The environmental overview will address air quality, wetlands, regional growth, noise and traffic.
Punt announced last May that PennDOT committed to widening the heavily traveled highway, in keeping with plans in Maryland, West Virginia and Virginia to expand parts of I-81 in those states.
The project will encompass 77 miles of highway from the Maryland/Pennsylvania boarder to Pa. 581south of Harrisburg, where it already is six lanes, and from the Interstate 83 interchange in Dauphin County to the Interstate 78 interchange in Lebanon County.
The key arguments for widening the highway are traffic volume and safety.
With anywhere from 40,000 to 80,000 vehicles traveling on I-81 in Pennsylvania daily, the interstate is the second-most traveled north-south highway in the East. Only Interstate 95 is busier.
Punt said motorists won't notice any physical activity during the study other than some traffic counters.
"We're really gathering and assembling information we need to move into the next phase, which is engineering and design," he said.
It will be several years before Franklin County residents see any construction.
"The best-case scenario is five years," Punt said.
Construction could take eight or nine years depending on what the study determines, Punt said.
The cost of the project is estimated at $400 million to $600 million, paid for with state and federal funds.
Punt said the actual price tag won't be available until after the engineering and design work.
PennDOT Spokesman Greg Penny said the current contract is significant because the agency wasn't even considering widening the highway until last year.
"Our focus was to preserve or fix existing roadways," Penny said. "Sen. Punt really pushed to get the feasibility study under way and to get a handle on how much it will cost."
A Web site updating the study will be established within the next couple of months to keep the public informed on the progress, Penny said.
Public meetings likely won't begin until the fall because of the amount of information to be collected and analyzed, Punt said.
PennDOT selected DMJM & Harris, a Philadelphia engineering company, to perform the study. Other firms will assist with the traffic analysis and environmental overview.