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Traffic Frequently Asked Questions

Douglas County Traffic receives numerous inquiries about our traffic signal system, speed limits, neighborhood traffic issues, requests for traffic volume data, etc. Many of these questions can be addressed in a frequently asked question (FAQ) format. Most questions of a general nature are answered below.

Who regulates traffic in Douglas County?
Who builds and maintains traffic signals in Douglas County?
How do traffic signals work?
Who maintains flashing school zone beacons?
How is it decided if a traffic signal should be installed and won’t a signal reduce accidents at an intersection?
What are the cameras at traffic signals for?
Are traffic signals in Douglas County coordinated to reduce or eliminate the need to stop at red lights?
Once I turn onto a street where the traffic signals are coordinated, I shouldn’t have to stop, right?
Do any traffic signals not run in coordination with other traffic signals?
Why do green left turn arrows appear at different times during different times of the day?
How do signals for pedestrians work?
Why do I have to wait so long to get a green light or a WALK signal?
Why can’t we have a stop sign in our neighborhood to reduce accidents?
What are traffic control zones and how should I react?  
Why not lower the speed limit to reduce hazards in our area? 
Why can’t we use speed bumps on our block?
Won’t a “Children at Play” sign help protect our children?
Do emergency vehicles get priority at signalized intersections in Douglas County?
Why do some traffic signals flash at night?
Is it possible for two conflicting directions of traffic at a signalized intersection to receive green lights at the same time?
What happens to Douglas County traffic signals when they lose power?
Can I learn more about what Douglas County Traffic does?  Can I see how traffic signals work in person?


Who regulates traffic in Douglas County?
The Traffic Engineering and Operations Division maintains traffic control devices, regulates traffic and studies and analyzes traffic flow to ensure safety and efficiency, and follows the Manual on Uniform Traffic Control Devices (MUTCD) to determine the appropriate use of traffic devices. These guidelines require certain criteria to be met before Traffic Engineering and Operations can use a particular device, as well as ensure that motorists have consistency among different communities throughout the country.

Who builds and maintains 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, operates or maintains various intersections, please refer to the Signalized Intersection List.

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 Broadway/C-470, 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.

How do traffic signals work?
Pre-timed and traffic-actuated signals are the two types used on today’s roads. Pre-timed controllers operate on a regularly repeated sequence of signals and are used where traffic volume is stable and predictable. Traffic-actuated controllers change in response to traffic demand and are generally used where traffic volume fluctuates widely, and where interruptions to major street flow must be minimized.

Who maintains flashing school zone beacons?
The school zone beacons on roads within unincorporated Douglas County are maintained by Douglas County Traffic Engineering and Operations.  They are set to turn on for the school’s start and release times (including kindergarten – midday). Traffic staff confirms start/release times by contacting each school individually on an annual basis.  lease report malfunctions to Traffic Engineering at 303.660.7490 or  traffic@douglas.co.us 

How is it decided if a traffic signal should be installed and won’t a signal reduce accidents at an intersection?
Traffic engineers are required by state law to compare each situation with national standards established by studying intersections throughout the country. The Manual on Uniform 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.

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 generally reduce the number of right-angle collisions, the number of rear-end and pedestrian accidents may actually increase.

What are the cameras at traffic signals for?
Douglas County uses a couple of different types of cameras at signalized intersections:

Intersection Detection Cameras– These cameras use video technology to detect when a vehicle is approaching a signalized intersection and 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.

Closed Circuit Television (CCTV) CamerasThese 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 during peak travel periods or when an accident occurs. The cameras can be viewed on monitors at the Traffic Management Center.

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:  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, and number of lanes available for each movement of traffic.

Most of Douglas County’s traffic signals operate on three different timing plans, which include AM Peak plan, Mondays to Fridays; PM Peak plan, Mondays to Fridays; and 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.

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 pre-emption, and the frequency of pedestrians (having pushed the button to cross) each cycle.

Once I turn onto a street where the traffic signals are coordinated, I shouldn’t have to stop, right?
Not necessarily, the 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 traffic. At some locations, it is necessary to 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.

Do any traffic signals not run in coordination with other traffic signals?
Yes, that type of operation is referred to as actuateddemand-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 distance to adjacent traffic signals, the volume of traffic, availability of video detection and other “odd” conditions like the presence of unique traffic generators (eg. schools, large church, etc) on the side street.

Why do green left-turn arrows appear at different times during different times of the day?
Traditionally, green arrows for left-turning 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 a “lagging” left turn 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.

How do signals for pedestrians work?
When a pedestrian pushes the button on the signal pole, a pulse 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 if safe to do so. 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 based on national standards. 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 indications, which display for pedestrians the exact number of seconds remaining before the pedestrian needs to be clear of the intersection.

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.  However, if you 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 to contact the appropriate jurisdiction.

  • 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 predetermined 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 wait times 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 adequate time for them to safely travel through the intersection.

Why can’t we have a stop sign in our neighborhood to reduce accidents?
Installing an unnecessary stop sign as a “nuisance” or “speed breaker” may actually increase the number of accidents in the area. The unwarranted signs breed disrespect by motorists who tend to ignore the signs or slow down without stopping. Impatient drivers view the additional delay as “lost time” to be made up by driving faster between signs.

What are traffic control zones and how should I react?
Whenever construction is in progress on or near the roadway, drivers face rapidly changing traffic conditions. These changes can be hazardous for drivers, workers and pedestrians unless protective measures are taken.  Traffic control zones are divided into several areas to increase safety for both workers and motorists. The areas include: Advance Warning Area – tells motorist what to expect, Transition Area – moves traffic out of its normal area, Buffer Area – provides protection for traffic and workers, Work Area and Termination Area – lets traffic resume normal driving.  When traveling through these control areas, always be alert for workers and decrease your speed to increase safety.

Why not lower the speed limit to reduce hazards in our area?
There is a common misconception that posting a speed limit will influence drivers to drive that speed. The facts indicate otherwise. Studies show that a driver’s speed is influenced more by the appearance of the road and the prevailing conditions than it is by posted speed limits and, in fact, unrealistically low speeds can actually cause accidents.

Why can’t we use speed bumps on our block?
When posted speed limits fail to slow cars down in residential neighborhoods, people often request that speed bumps be installed in streets. However, speed bumps can cause more problems than they solve such as being a hazard to the unwary, disruption for emergency and maintenance vehicles and the cause of an undesirable increase in noise.  In addition, tests show that speed bumps are ineffective in controlling all types of vehicles. The driver of a softsprung sedan is encouraged to increase speed for a better ride over a speed bump, while other drivers may lose control at the same speed.  For these and other reasons, Douglas County rejects the use of speed bumps as standard traffic control devices on public streets.  The control of speeding in residential neighborhoods is a widespread concern that requires persistent law enforcement efforts…not speed bumps.

Won’t a “Children at Play” sign help protect our children?
Studies show no evidence that these signs prevent injury or decrease the speed of vehicles. They can give parents a false sense of security and since nearly every residential block has children living on it, there would have to be signed on each one. Blocks with no signs might imply that no children live there, so the driver does not have to watch out. Children could misinterpret the sign to mean that it is okay to play in the street.  To address pedestrian safety, specific warning signs for school zones, pedestrian crossings, playgrounds, and other recreational areas are used where clearly justified. 

Do emergency vehicles get priority at signalized intersections in Douglas County?
Emergency vehicles 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.

Why do some traffic signals flash at night?
At the request of several community groups in Highlands Ranch,  Traffic Engineering and Operations 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 p.m. to 5:00 a.m.  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.

Is it possible for two conflicting directions of traffic at a signalized intersection to receive green lights at the same time?
There are a number of safety features that prevent this exact condition from occurring.  If a number of these features were to fail and the controller of the intersection was 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.

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. Traffic Engineering and Operations appreciate reports of damaged traffic signal equipment since it is impossible to actively monitor each signalized intersection on a continuous basis. To report a traffic signal that may need to be rotated or is otherwise incorrectly mounted, please call 303.660.7490 or email a detailed description of the problem to traffic@douglas.co.us 

What happens to Douglas County traffic signals when they lose power?
 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 haven’t 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.)

Can I learn more about what Douglas County Traffic does?  Can I see how traffic signals work in person?
Yes, please contact us at 303.660.7490, and we would be happy to arrange a tour of our facilities for individuals or small groups (such as HOA Boards, Scout troops, school classes, etc.). Traffic Engineering and Operations staff 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.