2013-06-25

Lighting Boston's Tunnels

A project to replace failing fluorescent fixtures with LEDs in 7.5 miles of Boston's automotive tunnels is going to have to begin with a little R&D. Before the Massachusetts Department of Transportation (MassDOT) can select a vendor for the required 25,000 lighting fixtures, those fixtures have to be invented.

"No one makes LED light fixtures for highway tunnels," state highway administrator Frank DePaola told the Boston Herald. Conditions are harsh in the Central Artery tunnel and the tunnels connecting Boston's Logan Airport to the city. The tunnels sit below sea level and must fight seawater incursion, winter and summer temperature extremes, and corrosive salt mixed with water vapor in winter driving conditions.

Interstate 93 Tunnel in Boston, part of the Big Dig.
(Source: Rene Schwietzke from Wikimedia Commons)

What went wrong
These conditions contributed to the untimely deterioration of the original 110-pound (50kg) fluorescent fixtures. One fell into the roadway in February 2011 after all 10 of its stainless steel support clips corroded through. No one was injured on the Sunday morning when the fixture crashed on to the center lane of the tunnel entrance of Interstate 93 North.

Other contributors to the mishap could have been shoddy manufacturing and/or installation during the infamous Big Dig, which ran over schedule and over budget by historic margins. The prime contractor and others settled a lawsuit by depositing nearly $500 million into an account being used to clean up in the aftermath of the Big Dig. This account will supply the $54 million to replace the failing tunnel lighting fixtures. NuArt Lighting, which manufactured those fixtures, sold itself in 2006, and the new owner disclaimed any involvement with the Big Dig.

MassDOT reported the fixture's crash at a press conference 34 days after it happened. By that time, the department had inspected all the other fixtures over active roadways and concluded that galvanic corrosion was to blame. In this electrochemical process, two dissimilar metals oxidize after coming in contact with each other. In this case, the stainless steel clips had made contact with aluminum wireways from which the powder coating had disintegrated. Ultimately, about 6 percent of the 250,000 clips inspected were found to be affected. They were reinforced with plastic ties.

More than a year later, in April 2012, MassDOT announced the project to replace all 25,000 lighting fixtures. The department apparently believed suitable fixtures could be pulled off the shelf, because it said the replacements would begin in a year -- that is, about now.

Permanent replacement, eventually
The news now is that major lighting suppliers are being asked to bid by August to design and supply sample quantities -- a few hundred -- of fixtures that can stand up to the conditions in Boston's tunnels. MassDOT has not spelled out exactly which firms are being invited to bid, but DePaola told the Herald:

We are going to get the GEs, the Sylvanias, and the Philips to build lights that are specific for the tunnel environment. We will pay them to develop these lights... to manufacture, build, and install them to our specs.

Fixtures from the vendors will be tested for a year. Permanent installation won't start until 2016 and will take up to two more years. MassDOT has said that the fixtures will have sealed plastic on the exterior, and that any that fail will be replaced as a unit. The state expects to save $2.5 million from reduced electricity use.

Is DePaola correct that nothing currently on the market would stand up to the conditions in Boston's tunnels? What factors would you worry about if you were designing LED lighting for such an environment?

— Keith Dawson , Editor-in-Chief, All LED Lighting