Old Penna Pike to go

Old PA pike to go

America's oldest automobile era turnpike is on the way to the dump — the pavement anyway! The Pennsylvania Turnpike is moving to begin its first complete rebuild of the original 260km Carlisle to Pittsburgh section. On most other highways pavement laid in the 1950s and 1960s has broken up and been rebuilt but the Penna pike was exceptionally well constructed, according to research manager John Hickey.

"They built this one as well as they knew how. It's got a 9" (23cm) thick reinforced concrete slab, and we've kept it up as well as we know how. There are asphalt overlays of 6 to 8 inches (150-200mm) on top of the concrete. But the trucks rock the slabs and the overlays are cracking and eventually the slabs break up. The concrete itself is breaking down in many places."

Hickey says that for several years the Pike has been keeping the old pavement alive by sending crews out to stabilize rocking slabs before overlay work is done. They drill holes in the pavement and use high-pressure pumps to fill voids under slabs with grout. But the grout-mill-repave jobs are not lasting long enough, so the Turnpike Commission has decided it is time to rebuild from the bottom.

"We have an opportunity during a rebuild to apply some technologies they didn't have then such as a permanent porous layer that will give us better sub-pavement drainage. Now we are getting water laying under the slabs and the base can become a kind of slurry or soup. Fines get pumped in there by the moving slabs and then without solid bearing the slabs just rock as the trucks go over. You can stand and see the pavement move in places."

Asphalt vs concrete

The pike is likely to seek bidders shortly for reconstruction for the first complete rebuild — a 8km section west of Allegheny Mountain. Hickey says the Turnpike will learn from its experience on this section before moving to rebuild longer sections. The Turnpike will upgrade breakdown shoulders to mainline strength so by using shoulders, narrowing lane widths and moving median barriers it can maintain 4-lane traffic flows through worksites.

Hickey says though he personally favors concrete it is likely the first pavement rebuild will be with asphalt, in part because it is easier to lay in a trafficked worksite: "In tight spaces asphalt is easier to work with and you can get traffic on it right away." Wherever the base concrete is in reasonable condition it will be turned to rubble ('rubblized') as base for the new asphalt pavement. Hickey says he suspects the concrete people will be working to find ways of being competitive with asphalt for future sections of the rebuild.

Jersey barriers vs steel

Medians barriers be concrete — moveable 'Jersey' style barriers 12' (3.6m) long and 4' (1.2m) high. The pike dropped its fatality rate dramatically in the mid-1960s when it was one of the first highways to complete a continuous median barrier and has tried different types and heights of barriers, from simple steel W-channel through shock-absorbing filled systems, even linked barrier sections moved by a special straddle vehicle. Hickey says the different systems have their pros and cons and it is a matter of safety testing, cost and judgment which to buy.

On balance Hickey says the pike prefers the simple12' standalone concrete Jersey barrier segments that workcrews can move with a boom or a loader. 1.2m seems to be optimum height, high enough to block most headlight glare from the opposing lanes and keep errant trucks from climbing over, without being so high that drivers feel hemmed in by a concrete wall.

An even bigger issue will be when and whether to build to 6-lanes. The present mainline pike outside is 4-lanes, except in the Philadelphia metro area and through though steep sections which go from 2 to 3 lanes for a truck climbing lane. But with 70,000 vehicles per day average the highway is nearing capacity at 4-lanes.

Hickey commented at a recent conference that many car drivers on the pike don't like driving alongside heavy trucks which constitute some 30% of total vehicles and which often form long convoys. The pike once studied a dual/dual roadway format with a 2/2/2/2 section with separation of trucks and buses from light vehicles, but this couldn't be justified financially. When it comes to widening the pike the issue will be revisited.

New tunnels

Another problem is tunnel capacity with twin 24' tubes at four major mountains -- Allegheny, Tuscarora, Blue and Kittatinny. A possibility is that the pike could build third tubes for trucks. Hazardous materials cargoes are presently banned from the tunnels and another possibility is truck bypass roads through deep open cuttings. The pike has been steadily rebuilding old 13' concrete arch overbridges along the length of the mainline, replacing them with higher steel structures, including some with unusual and elegant steel stanchions. They are built to a higher clearance and most are long enough to allow the mainline to be widened from 4 to 6-lanes. The pike's original interchanges were built to tight radius curves and may need enlargement. (Contact PA Turnpike 717 939 9551)