Officials with the Utah Department of Transportation say the goal is to maintain the road's efficiency while simultaneously increasing safety, especially for the road's heavy truck traffic.

April 08, 2009

LINDON, UT—SmartSensor Advance is providing dilemma zone protection at several intersections along one of Utah's deadliest stretches of road. However, what's interesting about this project is that the intersections are part of a coordinated signal corridor. Officials with the Utah Department of Transportation say the goal is to maintain the road's efficiency while simultaneously increasing safety, especially for the road's heavy truck traffic.

State Road Six is a four-lane arterial with posted speeds of 60 mph. A limited access highway, SR-6 runs east/west through Spanish Fork Canyon and has an average annual daily traffic count of 14,117; 19 percent of that is heavy trucks. Mark Taylor, a signal systems engineer at UDOT, says because of the corridor's unique characteristics, it was decided that signal coordination would provide better progression and fewer stops along the highway.

"The concern is for the large number of trucks traveling this road," Taylor says. "For example, the westbound trucks travel many miles down the steep canyon and typically ride their brakes. Synchronizing the signals to favor westbound traffic reduces the stops for these trucks."

It is common practice in the traffic control sector not to combine dilemma zone protection and coordination because the fixed time of coordinated signals typically overrides any detectors providing dilemma zone protection. "Some argue that the dilemma zone is reduced anyway with coordination," Taylor explains. "If signals are properly synched, then vehicles don't have to stop, so essentially there is no dilemma zone."

However, UDOT liked the additional benefits of dilemma zone protection and saw it as a way to increase safety. "The first SmartSensor Advance on SR-6 was installed three years ago as part of an advance warning system, and since then, we've added four additional sensors," Taylor says.

To make the system work, UDOT chose to pair SmartSensor Advance with Econolite ASC/2 and ASC/3 traffic controllers, which feature an advanced, "actuated-coordinated" function. Taylor says, "Essentially what this does is allow the traffic signals to run in coordination, with a window at the yield point of the coordinated phases where the traffic signal detectors on the main line become actuated." This method provides UDOT with two benefits: first, it reduces stops for large trucks and other vehicles trapped in the dilemma zone; and second, it offers extra protection by allowing SmartSensor Advance to look for a safe gap in approaching traffic before terminating the phase.

Currently, UDOT is performing travel time studies to determine if the system has been successful.