Corrosion blamed as light fixture falls on Tobin Bridge; officials promise inspection tonight

By Travis Andersen and Eric Moskowitz, Globe Staff

State highway workers moved quickly Thursday night to inspect light fixtures on the Tobin Bridge after one fell onto the highway earlier in the day. Officials assured motorists that the route used by thousands of commuters daily is safe for travel.

The light fixture, which weighs between 10 and 15 pounds and is about the size of a small television, fell about 15 feet from its bracket underneath the Tobin’s upper deck onto an ­approach ramp to Route 1 in Charlestown. It did not appear to have hit anything. A state trooper spotted the fixture on the road around noon Thursday, but it was not clear when it came down.

“It is very lucky that it didn’t strike a vehicle when it fell,” said Frank DePaola, the state highway administrator .

The light fixtures are around 20 years old and were due to be inspected later this year, transportation officials said. DePaola said the likely cause was corrosion in the fixture’s support bracket.

There are as many as 20 such fixtures on the bridge, ­DePaola said, but no others ­appeared to be in danger of falling based on a visual inspection Thursday afternoon.

State highway workers began a physical inspection, which involved grabbing each light to see whether it was firmly attached, around 10 p.m. Thursday.

“Any defective lights will be removed immediately,” DePaola said, adding that replacement would cost about $1,000 per fixture.

He said the fixture’s connection to the overpass may have been weakened by high winds from the storm on Wednesday, and the corrosion on the bracket may have been exacerbated by the bridge’s proximity to saltwater.

Officials said the spotlight-style fixture differs considerably from the one that fell in the Thomas P. O’Neill Jr. Tunnel in February 2011, triggering an inspection that revealed that thousands of flawed fixtures in the Big Dig tunnels needed to be replaced. The state did not disclose that problem for more than a month.

The O’Neill fixture that fell was much heavier and was used as a primary light source for the tunnel. The smaller fixtures on the Tobin are used as secondary lighting, said Cyndi Roy, a spokeswoman for the Massachusetts Department of Transportation.

Asked if motorists should feel safe in light of Thursday’s light collapse, DePaola said, “people should feel confident that the highway division [is] out there” maintaining the state’s bridges.

DePaola said the inspection on Thursday night will not ­affect the Friday morning commute. His department intends to release additional details about the light failure Friday morning.

The 2¼-mile Tobin was built between 1948 and 1950 and carries around 45,000 vehicles outbound from Boston each day. However, inbound traffic is much lighter — fewer than 30,000 vehicles daily — as drivers have to pay a $3 toll.

The hulking green bridge is considered to be in fair condition by state engineers but is currently undergoing major repairs.

Highway officials just embarked on a 2½-year, $44.8 million project to clean and paint the Tobin, which will help preserve the steel and prevent rust as well as address older lead paint, said Roy.

One lane in each direction has been closed to accommodate the construction.

Roughly $40 million in additional deck repairs, sand blasting, and spot painting are slated for the next few years.

DePaola said the construction work had nothing to do with the fixture collapse, which occurred about 1,000 feet from the work site.

Like all bridges owned by the state Transportation Department, the Tobin receives a biennial inspection that looks at structural elements as well as attachments, such as lights, Roy said. It received a clean bill of health during its 2010 inspection, she said. The Tobin is not one of the 502 state-owned bridges dubbed structurally deficient, meaning those bridges are still considered safe but have deteriorated to the point of needing repairs to stave off weight restrictions and closure.

Travis Andersen can be reached at tandersen@globe.com. Follow him on Twitter @TAGlobe. Eric Moskowitz can be reached at emoskowitz@globe.com. Follow him on Twitter @GlobeMoskowitz.