MNRR Bridge over Rowayton Avenue

Client: CTDOT

Construction Cost: $6.8M

Key Facts:

  • Busiest Commuter Rail in U.S.
  • Bridge Carries 4 Tracks
  • 1,600FT of Roadway Reconstruction
  • Lowering or Rowayton Avenue
  • 450FT of New Retaining Walls

Rated in poor condition due to extensive deterioration in the superstructure, the MNR Bridge over Rowayton Avenue required replacing. The existing 50-foot, open deck steel girder carried four tracks of Metro North over Rowayton Avenue within a constrained area. GM2 provided comprehensive engineering services to replace the structure with a single span, concrete encased steel beam bridge and to improve the existing 11-foot vertical clearance below via 1,600-feet of roadway reconstruction. The scope of work entailed 450-feet of new retaining walls, a new drainage system, utility relocation, and improved access to the train platforms.

Carrying the busiest commuter railroad in the US, staged construction was necessary to maintain serviceability with minimal track outages. GM2 developed a 4-phase staged construction plan allowing for work between active railroad tracks with short term outages. To accomplish this, the design utilized concrete encased steel beams, micropile supported abutments constructed behind the existing stone masonry abutments using a top down approach (excavating as you build starting at the top), and a tied back H-pile lagging system. The layout was critical as the tie-backs for the retaining wall were threaded between the micropiles of the abutments.

This project was completed on-time with no unscheduled impacts to the railroad. Railroad coordination was challenging, as this project was part of a scheduled replacement of multiple bridges along the corridor. Design required extensive coordination with MNR to ensure that the phasing of this project including schedule and time/phase etc. were coordinated across multiple projects. Due to extensive impacts, establishing an accurate estimate for the railroad force account was critical. This was done with extensive coordination with Metro North Railroad and CTDOT. This included identifying flagmen/groundmen requirements, all work items on the railroad and work impacts to signalization and communication that were performed by MNR. This project was completed on-time with no unscheduled impacts to the railroad.