I-99 designation becomes official for U.S. 15 corridor
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A 62-mile stretch of U.S. 15 between Williamsport and the New York state line officially became Interstate 99 on Thursday, marking the completion of a decades-long effort to upgrade the highway into a limited-access interstate corridor, according to a news release from the state.
Pennsylvania Department of Transportation Secretary Mike Carroll joined federal, state and local officials to celebrate the designation, which follows approval from the Federal Highway Administration that the roadway meets interstate standards for design, safety and performance. The highway will be co-signed as both Interstate 99 and U.S. 15.
State transportation officials said the interstate designation is expected to strengthen freight movement, improve regional connectivity and help attract new business investment to north-central Pennsylvania.
"Today's designation of U.S. 15 as I-99 is more than a marker on a map," Carroll said. "It reflects the investment, collaboration and engineering excellence of countless individuals who understood how vital this route is to the future of the region."
Carroll said the new interstate connection will improve freight transportation, enhance safety and create opportunities for economic growth by better connecting the region to major transportation networks.
PennDOT has spent more than four decades transforming U.S. 15 into a continuous limited-access highway. Since 1984, the department has completed 34 projects totaling approximately $480 million, including new roadway alignments, shoulder improvements, pavement upgrades, intersection and access modifications, and geometric improvements.
New interstate signs have been installed along the corridor and began being uncovered Thursday.
PennDOT District 3 Executive Eric High called the designation a milestone for the region.
"The completion of I-99 marks a transformative milestone for our region," High said. "One built through decades of investment, persistence and partnership. This designation strengthens connections for businesses, travelers and communities and reflects our commitment to infrastructure that supports long-term growth."
The newly designated interstate extends from the Interstate 180 interchange in Williamsport to the Pennsylvania-New York border in Tioga County, where it connects with Interstate 86. The corridor also provides access to Interstate 80, creating a more direct interstate connection through north-central Pennsylvania.
The designation also brings changes for commercial trucking operations.
Because the roadway is now part of the federal interstate system, the maximum allowable weight for divisible loads is reduced from 95,000 pounds to 80,000 pounds, unless a federal exemption applies. PennDOT said annual permits for divisible overweight loads will no longer be valid on the I-99 corridor, although federally exempt milk haulers may continue operating overweight on the route. Haulers exceeding the new weight limit must use alternate state routes authorized under existing permits.
Permits for non-divisible oversize and overweight loads will continue to be issued for travel on Interstate 99. PennDOT said affected permit holders were notified of the upcoming changes in late 2025 and again after federal approval was granted earlier this month.