Middlebury Police Chief Richard Guisti said 60 to 70 people were evacuated from their homes when officials learned of the danger from the hydrogen leak. They were taken to a shelter at the Middlebury Fire Department.
Guisti said the highway would remain shut down for most of the day.
"We're waiting for a company out of Massachusetts to attempt to unload the vehicle before we can have it removed from the site," Guisti said.
U.S. Rep. Rahm Emanuel of Illinois, the fourth highest-ranking Democrat in the House, got stuck in the traffic while traveling from New York to Hartford for a fundraiser for Connecticut Rep. Joe Courtney. Emanuel said he had to get off at Exit 16 on the Southbury/Middlebury line and take Route 188.
"We're just in one long snake-line here," he said in a cell phone conversation with Courtney and reporters.
Highly volatile hydrogen gas was leaking from some canisters of compressed gas on the flatbed truck, which overturned about 5:30 a.m. near exit 17.
The highway was first shut down westbound, but discovery of the hydrogen leak prompted the closing of the highway eastbound from exit 16 and the call for evacuations.
Guisti said the shutdown of the highway meant that local roads in his town and Waterbury were congested almost immediately.
He said Route 64, a main thoroughfare in his town, was almost at a standstill five hours after the truck overturned.
Guisti said state and local police still had their hands full with trying to get traffic around and away from the area and were encouraging travelers to use Route 8 north and south or Routes 6 and 67 to avoid the area.
State police said the driver of the overturned rig suffered minor injuries.