Southard Street Bridge Replacement, Trenton, NJ

The new Southard Street Bridge replaced a deteriorating 1920s-era viaduct and improved access and traffic flow to restore a critical intra-city transportation link. The bridge carries motorists and pedestrians over US Route 1 and Conrail tracks in the City of Trenton, NJ. Buchart Horn was the consulting and design engineer from initial planning and design studies through permitting, final scope development, and final design. We also provided traffic and electrical design, survey, mapping, geographic information system, environmental, and construction support services.

The new Southard Street Bridge was designed according to the new Load and Resistance Factor Design (LRFD) specifications created by the American Association of Highway and Transportation Officials (AASHTO). LRFD supersedes earlier design approaches and provides more uniform levels of structural safety, serviceability, and maintainability. The New Jersey Department of Transportation (NJDOT) had just adopted LRFD as preliminary design began, making Southard Street one of the first bridges constructed under the new standard.

The replacement bridge is a continuous steel span 368-foot-long structure with 982 feet of approach roadways. Its superstructure consists of eight welded plate girders, parabolically haunched webs, and a composite concrete deck. Its substructure includes reinforced concrete abutments and piers, all founded on piles.

Local Significance and Public Acceptance

The Southard Street Bridge is a signature project for the City of Trenton, Mercer County, and NJDOT for the following reasons:

  • Integrated engineering and aesthetic design (slender, graceful, contemporary structure with significantly improved pedestrian and motorist safety; longer useful life with lower maintenance; and provision beneath for freight rail, light rail, and multi-purpose pathway).
  • Sensitivity to short- and long-term effects on local residents and businesses: there was no permanent blocking of access or taking of any adjacent homes or businesses throughout the 1,350-foot project length. Additionally, Buchart Horn recognized the importance of the bridge to foot and bicycle traffic and championed a separate, temporary pedestrian bridge during demolition and construction. Despite its added cost, the Federal Highway Administration and NJDOT concurred this was a safety measure and recognition of the needs of local residents.
  • Significant efforts expended to improve aesthetics and achieve historical resonance during the engineering design, including:
    • Concrete parapets with arched cutouts, full-height pylons at each of the four wingwalls, and new lighting to a 1920s design simulate the look of the original
    • Abutments and associated wingwalls are faced with cut original ashlar stone
    • Stone form liner was used on all four concrete retaining walls, which were then mortared to resemble the adjacent original stone
    • Black, angled wire-mesh fencing atop the parapets mitigates vandalism while remaining nearly invisible.

Safety, Social, Economic, and Sustainable Design Considerations

As a new, full-capacity structure with wider roadways, shoulders, and walkways; more substantial parapets; and better lighting enhances public safety. Secondary benefits include:

  • Full load capacity provides shorter route for emergency response vehicles
  • Social and economic benefits from safer travel and shorter delivery routes
  • A safer and more inviting means of crossing the railroad and US Route 1 for pedestrians and bicyclists
  • Long-lasting materials and environmentally-sensitive coatings for sustainability and long-term lower maintenance
  • Plaques from the 1921 bridge cast into the new concrete parapets to memorialize the historic 1921 structure, to the pleasure of local historical organizations

The project has received overwhelming support from residents, historical organizations, and city and state officials.