The Big Dig's new southbound configuration made yesterday one of the smoothest Monday morning commutes in recent memory, slashing some trip times nearly in half, officials said.
The average southbound drive time on Interstate 93 from Route 128 to the I-93 tunnel entrance dropped from 35 minutes to 18 to 20 minutes, said Cindy Campbell, director of operations at Smart- Routes, who clocked and watched the morning commute via a series of roadside cameras.
"It's a tremendous difference," she said.
Traffic was so out of the norm that SmartRoutes' staff members kept scanning the southbound roadway, thinking they were missing usual backups.
Tony Parziale, who travels from Andover to Braintree, experienced the time warp.
"Traffic moved along at a faster pace than I am used to," he said.
"That said, Tuesdays and Wednesdays usually have heavier traffic flows, so we'll see what happens the balance of this week. But I remain cautiously optimistic."
Best of all, despite some dangerous lane switching because of the tunnel's new configuration, there were no accidents reported.
"This is a big change," said Jeff Larson, general manager at SmartRoutes, "It's one of those things that in one weekend has really improved things."
It is not the final solution, however, Larson warned.
"There will be times that there will be volume and other incidents that will cause backups," he said.
"No one has ever said that the building out of the tunnel is the magic bullet that will clear up congestion in the city."
There was some confusion caused by the new lane configuration in the tunnel. Where traffic once stayed in the two right lanes, the new configuration places three main lanes on the left, with a single right lane headed to the Massachusetts Turnpike's westbound onramp and Albany Street.
Over the weekend, drivers reported cars and taxis swerving, braking, or even backing up near the new split in the tunnel, fearing they would be forced to get on the Mass. Pike via the right-hand lane.
That's not the case, though there are no signs in the tunnel saying that the right-lane exit later reconnects with I-93 south. The move is designed to force traffic into the three left lanes and avoid congestion near the Congress Street onramp, which is expected to handle as many as 1,500 vehicles an hour during rush hour.
"The message we want to get out is that if you're on 93 south, you should get in the left-hand lanes," said Big Dig spokesman Doug Hanchett. "I think by and large it's the kind of thing people are going to have to adapt to."
The changes began Saturday and mark the last major opening for the $14.6 billion project, which has been troubled by leaks and most recently waterlogged fireproo fing in tunnel ceilings. The changes also include the extension of the carpool lane onto the Leonard P. Zakim Bunker Hill Bridge, a move that ended the carpool lane's jam-prone merge on the lower deck.
The carpool lane extension included the opening of a new fourth lane both on the bridge and into the southbound tunnel.
Other changes include reopening the Congress Street onramp downtown. Pedestrians and commuters said yesterday that it had decreased congestion on the Surface Road and made pedestrian crossings easier and safer.
Finally, the merge of the onramp from the Tobin Bridge to the Zakim Bridge was widened, allowing Tobin traffic to smoothly meld with I-93 south. That pleased Joe Duff of Melrose as he drove down Route 1 to his telecommunications job downtown.
"The extra lane on the Tobin loop ramp works great," he wrote in an e-mail. "Before, things would back up on the loop ramp approaching the Storrow exit, but now with the second lane for the Zakim there weren't any back-ups.
Right now I don't care if [the Big Dig is] a little leaky. I saved five to 10 minutes."
Mac Daniel can be reached at firstname.lastname@example.org