MONTOURSVILLE, PA — Pennsylvania officially redesignated a 62-mile stretch of U.S. 15 as Interstate 99 on Thursday, completing decades of highway upgrades intended to improve freight movement, strengthen regional connectivity and support economic development in north-central Pennsylvania.
The newly designated interstate runs from the Interstate 180 interchange in Williamsport to the Pennsylvania-New York state line in Tioga County. The route will be co-signed as both I-99 and U.S. 15 after the Federal Highway Administration determined the corridor meets federal interstate design, safety and performance standards.
PennDOT Secretary Mike Carroll joined federal, state and local officials for the designation ceremony Thursday in Montoursville.
“Today’s designation of U.S. 15 as I-99 is more than a marker on a map,” Carroll stated. “This new interstate connection will strengthen the region’s economy by improving freight movement, increasing safety, and open new doors for business growth.”
PennDOT has spent more than four decades converting the corridor into a limited-access highway. Since 1984, the department has completed 34 projects totaling approximately $480 million, including roadway realignments, shoulder improvements, pavement upgrades, access modifications and other design improvements required for interstate designation. New highway signs began being unveiled Thursday.
The redesignation also connects the corridor more directly with Interstates 80 and 86, a change state officials said is expected to improve travel efficiency for commercial carriers, residents and visitors while making the region more attractive for business investment.
The interstate designation carries new restrictions for some commercial trucking operations. Under federal interstate regulations, the maximum allowable weight for divisible loads on the corridor is reduced from 95,000 pounds to 80,000 pounds unless a federal exemption applies. Divisible overweight permits will no longer be valid on the newly designated interstate, although permits for non-divisible oversized or overweight loads will continue to be issued. Milk haulers remain exempt under federal law.
PennDOT said annual permit holders affected by the changes were notified in late 2025 and again after federal approval was granted earlier this month. The department’s permit routing system began enforcing the new restrictions Thursday.
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