Components that cause corrosion are present: the electrical current in the light, the saltwater splash off trucks and clips clamped tightly to the fixture’s painted surface. “Whenever there is a bare spot, corrosion gets intense,” he says. “The powder-painted surface looks fine, but the clips could be scraping the paint,” he says. “If you’re counting on paint to be a barrier between two dissimilar metals touching each other, that could lead to corrosion,” he says.

The fallen light fixture was near the entryway of the tunnel, indicating the problem is not widespread. MassDOT likely will change its lighting specifications, he adds.

In July 2006, several 4,600-lb ceiling panels broke free in another portion of the tunnel system, crushing a passing car and killing the driver, 38-year-old Boston resident Milena del Valle.

The latest estimate of the Central Artery Big Dig project is around $15 billion, after an initial cost estimate of between $2 billion and $3 billion. Completed in 2007, it is considered the most expensive highway project in U.S. History.