There's some substantial work starting Friday evening on the Parkway North and on the Parkway East and PennDOT says they expect some backups. 

In both cases, single lane traffic starts at 9 p.m. Friday night.

Let's start with the Parkway East in Monroeville with the reconstruction of the bridges over Old William Penn Highway.

"We'll be looking to cross traffic over onto the newly completed eastbound structure and do similar work to the westbound structure to replace that superstructure," said John Myler, Senior Assistant Construction Engineer with PennDOT. 

Myler says in order to do that, the Parkway East will be taken down to a single lane in each direction.

Even though it's the weekend, expect the traffic restrictions to slow you down.

"It will be queued up just with the single lane traffic for a weekend," Myler said.

While they have until Monday morning to get it back to two lanes in each direction, Myler says the work will ideally be completed sometime on Sunday. 

On the Parkway North, the I-579 temporary traffic crossover into the HOV lane will be closed.

"Once we have that closed shortly after 9 p.m., it won't take much work," Myler said. "We'll reopen the original exit to 579, which is a right exit."

To make all the necessary changes, Myler says to expect I-279 to be a single lane headed into Downtown Pittsburgh for most of the weekend into Sunday morning.

Myler says he expects the traffic change will create backups and that single lane will even be a challenge.

"We'll be moving that lane around over the weekend to accommodate the work that we need to do to restore the pavement markings," Myler said. "I would expect that to be a single lane all weekend while we're performing that work."

Like the Parkway East, Myler says the hope is to have the Parkway North and I-579 across the Veterans Bridge back to its original state by Monday morning.

In both cases, the changes are only a transition, not the end of the work.

On the Parkway East, crews have to rebuild the westbound bridge, which should wrap up by early December. 

The Parkway North work should be completed by around the same time.