PROSPECT – The Maine Department of Transportation has closed the southbound shoulder on Route 1 near the blasting area for the approach to the new Penobscot River bridge and on Monday began installing concrete safety barriers.

The move is in response to an incident early in February in which a large piece of the ledge fell onto the roadway. A motorist struck the rock before construction workers could remove it.

Crews have been blasting in the area since October to remove an estimated 150,000 cubic yards of rock to create a new Route 1 approach to the bridge that will replace the Waldo-Hancock Bridge.

Although had been no blasting in that immediate area when the rock fell, DOT officials speculated that earlier blasting may have loosened the rock and that warm weather had caused it to break off the ledge.

According to DOT spokeswoman Carol Morris, department officials have been examining the rock since the incident to determine the level of risk and the best safety solution. Because of the naturally fractured nature of the rock face, moving the traveling public farther away from the site has been determined to be the best and safest solution.

The DOT had closed the shoulder with traffic control cones. The concrete “Jersey” barriers were delivered from DOT storage on Friday and crews began installing them Monday morning. The closure zone begins just south of the Route 1 and Route 174 intersection and extends for 750 feet.

The department will shift traffic slightly away from the barriers, which will be placed at the white line marking the edge of the travel lane.

“They’ll shift traffic out a little bit,” Morris said Monday. “The speed limit is 35 there, so it won’t change the speed limit.”

Cones or barrels will be used to direct traffic through the new travel lanes, she said.

Once the concrete barriers are in place, DOT crews will construct a 12-foot-high rock berm in the shoulder and the ditch behind it. The berm will slope away from the roadway and is designed to prevent loose rocks from falling into the roadway. It also will add an extra level of protection to passing motorists as the blasting moves gradually closer to the road several months from now.

The berm will be constructed with a flat top in order to be accessible to an excavator that will remove any material that falls from the exposed rock face.

Recent blasting has been limited to small “pre-split” blasts to produce a smooth rock face, Morris said. Crews are now ready to begin using larger production blasts to move the bigger rock pieces down to the final roadway elevation.

“People are going to see and hear bigger blasts as they take out very large quantities of rock,” Morris said.

Approximately 70,000 cubic yards of rock has been blasted from the site so far. When the blasting is complete at the end of this summer, a total of 150,000 cubic yards of rock will have been removed.

The barriers will remain in place until the blasting is done.