Mercer County is now the home of three interstate highways as Route 60 was declared Interstate 376 on Friday.

This 85-mile interstate runs from the I-80 interchange in Shenango Township to the Pennsylvania Turnpike in Monroeville.

Signs will steadily be erected over the coming year to show the corridor is now a full-fledge interstate.

Earlier this year the I-279 section of the corridor between Interstate 79 and the Fort Pitt Tunnel was converted to I-376.

The roadway previously was designated as three different routes including I-279, U.S. Route 22/30 and Route 60. The 16.5 mile-stretch of Toll 60 will remain a toll road and still be under the Pennsylvania Turnpike Commission’s control but has been designated part of I-376 corridor.

Route 60 is now solely in Allegheny County between the West End in Pittsburgh and I-376 in Robinson Township.

The announcement was made in Pittsburgh by Allen Biehler, Pennsylvania Department of Transportation Secretary along with federal, state and area officials.

Having three interstates: I-80, I-79 and now I-376, boosts Mercer County’s economic growth prospects, said Larry Reichard, executive director of Penn-Northwest, the county’s lead development agency.

“I think this is great news,’’ Reichard said. “It certainly looks prominent on a map. We now have an interstate connecting us to the Pittsburgh Airport and the city of Pittsburgh.’’

The designation by the Federal Highway Administration caught many local officials by surprise as much work to transform the highway to meet interstate regulations still remains. Part of that work includes creating a full diamond interchange near I-80 in Shenango Township. Currently only a half diamond exists but construction plans are in the works to build a full diamond at the site.

“There are still a number of large projects to be completed,’’ said Dan Gracenin, Mercer County Regional Planning Commission director. “But the highway administration can make a designation if it’s shown these projects will be completed in the near future.

More than $20 million in American Recovery and Reinvestment Act funds are being used to make the improvements required for I-376’s designation. Specifically, more than $13.7 million in Recovery Act funds are now being used to improve the 20/30/60 interchange in Robinson Township. Additionally, nearly $9 million in Recovery Act funds will be used to make improvements to Route 60 in Lawrence County, said U.S. Rep Jason Altmire, D-4th District, McCandless.

“The designation of I-376 has been a top priority for myself and other local leaders for years, because we all know that this federal interstate will help us attract new businesses and new jobs to western Pennsylvania,” Altmire said. “The designation of I-376 is literally putting our region on the map as a place that has the highway infrastructure that businesses are looking for when they consider where to expand and relocate.”