Tyngsborough Bridge Reconstruction

Tyngborough Bridge is a graceful arch bridge over a scenic stretch of the Merrimack River that is currently being refurbished under the Mass Highway Bridge Program.  Originally constructed in 1930, it has an overall length of 656’ but is notable in that it is the longest simple span steel arch bridge in Massachusetts, having a 547’ main span.  It is also one of only 13 known steel rib arch bridges of any configuration in the state and one of only two to utilize an open, braced rib design, the other being the Boston University Bridge.

First slated for repair in 1994, the bridge has not been used since 2006 when a temporary bridge adjacent to the site was completed to facilitate the improvements by relocating vehicle and foot traffic. The bridge is the only crossing point of the Merrimack River north of Lowell and south of Nashua NH and until it’s close, carried and average daily traffic of 22,300 vehicles.     

The project actually consists of two bridges in tandem.   There is a smaller bridge goes over the a railroad freight line that runs along the west bank of the river.  This bridge shares its easterly pier with the westerly end of the large arch bridge that spans the Merrimack.

The railroad bridge is slated for complete demolition and replacement while the large arch bridge is to be a rehabilitated.  The existing sidewalk and bridge deck will be completely removed and replaced along with any rotted stringers and floor beams.  The bridge will also be sandblasted and repainted. It still has its original paint job from 1931.

The bridge carries State Routes 113 and 3A and the intersections at the easterly and westerly approaches to the bridge have long been problems.  Improvements in the form of roadway and signalization were completed to the east of the bridge at Frost Road and Pawtucket Boulevard in 2006 that greatly improved the flow of traffic.  Westbound traffic turning north onto Middlesex Road is still a major problem resulting in all westbound traffic sometimes backing up the entire length of the bridge.   To address this, MassDOT has included in the current bridge improvements plans widen the road on the westerly approach to accommodate a right turn only lane for west bound traffic. The widening will require the construction of an MSE (Mechanically Stabilized Earth) Wall.

After all is done, the existing temporary bridge has to be removed.  When installed in 2006 the whole intersection on the east side of the river was shut down and each section of the bridge was pushed across the river one at a time.  A similar process is being looked at for removing the temporary bridge.  After the span is removed the substantial concrete piers need to be removed from the middle of the river.

Currently the project is in its inital phase and the focus is on relocating utilities, which can often be time-consuming.  Once going at full speed the project should be pretty interesting to watch.

The estimated $17 M project is currently 35% completed with a finish date in 2012.

More images of Tyngsborough Bridge by Karen Westphalen, principal IBeam Images

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