The Pennsylvania Department of Transportation plans to invest nearly $60 million over the next three years to improve the Parkway West between Interstate 79 and the Fort Pitt Tunnels.
Still-evolving plans include milling and repaving the entire five-mile section, bridge and shoulder rehabilitation and replacement of the crumbling concrete median barrier, said Dan Cessna, PennDOT District 11 executive.
Most construction would occur in 2014 and 2015. While modest safety improvements will be made at deficient interchanges, drivers shouldn't expect faster travel after the orange barrels are gone from what is one of the nation's most congested corridors, he said.
Physical and financial constraints rule out significant expansion of capacity on the parkway mainline, he said. Major reconfiguration of the substandard Carnegie, Green Tree and Banksville interchanges will come later, if funding is available.
"The bottom line is the Parkway West has a ton of asset management needs. The walls supporting the shoulders are in bad shape. The median barrier is crumbling. The pavement is 8 years old," Mr. Cessna said.
Some "critical" repairs were made to bridges near Carnegie in recent years and the coming construction project "will continue that investment," he said.
According to a report by consultant Michael Baker Jr. Inc., 100,000 vehicles use the parkway between I-79 and the tunnels on a typical weekday, with volumes of 7,000 to 9,000 per hour at peak times. The worst congestion is inbound during the morning rush, when it takes an average of 26 minutes to reach the tunnels, according to the report.
A report by the traffic monitoring company INRIX this year rated the section from Green Tree to the Fort Pitt Tunnels during the morning rush as the most congested in America outside of New York and Los Angeles.
The highway also has a higher-than-normal incidence of crashes, according to the Baker report, which said "this is expected since the Parkway West is a congested older corridor with narrow shoulders and rolling terrain."
Five years of data showed the four most crash-prone segments of the parkway were on the inbound side. The section between the Poplar Street and Greentree Road on-ramps had the most crashes, 114.
The others were between the Rosslyn Farms on-ramp and the bridge over the West Busway (100); between the runaway truck ramp and the Fort Pitt Tunnels (97); and the area approaching the Poplar Street on-ramp (75).
The most crash-prone outbound segment was from just before the Greentree Road on-ramp to the Poplar Street on-ramp, with 72 crashes.
Design is about to begin for the first phase of construction, which in addition to resurfacing and bridge rehabilitation, will have several "low-cost operational and safety improvements within existing rights-of-way on existing shoulders ... like extending ramp acceleration and deceleration lanes," Mr. Cessna said.
A bridge at Carnegie where the outbound on-ramp was reconfigured five years ago, adding a third travel lane, will be renovated to widen the shoulders by four to six feet in both directions.
The median barrier replacement will include taller concrete glare screen in places where it won't hinder sight distance. The intent is to block nighttime glare from oncoming traffic.
The outbound junction with Interstate 79 will be reconfigured to provide two exit lanes and two through lanes, rather than the current three-lane pattern where traffic in the middle lane can go either way.
The outbound acceleration lane at Poplar Street will be lengthened using the existing shoulder.
The Baker report identified several deficiencies at interchanges in the corridor, some of which are quite familiar to regular users.
The inbound off-ramp at Carnegie has a short deceleration lane followed by a sharp curve. Rear-end crashes occur when drivers slow before reaching the deceleration lane.
The inbound on-ramp at Carnegie has a short acceleration lane, leading to crashes at the merge point and backups as drivers wait for gaps to enter the parkway.
The Poplar Street on-ramp to the inbound parkway has a stop sign, and drivers have only 550 feet to get up to speed and merge before reaching the Greentree Road off-ramp.
The Greentree Road ramp backs onto the mainline during peak periods. Some aggressive drivers use the long right lane approaching the exit to jump ahead of stopped traffic on the mainline. Others exit at Green Tree and use the Parkway Center on-ramp to jump line, the consultant noted.
The inbound Banksville interchange causes conflicts between drivers weaving left to enter the parkway or moving right to exit to Route 51. Traffic during peak hours backs up to Green Tree and beyond.
On the outbound side, the configuration of the Green Tree interchange creates several challenges for drivers.
The right lane of the three-lane section climbing the hill toward Green Tree functions as a truck lane, but some heavy vehicles won't use it for fear of being "trapped" and forced to exit at Green Tree. That puts slow-moving vehicles in the center lane, causing congestion and a chaotic pattern of faster vehicles passing on both sides.
The on-ramp from Greentree Road has a stop sign and leaves only 400 feet to accelerate and merge before the exit ramp. Many drivers opt, instead, to enter from Poplar Street, which has a short acceleration lane.
Mr. Cessna said major reconfiguration of the Carnegie and Green Tree interchanges would be a second phase of parkway improvements, if funding becomes available. The Banksville interchange would be the third phase.