BOSTON, April 5 (Reuters) - It's a joke in search of a punch line: How many Massachusetts highway workers does it take to change a light bulb? How about 25,000 light bulbs? And how much will it cost?
Five years after Boston completed the "Big Dig" project to relocate 7.5 miles (12 km) of interstate expressways in tunnels under the city - the largest public works project in U.S. history - comes word that the tunnels' light fixtures need a total overhaul.
At an estimated $54 million, the proposed new lighting will cost just a fraction of the roughly $22 billion, including interest, that will finally be spent once the Big Dig is fully paid off in 2038.
The tunnel project took almost a decade longer to complete than originally scheduled and was notorious for cost overruns, design flaws, leaks, worker fatalities and other problems.
Massachusetts Highway Administrator Frank DePaola told a board meeting of the state Department of Transportation on Wednesday that design or manufacturing defects in the original light fixtures pointed to a total overhaul.
The state transportation board and federal officials must sign off on the project, targeted to start in early 2013 and plague local motorists for two years.
Funds are expected to come from the multi million-dollar maintenance fund created with proceeds from a settlement with the original Big Dig contractors.
A single 110-pound fixture fell in one of the tunnels in February 2011. Since then, engineers have fortified lights with plastic ties, but that has been seen as only a temporary solution.
"The existing fixtures continue to corrode,'' DePaola said. "We could have more incidents. For that reason, I think it is best for all of us that we remove the fixtures.''
Good news, though: DePaola said the new LED fixtures would be more energy efficient and longer-lasting than the current fluorescent lights - and could save $2.5 million a year on electric bills. (Reporting By Ros Krasny; Editing by Vicki Allen)