If you commute through Boston, chances are you drive through the city’s tunnels. You may not give them much thought unless they end up in the news. Back in February, a piece of concrete fell inside the Prudential Tunnel westbound. And that might have had you thinking about the work that’s done to keep Boston’s tunnels safe.
To give you an inside look at this process, Boston 25 Traffic Anchor Catherine Parrotta ventured into the O’Neill Tunnel southbound with MassDOT shortly after midnight, when that side of the tunnel was fully closed for a tunnel cleaning. This is a process that happens monthly in each of Boston’s tunnels. Catherine was accompanied by Michael McQueen, the Assistant Structures Engineer for the Tunnels. He explained that a variety of work happens during tunnel cleanings, including tunnel washing, flushing gutters, maintaining drains, and doing sign work. In fact, McQueen says signs are routinely checked by both MassDOT and consultants for the usual wear and tear. But on this night, one sign was being repaired after it was hit by an over height vehicle. “What they’ve done is they’ve tightened the backs and sides, ” McQueen explained. “You can see some of them are still bent but they’ll tighten all the additional screws, they’ll put additional clamps up there. They’ll make everything tight so you can still read it and also so that it doesn’t fall down. But some of these may have to be replaced, and so they’ll go back to the manufacturer and then they’ll put those together.”
The signs are washed for improved visibility. The tunnel walls receive a thorough wash too. That process involves one truck spraying soap, three trucks with brushes of different heights, and a good rinse. McQueen explained, “This is part of safety too. the inside of the tunnel is a caustic environment in the sense that the dirt, the oils, the grease, the exhaust, it affects things not in the way you want it to. And it does corrode things.”
The full tunnel closures give crews the chance to look at items like manhole covers and lighting fixtures. MassDOT told Catherine serious issues can be corrected the same night they’re discovered, while others may wait until the next scheduled lane closure. Those closures happen nearly every night. Catherine wanted to know more about the tunnel inspection and repair process. She put in a public records request and obtained tunnel inspection reports from 2024, as well as the tunnel inspection reports for the Pru Tunnel westbound from 2021. She found issues like missing clips on light fixtures, leaks, and cracks were noted frequently in these reports. Catherine sat down one-on-one with MassDOT Highway Administrator Jonathan Gulliver to ask him about that. He told her, “Everything is going to get assessed and looked at. And if it looks like it’s something that needs immediate attention, we’ll give it that immediate attention. Including, you know, sometimes we have sudden emergency bridge closures, or sometimes we have lane takings that we do because we’ve identified something that we have to get in there immediately to address. It happens, we try to avoid it, but that’s the worst-case scenario. In the case of something like a missing butterfly clip, for example. It depends on what the rest of the fixture looks like. If it looks like it’s like this is an isolated thing, the butterfly clip fell off, we have others already holding it up. It doesn’t pose an immediate danger. Next time we have a maintenance crew in there, we’ll address it.”
Gulliver said full inspections of each tunnel happen every two years. The tunnels are inspected in segments, and the whole process takes several months. Full tunnel cleanings like the one Boston 25 observed happen monthly, but only from April to October. It was February when that concrete fell in the Pru Tunnel. Gulliver said that incident led to an immediate tunnel inspection, and changes. “It used to be 10, 15 years ago, you’d have a deep freeze that would last most of the winter. It’s not like that anymore. Now we have more of these cycles where you have a freeze that lasts three, four weeks, things warm up, you get some rain, freezes up again. We’re going to be changing our approach. We’re in the process right now of putting together new procedures. So effectively, if you have a freeze followed by a thaw, we’ll be doing a quick assessment of those joints again to try to avoid that type of situation.”
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