Traffic Signals

Traffic Signals and Signage

The Department of Public Works maintains all aspects of traffic signals from changing bulbs to resetting the timing. If you notice a malfunctioning traffic signal, contact the  Traffic Department to report it to Public Works for inspection and repair. Street signs are constantly being updated. Public Works repairs/replaces signs, as needed, due to accidents and/or weather. If you notice a problem with a traffic sign such as tree limbs in the way, graffiti, a missing sign, etc., contact the  Traffic Department to report it to Public Works for inspection and repair. The Streets Division installs all new signage at the request of the Traffic Coordinating Board. Parking meters are also installed and maintained throughout the downtown area of the city’s business district.

Many of the City’s traffic signals are coordinated to allow for more efficient movement of traffic. The goal of signal coordination is to get the greatest number of vehicles through a corridor with the fewest stops in the safest and most efficient manner. It would be ideal if every vehicle entering a corridor could proceed without stopping. This is not possible, even in the most well designed system.
Signal coordination is the synchronization of two or more intersections along a section of roadway and is a technique that is used to improve overall intersection operations usually quantified as reduction in overall intersection delay.

Coordinating traffic

signals involves connecting them so they work together to provide motorists with green lights as they progress down the street. The traffic on the major street forms into “platoons” of cars that pass through the intersections when the signals at those intersections are green.

Signal coordination is utilized to improve capacity of the existing street system by reducing delays and stops. Furthermore, coordination tends to reduce accidents. Optimizing the timing of coordinated signal systems in order to provide smooth, continuous platoon progression is regarded as one of the most cost-effective traffic management actions through reduction in stops, delays, fuel consumption and exhaust emissions.

This sounds like a simple task to accomplish. With a one-way street and few arterial cross-streets, it is simple. But the following complications can make the calculations become quite difficult:

  • →A two-way street
  • →Arterial cross-streets close together
  • →A route that turns
  • →Left-turn signals
  • →Short blocks

Signal progression for optimized systems face the dilemma of competing goals of minimizing delay, maximizing capacity, and providing good progression to avoid complaints about poor signal timing from the public.

The higher volume roadway is favored over the side street when traffic signals are coordinated. In this situation, side-street traffic may experience an increase in number of stops and/or longer stops. However, the benefit gained by traffic on the higher volume roadway exceeds the degradation in operations experienced by the side-street traffic and overall intersection operations are improved. In simple terms: the majority rules.

Signal coordination provides a means by which the sequence (begin and end) of green lights is established along a series of traffic signals to allow for the uninterrupted flow of traffic between these traffic signals. Signal coordination is most typically used along heavily traveled arterial streets with a frequent presence of traffic signals.

The goal of signal coordination is to get the greatest number of vehicles through a corridor with the fewest stops in the safest and most efficient manner. It would be ideal if every vehicle entering a corridor could proceed without stopping. This is not possible, even in the most well designed system. Therefore, with signal coordination, the heaviest traffic movements are given precedence over the smaller traffic movements.

Benefits of Signal Coordination

  • →Reduces overall stops and travel delays.
  • →Allows for large groups of vehicles to efficiently flow through a series of traffic signals without stopping.
  • →Reduction in the number of stops reduces vehicle emissions and thus improves air quality. Most of the vehicle emissions occur during acceleration (stop and go traffic).

Disadvantages of Signal Coordination

  • →Side street traffic typically experiences a longer wait time.

In the development of signal coordination, we have to manage the competing interests of providing continuous flow of traffic on the arterials, providing adequate time for pedestrians to cross the street, and minimizing the wait time for side street traffic.

Limitations of Signal Coordination
As we strive to improve signal progression and coordination within the City of Elmira, it is important that the public understand the limitations of signal coordination. While traffic signal coordination can reduce stops and travel delays along a particular corridor, travel along a particular street may not completely experience non-stop free-flow conditions due to the following conditions:

  • →Capacity issues as a result of increased traffic caused by growth
  • →Complexity of the street system.
  • →Equipment malfunction
  • →Street construction
  • →Traffic incident

Drive the speed limit. Signals are timed to work best when traffic goes the speed limit. Driving faster will simply get you to the next signal too early, causing you to stop more often. The best way to avoid stopping is to slow down when you see a red light ahead and give it time to change to green.
Stop behind stop bars at red lights. Many intersections have vehicle detectors (wire loops) embedded in the pavement. These signals can detect the presence of vehicles and let the controller know that vehicles are waiting. Stopping behind the bar insures that the controller “senses” your car and keeps the crosswalk clear for pedestrians.

Frequently Asked Questions about Traffic Signal Progression

Coordinated traffic signals provide the following benefits to motorists:

  • →Delay experienced by motorists waiting at signals is reduced.
  • →The number of stops experienced by motorists is reduced
  • →Motorists are grouped in platoons traveling at equal speeds.
  • →There are fewer rear-end accidents because motorists are stopped less often on major streets.
  • →There are fewer right-angle accidents because there is less red light running.
  • →There is less traffic cutting through neighborhoods to avoid signals.

It is impossible to time the signals so that no driver hits a red light.

  • →If you are hitting a number of lights on red, you may be driving too fast since the signals are timed for motorists traveling near the speed limit.
  • →If signals are spaced closely together, it is difficult to achieve progression.
  • →When traffic is very heavy such as driving during rush hour, the signals are timed for the peak direction of travel. If you are traveling against the peak, you may hit more red lights.
  • →If you turn onto a major street, you may hit a red light or two before you get into the “green band” and find yourself in synchronization with the timing plans.

The traffic signals are coordinated to help traffic flow through a series of signals and avoid stops. This is called signal progression.

Ideally, Traffic Signal Progression (“timed” signals) is a process by which the signals along major roads are programmed to permit cars traveling at the posted speed to travel uninterrupted through a series of green lights. Signal progression has been used in major cities across the United States for decades.

While major roads are already programmed for signal progression, there are factors that undermine the success of such a system, including accidents, an excessive number of intersecting driveways between lights, gridlock (back-ups that block an intersection) and interruptions due to heavy pedestrian signal use. In addition, drivers who speed, change lanes too frequently or drive too slowly will arrive at the next signal too early or too late, and will disrupt the signal progression for other drivers.

The major disadvantage of programmed signal technology is that it lacks flexibility – it can’t sense road conditions and adapt accordingly. In the event of a car accident, signal timing can’t detect an accident or expedite the delivery of emergency or law enforcement services, nor can signals on timers advise motorists about alternative routes or adjust timing to correct delays.

On two-way streets, coordination is much more complex. Three variables must be taken into account: 1) the distance between traffic signals, 2) the cycle length, and 3) the speed of travel. Nonstop traffic flow can only be provided where exact relationships exist between these three variables.

Some stops are simply unavoidable with the street system. For example, not all signals are uniformly spaced. Different intersections have different traffic demands, so cycle lengths must vary. And we must keep traffic at or near the speed limit.

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 City 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 or off of a side street is generally not progressed, and turning vehicles can usually expect to stop at the next signal.

There are many issues that may affect the coordination of traffic signals. It is easy to coordinate signals that are on one-way streets to provide for very efficient movement of traffic. That is why you will see one-way streets in many downtown areas – it is the most efficient way to move large amounts of traffic with relatively few lanes. Coordinating signals on two-way streets where the signals are irregularly spaced is a much more difficult challenge. In some cases, it becomes physically impossible to provide good coordination simply due to the spacing of the intersections and the speed that people are driving.

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 90 seconds, 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.

Signals that are in a coordinated mode are confined to a cycle length, which is governed by the cycle of a nearby major intersection. All signals along an arterial must have a common cycle length in order to achieve progression. Within that cycle length, a block of time is allocated to each movement. Each movement can appear only at a certain point in the cycle; once that has occurred, the movement cannot appear again until the next cycle. If a movement does not need all of its allocated time, the unused time becomes available to the next movement; this continues until all of the unused time, if any remains, ultimately is inherited by the main street movement where the cycle “zeros” itself out or begins again. Cycle lengths vary depending on the time of day. During the AM and PM rush hours, signals have their longest cycle lengths because the major roads must accommodate the greatest amount of traffic. In the midday the cycle lengths are slightly shorter and the shortest cycles typically occur at night and on weekends.

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 signals are timed 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.