Anthony Mariano, 59, of Middlebury was operating a piece of heavy equipment, and was hospitalized after the incident on the Route 63 bridge over the Naugatuck River, police said. That span, also known as the Salem Bridge, is being replaced as part of a $24.5 million state project.
He was taken to Waterbury Hospital in critical condition, then transferred by helicopter to Yale-New Haven Hospital.
The affected section of the bridge was closed to traffic at the time of the collapse, and no motorists were hurt.
About 100 feet of the 586-foot bridge buckled and fell as construction crews used a pneumatic jackhammer mounted on an excavator around 6:30 a.m. to break up concrete on the bridge decking, authorities said.
Marinano, who was operating the excavator, had just told his supervisor he was concerned about the bridge's stability and had warned other workers to leave. He was moving the equipment off the bridge when it collapsed, police said.
He works for Southington-based Brunalli Construction, a large construction contractor with five other bridge repair and replacement projects under way in Connecticut. A woman who answered the phone at Brunalli's offices Tuesday said the company had no comment.
Federal and state workplace safety officials were at the scene in Naugatuck on Tuesday.
The federal Occupational Safety and Health Administration fined Brunalli $181,000 last year for safety violations at another state bridge project in Falls Village, one of its other five projects for the state Department of Transportation.
OSHA officials said the company failed to protect workers against falls, drowning and other hazards at the Route 7 job site.
In addition to the Naugatuck and Falls Village projects, Brunalli is the main contractor on bridge projects in Thomaston, New Haven, New Milford, Salisbury and Cheshire. Work on those projects was not expected to be affected by the Naugatuck collapse.
The 49-year-old Naugatuck bridge, which has unconnected parallel portions for two lanes each northbound and southbound, was overhauled in 1986 and is being replaced, transportation department spokesman Judd Everhart said.
It carries about 14,800 vehicles each day, Everhart said.
The portion carrying the southbound lanes was recently fully replaced, so all traffic had been moved over to that new portion as crews worked on replacing the older northbound portion.
The new portion was also closed for inspections after the collapse of the older portion, forcing thousands of drivers to find other routes for their morning commute. It was expected to reopen late Tuesday afternoon or early in the evening, Everhart said.
The collapse occurred as the construction crews removed the concrete decking from the northbound span so they could take down that portion, which runs from land to the first pier and is not over the river itself.
Metro-North Commuter Railroad's tracks are close to the site, so it stopped commuter train service on its Waterbury line early Tuesday and ran buses instead. Everhart said none of the debris appears to have fallen on the tracks.