VWH Campbell Jr./Post-Gazette
The eastbound lane of the Parkway East.
Closing some on-ramps and installing traffic signals on others may be the key to easing congestion and reducing crashes on the Parkway East.
The Pennsylvania Department of Transportation has budgeted $5 million for design and construction of a ramp metering system similar to those that have improved traffic flow and safety in several other U.S. cities.
On a metered ramp, a red-green traffic signal allows one vehicle at a time to enter the highway. The timing of the signals can be adjusted based on traffic volumes, but they typically allow a vehicle to pass every few seconds. In nonpeak periods, they can be turned off.
"We do have intentions of ultimately down the road implementing some sort of access control to the parkway in order to improve the safety and mobility of the road," said PennDOT District 11 executive Dan Cessna.
"Any of those changes will involve public input," he said. "Obviously, it's a volatile issue."
It won't happen soon; the construction money is budgeted for 2016 in the region's current draft Transportation Improvement Program.
The parkway "has the appropriate volume and congestion levels to consider ramp management as an alternative solution to reducing congestion," said a University of Pittsburgh study commissioned by PennDOT last year. "An area-wide simulation model shows that a combination of ramp metering and ramp closure strategies would provide the most effective congestion reduction. With this congestion reduction, several local street routes will experience an increase in traffic; however, with selective traffic mitigation strategies, this congestion will be alleviated."
The study concluded that the right mixture of ramp metering and closures could reduce morning rush-hour backups at the inbound Squirrel Hill Tunnel by two miles and reduce travel times by about 51/2 minutes. Evening backups on the outbound side could be shortened by six-tenths of a mile with more than four minutes shaved off travel times.
The study also reported that in five metro areas where ramp metering is used, peak-hour collisions declined by 15 percent to 50 percent.
The study's preferred option would close the southbound Braddock Avenue and southbound Ardmore Boulevard on-ramps to the inbound parkway during the morning rush and place meters on the northbound Ardmore and westbound Greensburg Pike on-ramps. In the evening, the Bates Street on-ramp to the outbound parkway would be metered and the Beechwood Boulevard and southbound Braddock Avenue on-ramps would be closed.
Twelve intersections off the parkway would require improvements including new turn lanes or traffic signals to ease congestion, and 72 traffic signals would require upgrades or replacement.
The study acknowledged that the system would not have much of an impact during the highest peak periods. "The bottom line is the parkway is well over capacity," Mr. Cessna said. "You're never going to totally eliminate backups at the tunnel."
The proposal is generating some buzz in eastern suburbs. At a June meeting of the Turtle Creek Valley Council of Governments, a Swissvale council member, Darrell Rapp, questioned whether it would benefit commuters from Murrysville and Monroeville at the expense of communities nearer to the affected ramps.
"My first reaction was that I wondered about whether the benefits of this are going to be evenly distributed," he said in an interview. "The general reaction I got from other elected officials there was that this would be a negative."
Ramp closures and restrictions could put more traffic on already crowded secondary roads with a ripple effect pushing more traffic onto neighborhood streets, he said. "My second general concern is that if we continually make it easier to get to the far suburbs, then people will move out of the city and move out of the first-ring suburbs," he said.
The Minneapolis metro area has hundreds of ramp meters, which have been shown to reduce rush-hour crashes by 24 percent and increase travel speeds by 16 percent, the PennDOT study said.
The system was turned off for six weeks in 2000 to evaluate its impact, and travel times and crashes increased, it said.
In Detroit, ramp metering led to a 50 percent reduction in collisions and a 71 percent decline in crash injuries.
Ramp management "has gained acceptance in many states and urban areas in the country," the report said. "The [Federal Highway Administration] and individual state DOTs have developed systems that show major benefit to the urban freeway systems. ... Many of the congestion and safety problems exhibited by urban freeways, which can be solved by ramp management, are found in the urban freeway systems of Pennsylvania. These characteristics include insufficient ramp acceleration lane length; close spacing of ramps and deficient mainline capacity during peak periods."
Two segments of the Parkway East were listed among America's most congested highways in a May report by the international traffic monitoring company INRIX. The inbound side from Business Route 22 to the Squirrel Hill Tunnels was rated 20th-worst for its morning backups; the outbound side from Downtown to Business Route 22 was 37th-worst for its evening jams.
Although the inbound Parkway West ranked higher for traffic congestion in the report, there are no current plans for ramp metering there, Mr. Cessna said. However, a PennDOT consultant is studying possible changes or improvements at the Banksville Road, Green Tree and Carnegie interchanges.
First published on August 14, 2012 at 12:00 am