The Pennsylvania Turnpike Commission (PTC) needed to replace the existing 1950s Hawk Falls truss bridge over Mud Run on the Pennsylvania Turnpike Northeast Extension (I-476).
The functionally obsolete truss bridge is being replaced by a new, aesthetic arch bridge that is designed to fit in with Hickory Run State Park. The bridge traverses a deep gorge popular with hikers and anglers in the Pocono Mountains just outside of Albrightsville, Pennsylvania.
“The impetus for the project was the condition of the existing bridge. It had become structurally deficient and had some corrosion issues,” said Tom Murphy, Senior Vice President, Modjeski and Masters, Inc. “There were negligible shoulders on the bridge, and really that no longer meets modern highway needs.”
Design consultants Modjeski and Masters, Inc., partnered with general contractor Trumbull Corporation and construction manager STV, Inc., for the $88 million toll-supported project. Construction kicked off in the fall of 2021, with completion anticipated for late 2026.
The original three-span deck truss bridge is 738 feet long with deck I-beam approach spans carrying two lanes of traffic in each direction. It was nearing the end of its design life because it was considered to be functionally obsolete due to a lack of roadway shoulders.
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The solution is a 720-foot-long steel structure, with a 480-foot deck arch span flanked by four 60-foot deck plate girder spans.
The new bridge has three arches, each with 11 segments. Each arch is 465 feet long with 61 feet of rise.
The segment weights vary from 60,000 pounds up to 202,000 pounds. Segments of the new bridge’s three arches have been completed this year.
The new bridge will have two traffic lanes in each direction, but it will also include 12-foot-wide outside shoulders and 6-foot-wide median shoulders.
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“This provides room for shifting traffic as necessary during maintenance and also provides a breakdown lane,” Murphy said. “If cars have to move to the shoulder, they won't cause a traffic backup as is the case now.”
The modern structure is designed for potential future needs in mind, with the capability of having two additional lanes added to it with minimal additional effort.
“You just need to add some floor beam extensions and cast a wider deck, and you're good to go,” Murphy said. “So that's a big improvement. We've also designed it to try and minimize the inspection effort that would be required moving forward and minimize the amount of maintenance that will be required.”
The project’s location influenced many of the design decisions and the construction activities, as well as the overall project limitations.
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The beauty of Hickory Run State Park is well known in the state and was even selected by the Pennsylvania Department of Conservation and Natural Resources (DCNR) and its Bureau of Parks as one of “25 Must-See Pennsylvania State Parks.”
According to Murphy, the new arch bridge was designed with improved aesthetics to enhance the beauty of the natural surroundings. Ultimately, the design helped to ease the process of going through the land transfer approval process.
“With the rocky walls of the gorge, it's natural for an arch — that really makes a lot of sense there. It provides great foundations for the outward thrust that an arch creates,” Murphy said.
“The turnpike really partnered with the DCNR in the state park there to find a solution that was going to work for everyone,” Murphy added.
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The ability to place large cranes and other equipment down into the steep, rocky gorge to erect a girder bridge — a typical solution for this type of situation — would be a challenge and also drive up costs.
Building roads below the bridge required extensive planning for safe orientation. Trumbull needed to access the temporary tower supports, as well as the foundations for the new arch design.
According to Jarred Musser, Project Manager for Trumbull Corporation, it took several months to fully install the access roads to the bottom of the ravine. They used an 80,000-pound hydraulic excavator mounted with a 12,000-pound hydraulic hammer to remove the hard rock.
Trumbull’s solution to the challenging access issue was to keep all the heavy equipment behind the abutments and do their lifting from there.
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Most noticeably, the contractor used two 1,200-ton Liebherr LR11000 Crawler Cranes on either side of the bridge for all of the heavy picks. The structural steel for the arches was lifted by the cranes behind the abutment.
“The arch ribs were designed with that in mind, so we sized them in terms of their weight to make sure that they could be lifted from a crane behind the abutment,” Murphy said. “The segments get shorter as you get out toward midspan to make the weights go down so that they could boom out.”
Each crane had 520 feet of boom and 1.5 million pounds of crane counterweight. Each crane required 70 truckloads and took two weeks to build.
“The installation crane radius for the lifts ranged from 200 feet up to 415 feet,” Musser said. “Several lifts exceeded 85 percent of the crane's capacity and were considered critical lifts requiring additional planning and coordination.”
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“They're some of the biggest cranes I've ever seen,” Murphy said. “They had very large jibs; in fact, they were able essentially to touch booms at mid-span.”
The operators of the massive cranes, crucial to the arch erection, worked in tandem to set the ribs, columns, and floor beams supporting the bridge deck.
Trumbull is utilizing temporary supports for the arch during construction based on anticipated cost to perform the work. Trumbull already owned enough towers and header beams to complete the project.
“The temporary supports are built up of steel towers of varying sizes and heights,” Musser said. “There were 10 individual towers that were spread out over four tower lines, and overall, 850 vertical feet of towers were utilized.”
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According to Musser, two tower lines utilized six individual towers that ranged from 3 square feet to 7 square feet and stood 50 feet tall. The remaining two tower lines utilized four individual towers that were all 7-square-foot towers with heights ranging from 130 feet to 150 feet tall.
Each of the four tower lines required a header beam that was 90 feet in length and 3 feet tall to support the arches and transfer the load into the towers. Each header beam was outfitted with jacking assemblies which would allow for adjustments to the arch throughout construction.
“In total, the temporary supports consisted of over 1 million pounds of steel to support the arch during construction,” Musser said.
According to the PTC, Trumbull is heading up the project's environmental controls, including erosion and sedimentation controls to slow and filter the natural stormwater runoff during construction prior to its entering natural lands or the surrounding waterways, protecting aquatic life.
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One of Trumbull’s temporary tower supports was going to stand within the 100-year flood boundary of Mud Run below the bridge. That required a modification to Trumbull’s environmental permit, taking approximately six months to complete.
“The tower support at this location needed to be decreased in size to reduce the impacts to the stream and thus required additional engineering,” Musser said. “Eight rock anchors had to be drilled into the bedrock below to stabilize this particular foundation.”
With the steel erection nearly complete, the arches are now in place and freestanding. The floor system is being erected on top of that with only minor pieces of structural steel yet to be added. This winter they will be forming the deck, and early in the spring they will be casting the concrete deck on top. The entire project is anticipated to be done by the fall of 2026.
“It has been a wonderful project, both from the design through construction,” Murphy said. “We've had great partners with the PTC, Trumbull, and all of their specialty contractors and erection engineers. It's just been a very good group to work with all around.”
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- Owner: Pennsylvania Turnpike Commission
- General Contractor: Trumbull Corporation
- Construction Manager: STV, Inc.
- Design Consultants: Modjeski and Masters (prime), Benesch, AD Marble, Lotus Environmental, American Geotechnical & Environmental Services
