PUBLIC WORKS/Agencies upgrade system for traffic management

All systems were “go” when, earlier this year, a consortium of local, state and regional agencies completed the $14 million upgrade of the Las Vegas Area Computer Traffic System (LVACTS). The computerized system, which controls traffic signal timing along major roadways, is effectively reducing travel time, fuel consumption and pollution in Las Vegas, North Las Vegas, Henderson and Clark County.

The original LVACTS was built in 1984. Accommodating up to 500 signals, it used centralized architecture, which required communicating with field devices at least once a second to gather vehicle volume, occupancy and speed data. That information was then used to time all signals from a single traffic-control center.

Soon after the initial system went live, a study of six arterials in the Las Vegas area showed reductions in travel time (down 17 percent), fuel consumption (23 percent), delays (38 percent), carbon monoxide emissions (24 percent) and stop times (48 percent). Although the system produced tangible benefits, it could not keep up with growth in the Las Vegas area, and, by 1998, it reached its 500-signal capacity.

Anticipating the need to expand the system, the LVACTS Operating Management Committee (OMC) began planning an upgrade in 1992. (Las Vegas acts as the Central Operator for LVACTS, but the OMC — consisting of representatives from Las Vegas, North Las Vegas, Henderson, Clark County, the Regional Transportation Commission and the Nevada Department of Transportation — determines operating policy and stakeholder duties. Policy is established with each agency having one vote.)

In addition to expanding system capacity, the OMC wanted to improve reliability and flexibility, says Niel Rohleder, LVACTS manager. “[With the old system,] we had instances when the mainframe computer crashed, and we were not able to run a coordinated system of traffic signals,” Rohleder explains. “In 1996, we lost it for about three-and-a-half days, and the commute times went from what was normally about 20 minutes to an hour.”

To alleviate that problem, the OMC worked with contractor Barton Aschman (now Pasadena, Calif.-based Parsons Transportation Group) to design an upgrade based on distributed rather than centralized technology. The committee broke ground on the project in 1994, installing advanced traffic control (ATC) devices at 620 intersections and installing communication servers, or hubs, at 11 sites throughout the region.

“The ATCs communicate with traditional 22-gauge telephone wiring from the intersections to the hubs,” Rohleder says. “A standard 10/100 Ethernet connects IBM-based computers, tying the hubs to [the LVACTS traffic management center]. The Ethernet uses licensed microwave technology and fiber optic facilities that are owned and controlled by LVACTS.”

The last of the traffic signals controlled by LVACTS was converted to the new system in June 2002. With the distributed architecture, the system intelligence has shifted from a central point to the intersections and the hubs. As a result, system-wide failure is “virtually impossible,” Rohleder says.

“We will still rely on a single traffic-control center, but, if it were disabled for some reason, [the system] would not necessarily need to be operated at that location,” he notes. “If we lose communication from central, the ATCs will remain coordinated with those around them.”

In addition to being more reliable than the old system, the new LVACTS gives the traffic management staff more computer power to solve difficult traffic situations. “If traffic lights need to be adjusted to accommodate school hour changes, extended store hours for holiday shoppers or traffic backups due to an accident, we now have the tools to make those adjustments,” Rohleder says.

Currently, LVACTS is used to control traffic across 306 miles of roadway, and Rohleder estimates that, over the next three years, the OMC will expand the system to cover an additional 100 miles per year. (The new LVACTS can accommodate up to 9,999 traffic signals.) In the meantime, the LVACTS staff is evaluating the new network and revisiting specific locations to fine-tune timing for maximum traffic flow.

The Nevada Department of Transportation administered the LVACTS upgrade, which was funded primarily through the Intermodal Surface Transportation Efficiency Act. Ongoing operations and maintenance costs are paid by those OMC agencies that maintain traffic signals; each agency pays in proportion to the number of signals it has in its system.