Despite another close call from yet another major rockfall, the Pennsylvania Department of Transportation is keeping Route 28 open through Harmar.

Drivers are being funneled into one lane in each direction "until further notice," as PennDOT phrased it, while cleanup takes place and work continues on long-term safety measures in the slide-prone area between Exits 10 and 11.

The temporary traffic pattern was established on the northbound side around 3:30 p.m. yesterday, about 12 hours after boulders broke loose and tumbled onto the road, leading to an overturned tractor-trailer and causing a chain-reaction car accident.

Had the rockfall occurred several hours later, the outcome could have been tragic. During morning rush hours, a steady stream of single-lane traffic files through the area where one lane already was closed for construction and the hillside stabilization project.

PennDOT engineers plan to maintain the temporary traffic pattern near RIDC Park for at least a few days while they assess the stability of the hillside, where a contractor has been working to minimize and control landslides.

Engineers also are considering keeping Route 28 as a single lane each way for several more weeks, until construction of a new southbound lane will be completed in the grass median and drivers can be shifted a lane-width away from the abutting hillside. The existing southbound right lane will become part of a wider shoulder and drop zone to snare future rock falls.

PennDOT spokesman Jim Struzzi said traffic will not be restored on the southbound side of the highway until geotechnical engineers are certain of its safety.

Yesterday's incident caused major congestion, because Route 28 was initially closed and later limited to one lane northbound, and because one of the rig's two tandem trailers toppled over the edge of a hillside above Freeport Road, restricting traffic there.

At least three cars were involved in a crash on the southbound side when drivers slammed on their brakes to avoid the fallen rocks.

People seeking ways around the incident overwhelmed streets through Aspinwall, O'Hara, Fox Chapel and Oakmont. The backlog extended to the Pennsylvania Turnpike, where drivers unable to exit at the toll plaza backed up onto the east-west mainline.

The Port Authority reported that buses that use Route 28 operated up to an hour behind schedule.

PennDOT is spending $5.1 million to shift the highway and stabilize a half-mile of the hillside where slides have been most frequent. The contract includes installation of a 15-foot-high, 1,600-foot-long steel mesh fence to prevent falling rocks from tumbling onto the highway.

PennDOT District 11 Executive Dan Cessna has previously said the changes are not a cure-all. "While the public needs to understand this will not eliminate rock slides, these efforts should lessen the impact of future rock falls and dramatically improve public safety," he said last month.

While there have been numerous close calls, nobody has been seriously injured in the slides that have plagued the four-lane, divided section of Route 28, also known as the Allegheny Valley Expressway.

Yesterday, the driver whose rig overturned in the northbound lanes was treated for minor injuries at a local hospital and released.

State police Lt. Tom Dubovi, of the Kittanning barracks, said the driver tried to swerve out of the way of falling debris but was unable to avoid a concrete jersey barrier that was pushed into the middle of the highway by hundreds of tons of rock.

The rocks that broke loose were as big as cars and weighed as much as 40 tons. The rock fall occurred close to where crews have been rappelling over the side of the hill to break off loose rocks. As a result, many of the rocks -- including the largest ones -- landed in a small basin that had been excavated to catch the climbers' debris, Mr. Struzzi said.

PennDOT added the hillside work to a contract to improve 6.8 miles of Route 28 in Harmar, O'Hara, Springdale, Frazer and East Deer this year and next, including adding a 1.5-mile-long northbound lane to the Pittsburgh Mills shopping center.

Route 28 ramp to close

The southbound Route 28 on-ramp at the Route 910 Harmar interchange will be closed to traffic this weekend, from 10 a.m. Friday through 5 a.m. Monday, for concrete patching work.

The ramp in Harmar will be closed as part of a $35.8 million improvement project on Route 28 in O'Hara, Harmar, Springdale, Frazer and East Deer.

A suggested detour is northbound Route 28 to Springdale/Cheswick, Exit 12. Then exit and re-enter southbound Route 28.