Page "Big Dig" Paragraph 37

In March 2011, it came to light that senior MassDOT officials had failed to disclose an issue with the lighting fixtures in the O ' Neill tunnel.

In early February 2011, a maintenance crew found a fixture lying in the middle travel lane in the northbound tunnel.

Assuming it to be simple road debris, the maintenance team picked it up and brought it back to its home facility.

The next day, a supervisor passing through the yard realized that the fixture was not road debris but was in fact one of the fixtures used to light the tunnel itself.

Further investigation revealed that the fixture's mounting apparatus had failed, due to galvanic corrosion of incompatible metals, caused by having aluminum in direct contact with stainless steel, in the presence of salt water.

The electrochemical potential difference between stainless steel and aluminum is in the range of 0. 5 to 1. 0V, depending on the exact alloys involved, and can cause considerable corrosion within months under unfavorable conditions.