Why MassDOT dismissed the idea of a Cape Cod tunnel

Officials say tunnels pose a lot more challenges compared to bridges, even if people keeping asking.

BOURNE, MA - 5/06/2015: The Sagamore Bridge , Bourne Ma., Cape Cod   (David L Ryan/Globe Staff Photo) SECTION: METRO TOPIC
The Sagamore Bridge crossing the Cape Cod Canal. –David L. Ryan / The Boston Globe

The idea of a Cape Cod Canal tunnel may be a joke for most local residents. But not for all of them.

As the Massachusetts Department of Transportation conducted their multi-year study on how to best address the area’s seasonal traffic woes, officials couldn’t escape the idea of making it a reality. With traffic backups around the two narrow, aging bridges a summertime regularity, why couldn’t drivers have the option of sneaking under the canal instead?

That’s the question many Cape Cod residents were seriously asking.

According to MassDOT documents, the concept of a car tunnel — as well as a tunnel under Buzzards Bay connecting Marion and North Falmonth — was regularly submitted as a potential traffic solution by attendees during their public meetings, even as department officials repeatedly insisted that the idea was impractical.

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MassDOT officials even addressed the issue in the final draft of their report released this week, citing the high cost of constructing and maintaining a tunnel, compared to a bridge. The tunnel proposal was “not advanced,” in favor of improving existing infrastructure, like local ramps and rotaries (the U.S. Army Corps of Engineers is also expected to soon decide if the Bourne and Sagamore bridges will need to be replaced).

Judi Riley, a MassDOT spokeswoman, told Boston.com the tunnel option was an early stage consideration that was removed from more detailed analysis by the working group of local and state officials, after their initial examination found it would have “substantial impacts” to local properties and the environment.

As MassDOT officials explained during two public meetings in 2016, the canal alternative would present “many challenges.” Due to local topography, it would need to be much longer than a bridge. It would also require “substantial ventilation equipment and structures,” as well as a major study to assess its environmental impact. Additionally, they noted that it would be difficult to accommodate bicycles or pedestrians in tunnels.

In total, officials said the construction cost of a tunnel would be at least double compared to a bridge.

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Still, according to the notes for the two meetings, the last comment of both sessions came from someone asking about tunnels. In each case, MassDOT officials reminded them that they were no longer being considered.

So for now, the idea of Cape Cod Canal tunnel will remain confined to the bumpers of cars, as they wait to cross the Bourne or Sagamore bridge.