Origins at the area where acidic rock was exposed on
Bald Eagle Mountain Corridor O of the
Appalachian Development Highway System was assigned in 1965, running from
Cumberland, Maryland (
Corridor E, now
I-68) to Bellefonte (
I-80) along
US 220. The portion in
Pennsylvania, from
Bedford north to
Bald Eagle, was upgraded to a
freeway in stages from the 1960s to the 1990s. The first section, from
US 30 in Bedford to
PA 56 near
Cessna, opened in the latter half of the 1960s. Two more sections—from PA 56 north to modern exit 15 in
Blair County and from
Charlottsville (exit 45) to Bald Eagle—were completed in the 1970s. The portion between exit 15 and
Altoona (exit 33) was finished in the 1980s while the segment between modern exits 33 and 45 was opened by 1997. In 1991, the
Intermodal Surface Transportation Efficiency Act (ISTEA) was signed into law. It included a number of High Priority Corridors, one of which—Corridor 9—ran along US 220 from Bedford to
Williamsport, and then north on
US 15 to
Corning, New York. The
National Highway System Designation Act of 1995 amended ISTEA; among these amendments were that "the portion of the route referred to in subsection (c)(9) [Corridor 9] is designated as Interstate Route I-99." This was the first interstate highway number to be written into law rather than to be assigned by
AASHTO. The number was specified by Representative
Bud Shuster, who said that the standard spur numbering was not "catchy"; instead, I-99 was named after a street car, No. 99, that took people from Shuster's hometown of
Glassport to
McKeesport. I-99 breaks the AASHTO numbering pattern associated with interstate highways, since it lies east of
I-79 but west of
I-81 (the number suggests it would be located very close to the
Atlantic Ocean, east of
I-95).
Designation and Bald Eagle Mountain On November 6, 1998, AASHTO formally approved the I-99 designation, which initially extended from the
Pennsylvania Turnpike in Bedford to
PA 350 in Bald Eagle. In 2002, plans were set in motion to extend I-99 northeast from Bald Eagle to
State College via
Port Matilda. The extension was fraught with issues, however. The proposed alignment for the highway north to Port Matilda proved to be controversial: while environmentalists called for I-99 to be constructed in the valley below
Bald Eagle Mountain, the
Pennsylvania Department of Transportation (PennDOT) and valley residents favored a routing that took the freeway above the valley and along the side of the ridge. Farther north, the widening of
Skytop, the mountain cut that
US 322 uses to traverse Bald Eagle Mountain, resulted in the exposure of acidic
pyrite rock in 2003. while the remaining section between Port Matilda and the west end of the
Mount Nittany Expressway near State College was completely opened on November 17, 2008. This extension, however, did not include an interchange with I-80, resulting in I-99 terminating at an at-grade intersection with Musser Lane just before reaching I-80. Further north, one short segment of two-lane highway remained between Lawrenceville, Pennsylvania, and Presho, New York, almost entirely within New York. In the early 2010s, of new freeway was constructed to connect the existing freeway segments. This provided through traffic with a continuous freeway from Williamsport, Pennsylvania, to Corning, New York, and removed traffic from the overburdened two-lane section of US 15, which was retired to county route status as
CR 115. On June 27, 2014, New York Governor
Andrew Cuomo announced that the interstate-grade US 15 freeway from the Pennsylvania border to I-86 in Corning was officially signed as I-99. ==Future==