Engineering Project Case Studies | Erdman Anthony

Improving Traffic Flow at a Southern Pennsylvania Interchange

Interstate 83 Exit 4 in Shrewsbury, Pennsylvania, has experienced significant increases in traffic volumes due to commercial and residential growth in the area. The high traffic volumes are causing vehicles to queue on the off ramps, and the queues sometimes extend onto the interstate, creating safety concerns. In addition, the I-83 bridge over SR 851 is structurally deficient. 

PennDOT embarked on replacing the interchange and bridge to improve safety and capacity and to bring both up to current standards. At this location, PennDOT is building the third diverging diamond in Pennsylvania.

As part of the project, PennDOT is replacing the existing I-83 bridge over SR 851 with a wider structure to accommodate additional lanes. PennDOT is also constructing a diverging-diamond interchange on SR 851, underneath the new structure. The diverging diamond includes two eastbound and two westbound lanes, with traffic signals at the bottom of the ramps. Traffic crosses left and under the bridge, in order to create smoother transitions on and off the interstate.

Another aspect of the project is the Deer Creek culvert, which was replaced with stream improvements, and there was a minor realignment of the creek.

Exit 4 is the first interchange when entering Pennsylvania from Maryland. The project design includes aesthetic enhancements such as  earth-tone dry-stacked stone retaining walls along the bridge. The retaining walls will support red stone flower beds filled with various elegant plants. There also will be red stone flower beds and bioretention basins adjacent to the ramps for the bridge. 

In addition, artwork will be placed on the abutments. It will include a 5-foot by 5-foot prefabricated-metal Liberty Bell sign and a “Life, Liberty and the Pursuit of Happiness” graphic that will be illuminated at night. These beautification treatments were coordinated with local stakeholders during design.

Construction began in 2019 and was completed in late 2021.


Award icon
2022 TQI Partnering Award
Associated Pennsylvania Constructors
Noel Caron, PE
Noel Caron, PE
 717-766-1741 x 5009