Traffic Signals

Traffic Signal Standard Drawings

Click to view the March 14, 2007 signal pole design memorandum and traffic signal standard drawings.

Click to go to the Uniform Road Design Standards page.

Roundabouts

A roundabout is a circular intersection with the following characteristics:

• Entering vehicles YIELD to vehicles in the intersection,
• Vehicles travel at slower speeds which increases safe travel through the intersection,
• Traffic circulates counterclockwise through the intersection which reduces conflict and the number of decision points for users.

Click to view the Roundabouts-Another Safe Intersection brochure.

Click to view a YouTube video produced by the county demonstrating the operation of a roundabout.

How the Flashing Yellow Arrow works

The County has been adding flashing or blinking yellow arrows at left turn signals.  When the flashing yellow arrow is displayed, left turns are allowed but drivers must yield to oncoming traffic and pedestrians before making the left turn.

Click to view the Flashing Yellow Arrow brochure.

Click to view a YouTube video produced by the county demonstrating the operation of the Flashing Yellow Arrow.

When traffic signals should be installed 

Traffic signals should be installed when they will alleviate more problems than they will create. This must be determined on the basis of an engineering study. A warranted traffic signal that is properly located and operated may provide for more orderly movement of traffic, and may reduce the occurrence of certain types of accidents. On the other hand, an unwarranted traffic signal can result in increased delay, congestion, and accidents.

Many people seem to believe that traffic signals are the answer to all traffic problems at intersections. If this were true, no traffic engineer in his right mind would deny a request for a signal. However, a traffic signal only functions by stopping traffic, and any time a motor vehicle is stopped in the road an accident potential is created. It does not matter whether the stop is caused by a flat tire, a left turn into a driveway, or by a traffic signal - the possibility exists that a following motorist will not notice the stopped vehicle until it is too late.

What traveler has not experienced that sickening feeling that occurs when a traffic signal suddenly turns amber a few hundred feet in front of them? Who has not experienced the aggravating hopelessness of waiting in a long line of cars for a traffic signal to change, moving ahead a few feet, and then having the signal turn red again? The need for traffic signals should be based on competent engineering study.

How the County decides where to install traffic signals

The County collects all of the relevant data at a location that is being considered for a traffic signal. Once the data are collected, they are compared to standards that have been established by extensive research and experience. Traffic engineers throughout the United States to help determine appropriate signal locations use these standards, called Traffic Signal Warrants. A properly placed signal can improve the flow of traffic and decrease accidents. An unnecessary one can be the source of danger and annoyance to all that use the intersection including pedestrians, bicyclists, and motorists.

The Washington County Traffic Engineering Section wants to ensure that when a traffic signal is installed at a specific location, traffic and pedestrian safety are improved. You may be surprised that traffic signals do not always prevent accidents. Engineering studies have shown that in many instances, accidents increase after a traffic signal is installed. Not only are pedestrians lulled into a false sense of security because of the new signal, but studies have shown that rear-end collisions often increase too.

Traffic signals are a tremendous investment. Therefore, the County must carefully prioritize where and when traffic signals will be installed. When determining whether or not a traffic signal is necessary at a specific location, the Washington County Traffic Engineering Section evaluates and tries to answer several questions:

• How much traffic is there on the intersecting streets?
• Are high levels of traffic consistent throughout the day or just during a few hours?
• Is there a lot of pedestrian traffic?
• Is the street a wide, high speed, and busy thoroughfare?
• Are school children crossing the street?
• Will a signal improve the flow of traffic or cause gridlock with other nearby signals?

A signal may increase the amount of traffic into and out of your neighborhood because a signal often can indicate that the street is a through street even though it may not be. As well, signals cause unnecessary delays to drivers during certain times of the day. This increase in delay increases air pollution. It can also cause driver frustration if there is not much traffic on the major street.

The traffic signal as a traffic control device

Traffic signals should be used only where lesser forms of control have proven ineffective, since signals almost always create more "overall intersection delay." In fact, minor movements may experience excessive delay, particularly if the signal is improperly timed. As a result, many drivers switch to less desirable alternate routes or to residential streets to avoid the added delay.

It is important that the selection and use of this traffic control device be preceded by a thorough study of traffic and roadway conditions and that the determination of the type of control and method of operation be based on the study data.

Traffic signals are electrically operated traffic control devices, which alternately direct traffic to stop and to proceed. The following discussion examines what factors enter into traffic engineers' decisions to install traffic signals. Because there is a common belief that signals are the answer to all traffic problems at intersections, this is offered in the interest of developing broader public understanding about what signals will do and what they won't do.

Advantages of Traffic Signals

Signals offer the maximum degree of control at intersections - they relay messages of both what to do and what not to do. The primary function of any traffic signal is to assign right-of-way to conflicting movements of traffic at an intersection; it does this by permitting conflicting streams of traffic to share the same intersection by means of time separation. By alternately assigning right-of-way to various traffic movements, signals provide for the orderly movement of conflicting flows. They may interrupt extremely heavy flows to permit the crossing of minor movements, which could not otherwise move safely through the intersection. When properly timed, the traffic signal increases the traffic handling capacity of an intersection, and when installed under conditions, which justify its use, it is a valuable device for improving the safety and efficiency of both pedestrian and vehicular traffic. In particular, signals may reduce certain types of accidents, most notably the angle (broadside) collision.

Disadvantages of Traffic Signals

While many people realize that traffic signals can reduce the number of angle collisions at an intersection, few realize that signals can also cause an increase in other types of accidents. It has been well documented that other types of accidents, notably rear-end collisions, usually increase when a signal is installed. Normally, traffic engineers are willing to trade off an increase in rear-end collisions for a decrease in the more severe angle accidents, however when there is no angle accident problem at an intersection, there is nothing to trade off and the installation of traffic signals can actually cause a deterioration in the overall safety at the intersection. This situation sometimes prompts the remark, "You mean you won't do anything until somebody gets killed!" What is not fully understood is that traffic signals are not a "cure-all" and that the primary goal of all traffic engineers is to attain the safest and most efficient traffic flow feasible. In addition to an increase in accident frequency, unjustified traffic signals can also cause excessive delay, disobedience of signals, and diversion of traffic to inadequate alternate routes.

Traffic signals are much more costly than is commonly realized, even though they represent a sound public investment when justified. A modern signal can cost taxpayers between $250,000 and $500,000 to install, depending on the complexity of the intersection and the characteristics of the traffic using it. Of course there is a perpetual cost which is almost never considered - the cost of the electrical power consumed in operating a signalized intersection 24 hours a day. This now averages about $1,500 per year.