Aug 14, 2003

What are the city's limits?

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

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

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

* 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.

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.