwise impact a traffic signal light mounted on a pole. In some cases the light, although not otherwise damaged, may be rotated by such an event to the point that it is visible to the wrong direction of traffic. This is a repair that needs immediate attention. We appreciate any reports of damaged traffic signal equipment, since it is impossible to actively monitor each signalized intersection on a continuous basis. If you do know of any traffic signal indications that may be rotated or are otherwise incorrectly mounted, please call Douglas County Traffic at 303.660.7490 or email a detailed description of the problem to traffic@douglas.co.us.
Q. What are the Douglas County Traffic Management Centers used for?
There are three Traffic Management Centers (TMCs): a primary TMC and two satellite TMCs. At each TMC, there are different capabilities available to Traffic personnel. All of the TMCs have the ability to view the County’s closed circuit television (CCTV) traffic surveillance cameras. Additional features include the ability to communicate with the traffic signals to perform various maintenance duties or to upload/download signal timing plans.
- The primary TMC, located at the Park Meadows Center at 9350 Heritage Hills Circle in Lone Tree, has the most functionality of all the TMCs. There are currently 10 monitors ranging in size from 20” to 40” available for viewing Traffic’s CCTV camera images. The Park Meadows TMC has the highest level of communication abilities with our traffic signals, as it is the junction of several key fiber optic communication corridors used by Douglas County Traffic. This TMC is also able to view CCTV feeds from CDOT as well as other local jurisdictions. The County’s permanent variable message signs (VMSs) are controlled from the TMC. Some of the video detection systems are also monitored from the Park Meadows TMC. System Detectors send traffic congestion data to the TMC. The Park Meadows TMC is staffed Monday through Friday, 6-9 AM and 3-6 PM (Except Holidays) for the purpose of monitoring the Traffic cameras. TMC operators also monitor the equipment to ensure it is in optimal operational condition. In the event of a major incident affecting traffic, a major traffic signal malfunction, or a power outage affecting traffic signals, the TMC Operators will serve as the communication hub coordinating activities. The Operator will have the ability to provide valuable information to the First Responder or Traffic Maintenance Staff.
- The first satellite TMC, located at the Traffic Services shops at 3080 N Industrial Way, in Castle Rock has CCTV viewing and control capability as well as traffic signal communications capability.
- The second satellite TMC is located in the Engineering Administration offices of the Phillip S. Miller Building at 100 Third Street in Castle Rock. Currently at the Phillip S. Miller TMC only control and viewing of Traffic’s CCTV camera images is possible
The purpose of the TMCs is to communicate with the traffic signals and other traffic devices located along the County roadway network. Through the visual confirmation of problems using the traffic surveillance camera images, Douglas County Traffic staff can plan what equipment to bring to the location where problems have been identified. Additionally, using the remote communications, maintenance staff can diagnose, and perhaps even fix, a problem without leaving the office. All this works toward Douglas County’s goal to provide excellent service to the public.
Q. What happens to Douglas County traffic signals when they lose power?
It depends. Typically the signal will go “dark”. However, some of our existing traffic signals have a battery back-up system (Uninterruptible Power Supply – UPS) that can maintain either normal or flash operation of the traffic signal. Typically the UPS is capable of maintaining power for only a few hours. It is still crucial to remember that if the traffic signals do go “dark”, Colorado State Law (Colorado Revised Statute §42-4-612 or Colorado Model Traffic Code §612) dictates that motorists shall treat the intersection as an all-way stop sign, unless an officer is directing traffic. (New traffic signals that have not yet been turned on have bags over the signal indications so that they are not confused with a traffic signal that has lost power. Motorists should continue to use the visible traffic control devices – stop signs, etc – if present.)
Q. Can I learn more about what Douglas County Traffic does? Can I see how traffic signals work in person?
Yes! If you e-mail or contact us at 303.660.7490, Douglas County would be happy to arrange a tour of our facilities for individuals or small groups (such as HOA Boards, Scout troops, school classes, etc.). We will show you how traffic signals work using our test bench in our shop where we typically have a working traffic signal controller to demonstrate.