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Traffic Engineering

Frequently Asked Questions

“How does a signal operate? Is a specific signal operating correctly?”

There are many different types of traffic signals. Some are fixed-time and each movement gets a preset amount of time. Some use detectors buried in the pavement and time is allocated based on the amount of vehicles sensed by these detectors. At other intersections, some movements have detectors and other movements do not. At some intersections, where possible, the pedestrian movement is automatically recalled each cycle. At others pedestrians must push a button to bring up the walk signal. The proper operation of signals can be checked remotely by computer, or in the field by traffic signal personnel. Those with specific questions about signal operations should contact the Traffic Department at 343-8425.

“Why do I have to stop? Why are signals so poorly synchronized?”

Intersection signals are coordinated, or synchronized with each other to reduce stops and delay for the major traffic movements. Coordinating signals require that all signals be programmed with a common cycle length, which is the amount of time it takes a signal to sequence through all traffic movements one time. The quality of movement through a series of traffic signals depends on the spacing between signals, the speed of traffic, the cycle length, and the amount of traffic. Signals along main arterials are generally coordinated with each other during the day, when there are heavy traffic flows. It is often not possible to progress traffic in both directions because of poor spacing between traffic signals. Sometimes it is necessary to choose one direction to progress. When two-way progression is not possible, the Municipality often uses computerized traffic modeling to find coordinated timing plans that decrease the total delay and stops for all users of the system. Traffic turning onto of off of a side street is generally not progressed, and turning vehicles can usually expect to stop at the next signal. Specific questions about signal progression should be referred to the Traffic Department at 343-8425.

“Why do I have to wait so long after I stop at a specific signal?”

At most traffic signals several different timing plans are used throughout the day to account for varying levels of traffic demand. The length of the wait depends on the signal cycle length and amount of traffic. In general, a longer cycle length increases the amount of vehicles that can be moved through an intersection (capacity). Increasing cycle lengths also increases driver delay. Cycle lengths range from 60 seconds to 160 seconds in the Municipality, depending on the size of the intersections and the amount of traffic. Cycle lengths must be longer at larger intersections to serve the greater number of separate traffic movements during the timing sequence, to accommodate much longer pedestrian crossing times, and to accommodate higher volumes of traffic. Requests for timing changes at individual intersections should be referred to the Traffic Department. Information needed for a signal employee to investigate a requested timing change is what day of the week and what time of day a problem occurs. Call the Traffic Department at 343-8425.

“Why isn’t there enough green time to get the traffic through the signal for a specific movement?”

The amount of green time programmed for each movement at a signal varies by time of day. Sometimes there is more traffic at a signal than the signal can handle, and the signal is over its capacity. In these situations, the Traffic Department attempts to time the signals to equalize delays for conflicting movements. At other times green time can be moved from one movement to a conflicting movement, realizing that improving one movement hurts another. Increasing green for one movement requires decreasing the amount of green time for another movement.

Requests for timing changes at individual intersections should be referred to the Traffic Department. Here, too, information needed for a signal employee to investigate a requested change is what day of the week and at what time of day a problem occurs. Call the Traffic Department at 343-8425.

“How do I get a new signal installed?”

Installing a new traffic signal first requires determining if a signal is needed. If a signal is needed, then a method of funding and constructing the signal must be found. Evaluating the need for a traffic signal requires careful analysis of the accident history, the intersection geometry, and amount of traffic. The number of traffic accidents almost always increases when a signal is installed, as interruption of free flow results in an increased number of rear-end type accidents. Certain types of accidents that tend to be more severe can often be reduced by installing a signal. The analyst must weigh the different types of accidents and compare them to federal guidelines. There are certain federal requirements that must be met before a signal can be installed.

If a signal is needed, the next challenge is to find a method of constructing and funding the signal. On municipal roadways, signals can be included in road improvement projects, and constructed if bonds are approved by the voters. However, most of the major roads are owned by the State of Alaska, and Municipal funds cannot be spent on these roadways. If a signal is needed on a state-owned roadway, other methods of funding must be sought, such as requesting inclusion in the state safety improvement program.

A new signal usually costs more than $250,000 to construct, and then additional dollars will be needed for annual maintenance. With limited funding, desired new signals must be compared with intersections with the worst accident problems, which receive priority. Requests for new traffic signals can be referred to the Traffic Department at 343-8425.

”How do I find how much traffic there is at a specific location, or how many accidents there have been?”

The Traffic Department counts traffic at all major intersections in the Municipality once every three years. Traffic at smaller intersections will be counted as needed, due to special projects or investigations. These counts are stored in a database that is maintained by the Traffic Department. All intersection related accidents for which police respond or accident reports are filled out, are also tracked and summarized in a computer database. This allows the Municipality to identify safety problems that arise at specific intersections. Requests for traffic volume or accident data should be submitted to the Traffic Department at 343-8406.

“How do I find how a signal was operating at a specific time and date, and if it was operating correctly?”

The Traffic Department cannot say exactly how a signal was operating on a specific date and time due to field variables such as traffic demand. However, we can determine how a signal was programmed to operate, and if there were any malfunctions such as burned out light bulb or power outage on a specific date.

Records of all programming changes and all maintenance responses are maintained at the Traffic Department. Requests for historical records concerning traffic operations should be referred to the Traffic Department at 343-8425. Sifting through the records takes a significant amount of research, and it is not a good idea to make a request a week before the court date. A thorough records search can take up to three weeks.

“How does a pedestrian signal work?”

Where possible, pedestrian signals are programmed to automatically be served each signal cycle, so that pedestrians do not have to push the pedestrian button. This is often not possible due to site-specific constraints, and it is a good idea to push the button if there is one available.

Once a pedestrian indication starts, there can be some confusion as to the meaning of the signal indications. The first indication is a white walking man. This symbol means the pedestrian can start walking in the direction of the signal. This is followed by a flashing orange hand symbol. The flashing hand does not mean that the pedestrian should stop crossing the street. When this symbol is shown, any pedestrians who have started to cross the street should continue crossing, but pedestrians that have not yet started to cross should not begin crossing.

The length of the flashing indication can be quite long. It is calculated based on the length of the crosswalk and the nationally recognized average walking speed of pedestrians. A flashing hand terminates with a solid orange hand symbol. Pedestrians should not be in the crosswalk when this symbol is being shown. Questions about pedestrian signals should be referred to the Traffic Department at 343-8425.

"Are Stop sign effective as a tool for speed control?"

No. Stop signs can have the opposite effect on speeds. We found speeds tend to increase within as little as 150 to 300 feet from the stop sign. Drivers try to make up for what they consider lost time.  

    • Traffic Engineering
    • Municipal Traffic Engineer: Stephanie Mormilo
    • 4700 Elmore Road, Anchorage, AK 99507
    • 907 343-8406