Blog of the Pennsylvania State Historic Preservation Office

Ironing Out the Wrinkles: Finding a New Life for the Inwood Iron Bridge

When travelling between Schuylkill and Lebanon County, some may prefer to skip Interstate 81 and take the more scenic route past Swatara State Park.  The park is relatively recent in its formation, created in 1987, and DCNR continues to make infrastructure improvements to provide access to recreational opportunities within the park including biking, hiking, boating, and fishing.

Within the park, the Swatara Rail-Trail follows the former railroad bed of the Lebanon & Tremont Branch of the Reading Railroad and a former feeder branch of the Union Canal. The ruins of five canal locks and a former dam associated with the canal remain. The National Register-eligible Appalachian Trail (AT) passes through the park and at Swatara Creek is carried by the Waterville Bridge, a rare Lenticular metal truss bridge. 

Looking at the front and side of a metal truss bridge.
This photo of the Waterville Bridge from the National Register nomination shows the bridge in its original location in Lycoming County.

The Waterville Bridge was built in 1890 by the Berlin Bridge Company of East Berlin, Connecticut. The bridge once crossed Little Pine Creek in Lycoming County. When it was determined to be too narrow to carry modern day traffic, instead of being demolished it was dismantled and rebuilt to serve hikers on the AT.

Inwood Iron Bridge

Located just downstream from the Waterville Bridge is the historic Inwood Iron Bridge, which once carried Iron Bridge Road across Swatara Creek.  Due to deteriorating condition, the bridge was closed in 2005.

The Inwood Iron Bridge was built in 1899 by Nelson & Buchanan of Chambersburg, agents of the Pittsburgh Bridge Company. The 160-foot-long, pin-connected, Pennsylvania (Petit) thru truss bridge is eligible for listing in the National Register of Historic Places.  In addition to being a rare Pennsylvania (Petit) truss, the bridge exhibits Z-plate floorbeam hangers, a distinctive detail of the Pittsburgh Bridge Company. 

Looking at the side of a metal truss bridge over water.
Inwood Iron Bridge in its original setting over the Swatara Creek.

Pennsylvania Trusses

Pennsylvania trusses were named after the Pennsylvania Railroad; their engineers developed the design in 1875 to carrier heavier loads and to accommodate longer spans.  By design, the Pennsylvania truss is essentially a Parker Truss with sub-struts and sub-ties that stiffen the truss to carry heavier loads.

The Pennsylvania truss continued to be use for railroad bridges through the early 20th century.  The Baltimore truss is also known for its sub-struts and sub-ties, however, the Pennsylvania (Petit) truss has a polygonal top chord giving it a characteristic curvy design.   

Illustration from Trusses: A Study by the Historic American Engineering Record (HAER).

Only thirteen Pennsylvania thru trusses remain in vehicular use in the state. This is half the number recorded just 18 years ago in the 2001 statewide bridge survey

Improving the Crossing

Due to the recent loss of Pennsylvania trusses, and as a requirement of Section 106 of the National Historic Preservation Act, when plans to improve the Inwood Iron bridge crossing were developed, historic preservation was among the most important factors considered.  

Local officials noted the need for firetrucks, buses, and other heavy vehicles at this crossing and looked for ways the bridge could be rehabilitated to accommodate these needs. For the bridge to accommodate a heavier load capacity, many of the truss members needed to be replaced.

Metal truss bridge with three bridge closed signs along entrance.
The Inwood Iron Bridge remained closed for the last 14 years. Photo courtesy of PennDOT.

After much consideration, it was determined that the 120-year old historic bridge could not be rehabilitated to meet modern day traffic without significantly altering the character of the bridge. In addition, the cost of rehabilitation of the bridge to accommodate heavier loads exceeded the cost of a new structure. 

Would this mean the end of the Inwood Iron Bridge?

In order to preserve metal truss bridges that cannot be rehabilitated in their current location to meet vehicular needs, PennDOT and the SHPO jointly administer a metal truss bridge marketing program that focuses on adaptive reuse of historic metal truss bridge as pedestrian or light vehicular bridges on trails or in parks.

The Waterville Bridge was one of the first metal truss bridges in Pennsylvania to be adaptively reused on a trail.

Opening of a metal truss bridge
Waterville Bridge carrying the AT in Swatara State Park.

Could the Inwood Iron Bridge also find an adaptive reuse somewhere within Swatara State Park?

Once it was determined that the bridge could not be rehabilitated to meet the needs of the crossing, the search was on to find a new location for the bridge.  A donation of land by Charles and Charlotte Allwein just downstream from the original crossing provided an appropriate new location. 

Interpretive panel of map
Proposed Interpretive Panel showing location of Metal Truss Bridges in Swatara State Park. Courtesy of PennDOT.

A New Lease on Life

After 15 years of being closed, the Ironwood Bridge will be reopened  in 2020 as a new attraction at the park.  The Ironwood Bridge will be placed near the Swatara Rail Trail and serve as an interpretive display for visitors to learn about the history of water, rail, road, highway, and pedestrian transportation in the area.

Interpretive panel with words and photographs
Proposed interpretive panel showing transportation history of the region. Courtesy of PennDOT.

Once disassembled, the Inwood Iron bridge will be rehabbed, then reassembled at its new location which will include visitor parking, installation of interpretive signage included within this blog, and reuse of the stone from the original abutments. 

Large cranes connected to a metal truss bridge.
On July 9, 2019, the first phase of the project was completed, when the Inwood Iron Bridge was lifted off its abutments and moved to a staging area for disassembly. Photo by Savannah Potts-Krammes.

The bridge will be placed on land, offering visitors a chance to examine structural features usually inaccessible, such as the Z-hangers and pin connections.  The structure will attract visitors from both Swatara State Park and the Appalachian Trail, enabling a larger audience to learn about and appreciate Pennsylvania’s historic metal truss bridges.

Interpretive panel with words and graphics to describe the bridge.
Proposed interpretive panel of the Inwood Iron Bridge. Courtesy of PennDOT.

Plan to be awe-struck when visiting the rehabilitated Inwood Iron Bridge, which is anticipated to be open for visitors by fall of 2020.

Savannah Potts-Krammes was a 2019 PennDOT summer intern working in the Pennsylvania State Historic Preservation Office.  The focus of her internship was on historic bridges, and as part of her internship, she was able to document the lifting of the Inwood Iron Bridge.  Savannah is in her final year at the University of Pittsburgh where she plans to receive her bachelor’s degree in Anthropology and Architectural Studies.   

Two people standing outside in front of a mechanical crane.
Sammantha Johnson (left) and Savannah Pott-Krammes (right) posing in front of the Inwood Iron Bridge after it was moved off its abutments. Photo by Jeremy Ammerman, PennDOT.

1 Comment

  1. Joe Thompson

    The date for completion of first phase of construction is incorrect, it should be July of 2019, not 2010.

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