Traffic signal synchronization systems

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Traffic signal synchronization systems seek to promote more efficient automobile travel by timing traffic signals to allow for vehicles to traverse the most intersections in the shortest possible amount of time, thereby minimizing congestion and delays.[1] Synchronized traffic signals are designed to turn green just as a cluster of vehicles is approaching. [1] Conversely, the signal is typically red when there are few or no cars approaching it. Traffic signal synchronization can take a variety of forms. While some areas use synchronization at all times of the day, other areas have chosen to implement this policy only during the daytime since lower traffic volumes at night make synchronization ineffective. [2] Additionally, the degree of cooperation between municipalities who use synchronization remains variable. Although some municipalities have cooperated to align their synchronization systems with one another, it is common for vehicles to encounter delays while crossing municipal boundaries due to uncoordinated synchronization systems. [3] The implementation of traffic signal synchronization also varies based on the degree to which it is utilized by a specific municipality. While some areas such as Los Angeles have synchronized all of their traffic signals, other areas have synchronized only a portion of their signals due to budgetary constraints or light traffic. [4] Traffic signal synchronization has several benefits such as shorter travel times, less money spent on gasoline, and less pollution from idling vehicles. [5] Additional benefits include improvements to the local economy, a reduction in aggressive driving, and a reduction in the need for widening and new construction. [5]



Conceptual Example

A town seeks to reduce congestion on its roads but is worried about the environmental and financial drawbacks of widening roads or building new roads. The town realizes that its economy could be negatively affected by congestion since people are less likely to fight traffic to travel to stores and tourists are less likely to visit the town. Furthermore, citizens are growing increasingly concerned about the poor air quality associated with idling vehicles at red stop lights. The town sees traffic signal synchronization as an option that will correct these problems. After approving the measure and allocating funding, the town implements traffic signal synchronization on its busiest road. As more funding becomes available and as the town has had time to study the possible effects of synchronization on different road networks, it invests additional money in synchronizing other roads. The town eventually reaches its goal of synchronizing all traffic signals on roads that have sufficient traffic to warrant this technology. As a result of traffic signal synchronization, air pollution and average travel time in the town has decreased, while economic activity and consumer satisfaction with the transportation system have increased. The town also has additional revenue to spend on other municipal projects.

Specific Example

Los Angeles has long been notorious for traffic congestion and delays. However, in recent years, the city has been using traffic signal synchronization as a means of mitigating these problems. Los Angeles’s automated traffic control and surveillance system, begun in anticipation of the 1984 Olympics, was undertaken with the goal of synchronizing all of Los Angeles’s stop lights.[6] This goal was met in 2013 after a cost of approximately 400 million dollars.[6] All of Los Angeles’s 4,500 traffic signals are synchronized, an accomplishment unmatched by any other major city in the world. [4] According to the Los Angeles Transportation Department, these improvements have increased the average speed of traffic in Los Angeles from 15 to 17.3 miles per hour.[4] Unlike other synchronization systems, which operate on fixed cycles, Los Angeles uses sensors to send traffic volume data to a central computer system located underneath the city.[4] The data is then analyzed by special software and traffic signals are changed accordingly. [4] Among the other advantages of the system is that transit services such as light rail are given priority at intersections.[7] Furthermore, the system can also respond to pedestrians and cyclists who are waiting to cross an intersection.[6]


Tradeoffs.png Note that some of the tradeoffs of traffic signal synchronization systems are similar to those of car speed synchronization systems. Tradeoffs of implementing this policy may include:

  1. Synchronized signals require reassessment every few years or whenever a new stoplight is installed and this process can be expensive. [5]
  2. Synchronized traffic signals could cause people to drive faster, negatively affecting safety. (Note that this is at odds with the goal of reducing the rate of injuries and deaths from automobile transportation.)
  3. Less congestion and faster travel times could cause more people to drive instead of walk, bike, or take transit, making it difficult to reduce pollution and sustain the improved travel times (Jevons Paradox).[4]
  4. Less congestion could make municipalities less willing to invest in other forms of transit such as rail or bus service.
  5. Less congestion and faster travel times could encourage people to live farther away from work, thus facilitating sprawl.
  6. Connector roads could become more congested as a result of improvements to traffic flow on arterial roads.
  7. The maintenance costs for the road might increase due to higher traffic volumes.

Compatibility Assessment

Compatibility Assessment.png If answered yes, the following questions indicate superior conditions under which the policy is more likely to be appropriate:

  1. Does the municipality have the funds and the resources to implement traffic signal synchronization and conduct reassessments on a frequent basis?
  2. Does the municipal government have the authority to implement the policy?
  3. Does the community have enough traffic to warrant traffic signal synchronization? [2]
  4. Has the community conducted extensive studies on how traffic signal synchronization will affect traffic patterns and where the best places to implement synchronization are?
  5. Will staff be available to intervene if the system malfunctions or if there is a sudden change to traffic flow?
  6. Would traffic signal synchronization be easier to implement or more effective at reducing congestion, delays, and pollution than other measures such as car speed synchronization?
  7. Will the municipality have measures in place to ensure that speeding does not become a problem in the absence of the traffic calming effects of frequent red lights?



Assuming that a jurisdiction has decided to adopt the policy, the following questions will need to be answered when determining how to implement this policy:

  1. How should the system be designed to accommodate walkers and bikers, if at all?
    1. Synchronization tends to increase the speed of cars, which makes conditions more dangerous for walkers and bikers and makes them less willing to walk or bike.
    2. Bicyclists usually don’t arrive at an intersection at the same time that the clusters of cars do, so it can be difficult to program traffic signals to accommodate this mode of travel.
    3. Some people would argue that the goal of traffic signal synchronization is to reduce congestion from cars, so it could be difficult to convince people of the need to accommodate bicyclists and pedestrians at these intersections.
  2. How do communities decide where synchronization can be effectively implemented?
    1. On roads where traffic volumes are low, synchronization devices can increase travel time. In these situations it is better for each signal to operate on an independent cycle.[2]
    2. Many studies indicate that synchronization is also ineffective on highly-congested roads. [8]
    3. Synchronization is typically best implemented on roads that include frequent traffic signals and have moderately high traffic volumes.
  3. How do communities decide when synchronization can be effectively implemented?
    1. Irvine, California only implements traffic signal synchronization between 6:00 AM and 8:00 PM. At night, when traffic volumes are lower, the signals revert to a traffic-actuated mode and operate in response to the traffic at that specific intersection, as opposed to the surrounding traffic signals.[2]
  4. What will the cycle length of the light be?
    1. High-traffic roads should have a green light for a longer period of time than lower-traffic roads.
    2. A typical busy street might have a 120 second cycle, 90 seconds of which will give a green signal to traffic on the main road. [2]
    3. On less busy roads, the cycle length may be longer with a greater proportion of the cycle being devoted to left turns and crossing traffic. [2]
    4. Cycle lengths often change based on the time of day. For example, the green light will last longer on arterial routes during rush hour. [2]
  5. Where will the funding for traffic signal synchronization come from?
    1. Many localities fund their own traffic signal synchronization programs, but the Federal Highway Administration can also provide funding. [5] [3]
    2. If the project is locally-funded, the municipality is usually able to recoup its investment quickly since commerce and economic development can often be improved through better traffic flow. [4]
      1. Los Angeles spent 400 million dollars over 30 years on synchronization, yet it saves citizens 1.3 billion dollars per year in terms of gasoline and time-savings.[4]









  • Advocates - Mass Transportation Assumption: Traffic signal synchronization makes driving easier, cheaper, and more efficient, which may lead more people to drive instead of take transit.
  • Advocates - Smart Growth Assumption: Traffic signal synchronization makes it easier for people to live far away from work, thus facilitating sprawl.
  • Advocates - Alternative Energy. Assumption: The increased fuel efficiency associated with traffic signal synchronization may give people less incentive to support alternative energy.
  • Advocates - Bicycle Safety. Assumption: Faster traffic makes conditions less safe for cyclists.
  • Advocates - Bicycle Transportation. Assumption: Cyclists may feel less comfortable cycling due to the faster speed of traffic. Additionally, synchronized traffic signals are not timed for the speed of cyclists, which means they will frequently have to wait at red lights.
  • Advocates - Pedestrian Safety. Pedestrians seeking to cross the road will have to contend with higher traffic speeds.
  • Advocates - Pedestrian Transportation. Pedestrians seeking to cross the road will have to contend with higher traffic speeds.
  • Advocates - Pedestrian Transportation. Pedestrians seeking to cross the road will have to contend with higher traffic speeds.




  • Shinar, David, Muki Bouria, and Liat Kaufman. “Synchronization of Traffic Signals as a Means of Reducing Red Light Running.” Human Factors 46, no. 2 (Summer 2004): 367-72. PubMed. Accessed October 16, 2016. This article describes a study that found that traffic signal synchronization reduces red light-running, thereby reducing accidents.
  • Hu, Xiaojian, Jian Lu, WeiWang, and Ye Zhirui. “Traffic Signal Synchronization in the Saturated High-Density Grid Road Network.” Computational Intelligence and Neuroscience (2015): 1-11. PubMed. Accessed October 16, 2016. This article proposes an alternative form of traffic signal synchronization which is more effective on heavily-congested roads.
  • Huang, Ding-wei, and Wei-neng Huang . “Traffic Signal Synchronization.” Physical Review E 67 (2003): PubMed. Accessed October 16, 2016. This article explains that traffic signal synchronization is less effective on roads with extreme congestion.
  • De Coensel, B., A. Cana, B. Degraeuwe, I. De Vlieger, D. Botteldooren. “Effects of Traffic Signal Coordination on Noise and Air Pollutant Emissions.” Environmental Modelling & Software 35 (2012): 74-83. Science Direct. Accessed October 16, 2016. This article describes a study which found that traffic signal synchronization reduces carbon dioxide, nitrogen oxides, and particulate matter concentrations. The effect on noise levels is less clear.


  1. 1.0 1.1 1.2 "Traffic Signal Synchronization." City of Irvine. Accessed October 20, 2016.
  2. 2.0 2.1 2.2 2.3 2.4 2.5 2.6 "When Traffic Signal Synchronization is Warranted." City of Irvine. Accessed October 21, 2016.
  3. 3.0 3.1 3.2 "Signal Synchronization. Orange County Transportation Authority. Accessed October 21,2016. Cite error: Invalid <ref> tag; name "Orange_County" defined multiple times with different content
  4. 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 Lovett, Ian. "To Fight Gridlock, Los Angeles Synchronizes Every Red Light." New York Times. April 1, 2013. Accessed October 21, 2016.
  5. 5.00 5.01 5.02 5.03 5.04 5.05 5.06 5.07 5.08 5.09 5.10 Paulson, S. Lawrence. "Managing Traffic Flow Through Signal Timing." Federal Highway Administration. Last modified June 12, 2015. Accessed October 21, 2016.
  6. 6.0 6.1 6.2 "Every L.A. Traffic Signal Now Synced." KCETLink. February 20, 2013. Accessed October 21, 2016.
  7. 7.0 7.1 "Signal Synchronization." LADOT. Accessed October 21, 2016.
  8. Huang, Ding-wei, and Wei-neng Huang . “Traffic Signal Synchronization.” Physical Review E 67 (2003): PubMed. Accessed October 16, 2016.
  9. "Traffic Signal Synchronization." City of Lake Forest. Accessed October 21, 2016.
  10. "Traffic Signal Synchronization." City of Santa Clarita. Accessed October 21, 2016.
  11. "Traffic Signal Synchronization." City of Agoura Hills. Accessed October 21, 2016.
  12. "Traffic Signal Optimization Program." City of Seattle. Accessed October 21, 2016.
  13. "Traffic Signal Synchronization Timeline." City of Buffalo. Accessed October 21, 2016.
  14. "Traffic Signal Synchronization and Management Project." City of Salt Lake City. September, 2011. Accessed October 21, 2016.
  15. Begley, Dug. "Traffic light timing keeps congestion in sync." Houston Chronicle. May 27, 2013. Accessed October 21, 2016.
  16. Danseyar, Susan. "County tests new technology for traffic signals synchronization." Miami Today. June 21, 2016. Accessed October 21, 2016.
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