Mass. Department of Transportation crews have completed installation of high-strength support straps on approximately 25,000 tunnel light fixtures in the Boston Big Dig Central Artery tunnels as a safety measure.
The system was developed as a temporary three-to-five-year solution to the tunnel light corrosion issues while engineers evaluate options for a long-term solution, the agency noted in a July 25 press release..
Paul Norton, principal at TranSystems in Boston, which served as transportation consultant for Mass DOT, says the high-strength polymer support strapping wraps around the entire lighting fixture and engages the steel Unistrut structure. “We studied 10 alternatives based on cost, availability and ease of installation and determined this was the best solution,” he says.
Corrosion problems became evident following the collapse of a tunnel light fixture into moving traffic on February 8. No injuries or property damage was reported, but the agency’s operational procedures are under scrutiny after the resignation of a highway administrator following a delay in notifying the public about the incident.
Analysis indicated the fixture failed because of severe corrosion to the aluminum wireway at the locations where the light assembly was attached with stainless-steel clips, according to an April 13 MassDOT report.
On July 14, after the strapping installation was under way, a MassDOT engineer observed a light fixture out of alignment with the clips on the right side of the light not secured, a MassDOT report notes. The fixture was removed immediately and on July 15 re-installed with all new stainless steel clips, it notes. In addition, two high-strength straps were installed as a redundant support measure.
Following the July 14 discovery, MassDOT Secretary and CEO Jeffrey Mullan ordered an acceleration of the installation of the support strapping for all fixtures, the MassDOT press release notes. To achieve this aggressive schedule, MassDOT mobilized additional lifts and electricians, it notes. While the crews worked throughout the tunnel system, an early emphasis was placed on the ramps and entry portal areas.
MassDOT is in discussion with the Federal Highway Administration about the potential use of Central Artery Tunnel Trust Funds for the purpose of providing access to funds to address immediate and interim inspections and repairs of lights removed when the ceiling accident occurred and repair of the corroded wire way clips. The estimated cost is $1.2 million, which would cover some investigation work and temporary repairs.