PHOENIX – Starting this week, the timing of ramp-meter signals along southbound State Route 51 (Piestewa Freeway) are being adjusted to respond to the flow of morning rush-hour traffic, expanding an Arizona Department of Transportation program that began last fall along the freeway’s northbound on-ramps.
Instead of the ramp meters being programmed with predetermined red-light intervals, the system will use data from traffic-flow sensors embedded in the freeway’s pavement to adjust the signal timing. When morning rush-hour traffic slows, the ramp meters may hold vehicles several additional seconds to help ease the congestion.
The change involves southbound SR 51 on-ramp meters from Greenway to Thomas roads. The southbound ramp meter at Shea Boulevard isn’t currently in use.
As with the northbound State Route 51 ramp meters during the afternoon rush hour, the southbound meters may even turn off earlier in the morning based on how well freeway traffic is flowing.
Drivers may notice new signs along southbound SR 51 on-ramps advising them of the signal timing changes.
The ramp meter project supports one of ADOT’s key performance indicators under the Arizona Management System championed by Governor Doug Ducey: reducing the percentage of time freeways in the Phoenix metro area are congested.
Ramp meters have been in use for many years across the country and at many Phoenix-area freeway on-ramps during busy rush hours to enhance traffic flow, as well as safety, by controlling the number of vehicles entering freeways at any one time.
The upgrades along SR 51 provide a way to look at expanded capabilities of ramp-meter technology. Most ramp meters along Valley freeways are currently programmed with predetermined red-light intervals. Hours of operation for the meters have been based on historical traffic data.
The SR 51 ramp meters using the new responsive system are programmed to adjust to freeway traffic flow and the volume of traffic entering the freeway. Detectors along the entrance ramps also assess if ramp traffic is backing up, allowing the system to further adjust the red and green light timing to limit the amount of traffic waiting to enter the freeway.
ADOT is working closely with the city of Phoenix on the ramp meter research project and will continue to monitor any impacts to traffic on local streets intersecting with SR 51.