BRIDGE REPAIR/REHABILITATION FEASIBILITY STUDY

1.0 EXECUTIVE SUMMARY
The existing Mitchell River Bridge (Bridge Number C-07-001 (437)) in Chatham,
Massachusetts, which is owned and maintained by the Town of Chatham, was planned for
replacement under the Massachusetts Department of Transportation (MassDOT) Accelerated
Bridge Program. This project will be supported in part with Federal funding through the Federal
Highway Administration (FHWA) and, therefore, is subject to review under Section 106 of the
National Historic Preservation Act of 1966, as amended [36 CFR 800].
As part of the Section 106 process, FHWA and MassDOT submitted documentation to the
Keeper of the National Register of Historic Places in September 2010 requesting formal
determination of the Mitchell River Bridge’s eligibility for listing in the National Register. The
Keeper subsequently determined in October 2010 that the bridge is eligible for listing in the
National Register. The Keeper found that the existing Mitchell River Bridge was a “rare
example” and “of exceptional significance as the last remaining single-leaf wooden drawbridge
in Massachusetts (and perhaps the entire United States)” and “an exceptionally important part of
the community’s historic identity.” The Keeper’s finding overturned a series of earlier findings
by the Massachusetts State Historic Preservation Officer in 1981, 1985, and more recently in
January, February and July 2010 that the bridge was not eligible for listing in the National
Register.
This study develops and evaluates repair and rehabilitation alternatives for the undertaking that
could avoid, minimize or mitigate adverse effects to the National Register eligible Mitchell River
Bridge, as required under 36 CFR 800.6(a). The results of this evaluation are as follows.
The bridge currently has a National Bridge Inventory (NBI) Sufficiency Rating of 45.9 out of
100 and the bridge is currently classified as “Structurally Deficient” primarily due to the poor
condition of the substructure. The current condition of the timber throughout the bridge varies
from “satisfactory” to “poor” and conditions are conducive to continuing deterioration. Doing
nothing or performing only normal maintenance will not correct the conditions that cause the
bridge to deteriorate. Furthermore, currently available maintenance and repair techniques will
not extend the service life of the timber elements a reasonable duration in this environment.
Although the bridge is currently considered safe, anticipated deterioration in the near future is
expected to reduce the load carrying capacity to a threshold where load restrictions will be
required. Two timber elements already have load carrying capacities less than the required load
capacity and many other timber elements have load carrying capacities only slightly above the
required capacity. Without corrective action, the condition of the timber is ultimately expected
to reach a level where the bridge will be unsafe to carry traffic. Doing nothing or performing
only normal maintenance will not correct the load carrying capacity concerns.
In addition to the current deficiencies in the structural condition, there are functional and safety
concerns that need to be addressed. The bridge would be classified as “Functionally Obsolete”
due to the substandard roadway width, if it were not for the current “Structurally Deficient”
classification. Other functional and safety concerns include substandard curbs and bridge
railings, substandard guardrails and associated end treatments and transitions, substandard
Repair/Rehab. Feasibility Study March 10, 2011
Bridge No. C-07-001 (437) 2 Final Report