I-17 101 traffic interchange

ADOT tests how ramp meter timing can improve SR 51 traffic

ADOT tests how ramp meter timing can improve SR 51 traffic

September 28, 2016

PHOENIX – With a goal of improving the rush-hour traffic flow, the Arizona Department of Transportation will test changes in the timing of ramp-meter signals along one Phoenix-area freeway.

Starting the week of Oct. 3, afternoon rush-hour drivers using on-ramps along northbound State Route 51 (Piestewa Freeway) are likely to notice longer red lights at ramp meters as ADOT takes a look at how the signal adjustments affect freeway traffic.

It will likely take a couple of days for the adjustments to be made at all of the northbound SR 51 ramp meters. The changes are expected to be in place for at least three weeks as part of this initial phase of tests.

As part of the testing, some northbound State Route 51 ramp meters may turn off at an earlier time during the afternoon rush hour based on how well freeway traffic is flowing.

The ramp meter project supports one of ADOT’s key performance indicators under Governor Doug Ducey’s call for continuous improvement among state agencies: decreasing the percentage of time freeways in the Phoenix metro area are congested.

Ramp meters have been used for years at many Phoenix-area on-ramps to enhance traffic flow as well as safety by creating gaps between vehicles entering freeways.

The testing along State Route 51 provides a way to look at the full capabilities of current ramp-meter technology. Adjusted ramp meters will respond to freeway traffic flow as well as the volume of traffic entering the freeway.

Ramp meters are currently programmed with predetermined red-light intervals. Hours of operation are based on historical traffic data.

As part of ADOT’s project, the red lights at the northbound State Route 51 ramp meters may hold vehicles for several more seconds, but detectors along the entrance ramps also will assess if ramp traffic is backing up. The system also is designed to adjust the red and green light timing to limit the amount of traffic waiting to enter the northbound freeway.

Heaviest rush-hour traffic conditions along northbound State Route 51 occur during weekday afternoons. ADOT’s project team has already been gathering data over the last several weeks for current ramp-meter and freeway conditions along the northbound freeway.

The ramp-meter timing changes may be kept in place beyond the three-week test period, based on results.

ADOT also will study another system of ramp-meter programming along southbound SR 51 in the near future, although the dates for that research haven’t been set. That additional programming system is designed to allow individual ramp meters to respond to traffic conditions even several miles away and adjust signal timing to help improve traffic flow along a longer stretch of freeway.

ADOT is working closely with the city of Phoenix on the ramp meter research project and will monitor any impacts to traffic on local streets intersecting with SR 51.