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PennDOT plans new interchange designs on I-70 in Washington Co.

| Monday, April 14, 2014, 1:01 a.m.

With new money from the new state highway law, the Pennsylvania Department of Transportation will undertake major improvements to interstate highway interchanges.

And it will utilize two innovative engineering designs to improve safety and traffic flow.

During an outreach meeting last week, PennDOT officials detailed the designs – roundabouts and divergent diamond interchanges – planned for some Interstate 70 projects over the next two years in Washington County.

Much of the work is being funded through Act 89, the state transportation law.

The statute, signed in November by Gov. Tom Corbett, removed the 12-cents-per-gallon retail gas tax but uncapped the Oil Company Franchise Tax.

The roundabout interchange is now the state's favored interchange – when feasible.

“We start with a roundabout for every project,” said Rachel Duda, PennDOT District 12 assistant district executive.

“When we dismiss it, then we look at four-way intersections.”

That was the case with a project slated for the intersection of routes 88 and 837 in the Fisher Heights section of Carroll Township. A roundabout was initially planned, however, the land needed for the project would have cut deeply into the Giant Eagle parking lot. PennDOT scrapped the design idea.

A roundabout, though, is planned for improvements to the I-70 Bentleyville interchange.

The proposed project involves safety improvements to the I-70 corridor, encompassing interchanges 32A and 32B.

It would provide a wider median, lengthen and reconfigure ramp acceleration and deceleration lanes, replacement of the bridge carrying I-70 over Pigeon Creek and Norfolk Southern Railroad, replacement of the bridge carrying Route 917 over I-70, and the potential elimination of the Route 917 (Pittsburgh Road) interchange.

The project is slated to be bid in 2015. Construction would begin in 2016.

PennDOT plans to construct a roundabout interchange at Exit 32B (Bentleyville exit).

Roundabouts are most commonly used at the ends of ramps, Duda said.

Duda said the roundabouts are more efficient at keeping vehicles moving. When accidents occur, vehicles do not collide at angles.

“It's usually rear end and, thus, less severe,” Duda said.

In roundabouts, drivers don't stop at stop signs. Rather, roundabouts create yield conditions.

Roundabout system use is limited, because slope can affect design and construction.

“Our terrain here is hilly,” Duda said.

At the intersection of state Route 519 and Brownlee Road in North Strabane Township, a dual roundabout will be utilized. It will resemble a figure eight, except the two roundabouts will not touch.

“It will be done because the traffic signals would not give us the capacity for left-hand turns,” Duda said.

The project aims to improve a dangerous intersection that has been the site of several serious accidents, including one fatal crash in 1997.

The divergent diamond – or double crossover diamond interchange – is new to PennDOT.

This formation will be used for the first time on a Pennsylvania highway at the I-70 Murtland Avenue Interchange in South Strabane Township, said Bill Beaumarriage, District 12 portfolio manager. In the divergent diamond, the one lane or set of lanes of traffic travel above the perpendicular lanes of traffic.

When the Murtland Avenue project is completed, those driving north on Route 19 will cross over and drive in the left-hand lanes, Beaumarriage said.

“But the design is so that you don't realize it,” Beaumarriage said. “It makes it easier to make lefts.”

The $57 million project will be advertised for bid in July and work might begin this fall. It will improve on- and off-ramps and add a third lane heading to I-79.

“This project will set us up for future projects on I-70,” Beaumarriage said.

Chris Buckley is a staff writer for Trib Total Media. He can be reached at 724-684-2642 or cbuckley@tribweb.com.

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