Second of two parts: How ADOT and MAG plan to cut congestion and how you can help
Valley commuters’ pain is being felt by those who can make a difference in how long it takes to get to work.
Transportation planners for Arizona Department of Transportation (ADOT) and Maricopa Association of Governments (MAG) are developing ways to reduce traffic congestion during peak travel times – the morning and evening rush hour.
“If (freeway) traffic all flowed at the same speed, most congestion would be avoided,” said John Halikowski, ADOT director. “When one person taps brakes, it causes a chain reaction, and vehicles slow down for quite a distance. It takes a long time for that traffic to come back up to speed.”
Transportation planners often say that traffic flows like water—it looks for the route of least resistance—and in metro areas where there are few options, Ram Pendyala, professor of transportation engineering and director of University Transportation Center at Arizona State University, says that all traffic ends up on one of a few freeways. This is the cause of long times spent in congestion, he said, in metros like Atlanta, Austin, Silicon Valley and Los Angeles.
“In Phoenix, there are multiple options because of the street grid,” said Eric Anderson, MAG executive director. “The distributed employment centers also provide multiple destinations for commuters.”
With Maricopa County being the fastest-growing U.S. county, and one of the best job markets for new hires in the nation, traffic is increasing as well. ADOT and MAG are readying programs that will help reduce congestion without significant road improvements.
“We’ve got a number of ideas being pursued,” Anderson said. “One, dynamic ramp metering, is already in place on the (State Route) 51. Others are being planned, but were put on hold until after the high-priority ‘wrong way driver’ warning program was put into effect.”
Dynamic ramp metering still allows one vehicle per lane on a green metering light, but instead of the lights flashing in regular rhythm, the lights are timed to allow traffic to enter the freeway when there is capacity on the through lanes to accommodate the entering vehicle. Traffic can be held longer if the freeway were congested awaiting the right slot for one or two vehicles to merge.
Another ongoing MAG congestion-busting program is assignment of Department of Public Safety officers in the Valley’s traffic control center. DPS officers can literally watch for accidents and traffic situations and dispatch emergency responders within minutes.
“In Arizona, only a sworn officer can dispatch an ambulance or tow truck when there is an accident,” Anderson explains. “In the past, this meant someone would call 9-1-1, describe the scene and the first responding officer would handle other emergency response dispatch upon arrival. Now, with the officer in the control center, he can see the situation as it is unfolding, and instantly get the right crews, the right size tow truck, and emergency medical personnel to the location quickly.”
The DPS co-location program has been so effective, ADOT is deploying it statewide.
Changing driver habits is one inexpensive way to decrease traffic congestion, according to both Halikowski and Anderson. Traffic flows groups of vehicles called “platoons.” If a trailing platoon is moving faster than the one ahead of it, the lead cars in the trailing group will catch up to the first platoon. Lead drivers In the faster group then need to tap brakes to slow. Every following vehicle is forced to brake. The sudden slowdown – in addition to causing periodic rear-end accidents, according to traffic experts – slows traffic for miles while the platoons struggle back to speed.
Sometimes it seems traffic just clogs in the same place for no apparent reason. Anderson said one not-so-apparent reason is weaving and dodging by vehicles trying to enter and exit the freeway.
“It’s a major reason that the Broadway Curve on Interstate 10 is such a challenge. Weaving to get into position destroys traffic throughput,” said Anderson. “(ADOT and MAG) are looking at designs to rebuild the ramp structure and avoid the weaving in that area.”
The area Anderson references is the combination of a sharp curve and a tight convergence of interchanges from S.R. 143, U.S. 60, Broadway Road and I-10. All these interchanges hit the interstate in a two-mile segment known as the “Broadway Curve.” Vehicles are trying to jockey on and off the freeway in a highly compact area.
“Look at S.R. 143 and I-10. Traffic drops to a crawl to circle around the interchange to eastbound I-10,” he said. “We’re looking at ways to redesign the entire area. We’ll have new ramps, flyovers, and other features to reduce weaving. That will speed up traffic in that area.”
Used in a limited way on I-17 between Cordes Junction and Anthem on the steep mountain curves, ADOT is exploring variable speed limit systems on freeways. As traffic increases or weather changes on I-17, speeds are changed on digital speed limit signs to slow traffic on the accident-prone stretches of the interstate.
South of Phoenix, ADOT is exploring the same type of system for I-10 between Casa Grande and Chandler to vary speeds to as low as 35 mph, depending on visibility. Variable speed limits could be used in urban areas to slow traffic ahead of congestion and reduce brake usage.
“If everyone would go the same speed,” Anderson agrees with Halikowski. “We’d see a lot less congestion on the freeways.”
Changing driver habits is an inexpensive, and first-line approach to maintaining Phoenix’s best commute time and least time spent in congestion rankings among major metro areas. It would also have an immediately visible effect. The other changes are going to take time and money to deploy over the next few years.