What are the city's limits?

April 2, 2018
Traffic control systems can improve safety and mobility, but there are factors to consider

About the author: Stotler is the immediate past president of The International Municipal Signal Association (IMSA) and currently serves as the director of education for IMSA.


The ability to move traffic in an urban environment has been a challenge at best. Initially focused on the movement of motor vehicle traffic with well-established rush hours, the equation to a successful transportation system has been crowded with new safety issues and the need to maintain or even increase mobility. What does this all mean? I'm not sure, but give me a minute or two and I'll try to unfold some of the mystery.

The elements for a safe and efficient urban traffic control system are as varied as any technology out there in use today. From the pre-timed system to the sophisticated system utilizing traffic adaptive software to assure safe traffic flow, there is a system available for most situations.

Whatever the case, the system will only be as good as the information collected and used to design and operate it. Continuous monitoring for changes in traffic demand and volume should be considered during the system's engineering stage of the project. This can be done in several ways.

The adaptive traffic control system depends heavily on input detection to facilitate efficient operation. System input detection, such as inductance loops and an assortment of overhead detectors, allow the system to adapt to the real-time changes in traffic. This type of system works well, but is challenged when dealing with pedestrian traffic.

Another issue to point out is the cost to maintain the input detection the system needs to reach its full potential.

But with that said, adaptive traffic control systems work well in an urban environment, dealing with congestion caused by the unexpected, such as traffic incidents, work zones and special events.

The pre-timed system of old used primarily three cycle lengths, with a signal plan for each of the rush hours (morning and evening peak), and a signal plan for all other times, often called off-peak.

Today's pre-timed systems are much more sophisticated as are the adaptive systems, offering numerous signal plans to accommodate traffic demands. This system tends to be pedestrian friendly as the timings and the frequency of pedestrian movements are consistent.

Unlike the adaptive system, the pre-timed traffic control system will often operate with well-defined change points to accommodate traffic. System detection is used mostly for incident management, but the system isn't as reliant on the information collected as an adaptive system. The pre-timed system may require less funding to maintain, but this system tends to be less responsive to changing road conditions. A way to work around this is to have someone at the traffic management center to monitor traffic operations and to make changes manually. In many agencies, this is the preferred way, keeping human contact in the process.

Safety and mobility in the urban environment are not an impossible endeavor. I would recommend the following:

* Identify all stakeholders and involve them in the entire process;

* Establish priorities, knowing that they will change as time goes by;

* Keep staff up to date on new technologies and techniques;

* Research the technologies, go out and find where it is working and where it isn't;

* Benchmark against other agencies to establish effective standard operating procedures, and be aware that they do not have to be in the traffic business to be useful; and

* Be patient.

This is a brief overview of options for urban traffic control. Other issues to consider are the communication system, pedestrian safety and mobility, emergency pre-emption for fire and rescue, transit priority, incident management, detection system technology, emergency management and in the case of most cities, homeland security. There also is the political side of the traffic control system to contend with. Public policy issues can make or break a successful system. Changing priorities are difficult to program into the software.

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