Three closures of Interstate 79 this week left drivers and police frustrated while road crews tried to solve the problem without getting stuck themselves.

State road workers reported salt was not de-icing the road, so state police shut down the interstate while road-grading equipment chipped away at the ice.

Mark Hillwig, state Department of Transportation District 10 spokesman, said the temperatures were too cold for salt to work.

"We have heavier crews on the interstate, but once the ice bonds to the road, there isn't much we can do," he said.

With the ice unable to be scraped off while traffic continued, state police rerouted vehicles to Route 19.

A stretch of Interstate 79 from the Cranberry Township to Zelienople exits northbound was closed for about an hour Thursday morning.

The southbound lane was closed Wednesday until 7 a.m. because of ice-related accidents, and the northbound lane was closed later in the day from Cranberry to Portersville.

State police made the decision to close I-79 based on reports of accidents, said Cpl. Kenneth Minyon with the state police barracks in Butler.

PennDOT officials said this section of I-79 was most affected because of icy and windy conditions mixed with high traffic volumes and inexperienced motorists.

Police generally ask fire and municipal police departments to help close an interstate. They shut down on-ramps first, then reroute traffic off at the detour exit with as many emergency vehicles that are available, state police said.

Traffic was rerouted to Route 19, backing up traffic in Jackson Township.

"With traffic backed up, you have trucks sitting on these patches of ice. They can't move, then that backs up traffic even more," said Jackson Township Police Chief Len Keller.

He said there were no major accidents, but his officers had to focus their energy on keeping traffic under control.

"You can see why 79 was built, because Routes 68 and 19 cannot handle that kind of traffic," he said.

But in Zelienople, traffic did not present a large problem, said Jim Miller, Zelienople police chief.

"It actually seemed like less traffic on Thursday. Maybe more people were staying home," said Miller. "Everything went pretty smoothly."

Shawn Houck, another Penn-DOT spokesman, said the same problem was common throughout the region. But in other places there was less traffic, less wind or motorists knew the road better, he said.

He said a lot of drivers traveling from the southern part of the U.S. use I-79 near Cranberry where it intersects with the Pennsylvania Turnpike. These drivers may not be used to the harsh, cold weather, he said.

"It just takes one vehicle ill-equipped for the cold to spin out, and there's nowhere to go. The (road's shoulders) are not cleared yet, and even the passing lane was not cleared. So there's no way to get around," said Houck.

Concerning the road itself, Houck said trucks clear the roads and then spread salt. The second time they attack roads, plows are raised slightly so the salt is not cleared away, leaving a bit of snow.

"The problem started with the low temperatures," he said.

The cold weather kept the snow from melting, even with salt. Then traffic packed down the existing snow and it re-froze.

PennDOT workers did not add more salt, since it was ineffective. Hillwig said they could also spread small stones to add traction, but the ice was still there.

With people sliding on the roads and the danger of trucks losing control, state police closed the road.

"Our policy is that we close the road until the problem is corrected," said Minyon. In this case, transportation workers brought out road graders.

"We're putting in our full efforts here. Hopefully (with) the sun coming out, the salt will start to work," Houck said.