BOSTON -- Major Big Dig changes await commuters in Boston Monday and the lane shift on Interstate 93 south is already confusing some drivers.

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Gail Huff Reports On Traffic Change

NewsCenter 5's Gail Huff reported that traffic inside the tunnel is being diverted up to the surface because of a lane reduction inside the tunnel. It's one of the most challenging phases of the $14.6 billion Big Dig project and the temporary change is expected to have a significant impact on traffic.

"This will have a catastrophic impact on traffic driving through the city of Boston," said Massachusetts Turnpike Authority Chairman Matt Amorello.

Officials are watching to the extent to which traffic is slowed as a result of the change, which shrinks three southbound lanes down to two lanes just before the entrance to the Dewey Square Tunnel. The third, left-hand lane is diverted at Exit 22 onto a surface street near Chinatown. The two right lanes continue on through the Dewey tunnel. The left lane resurfaces near South Station. Once past a four-block stretch in Chinatown, the diverted surface traffic rejoins I-93 at Kneeland Street.

The traffic diversion is required so that workers can finish work on the Dewey Square tunnel by early 2005. When it's complete, the tunnel will accommodate six lanes of traffic.

More police officers will be on hand to direct traffic, but inside the tunnel, motorists unaware of the change may become confused and slow traffic. An estimated 70,000 vehicles use the southbound lanes of I-93 during an average weekday. Engineers are expecting backups all the way to the Zakim-Bunker Hill Bridge.

"We envision that the backup should not really extend much beyond the Zakim-Bunker Hill bridge and the reason I say that is, not that the demand won't be there, but people will in fact divert to other routes," said engineer Chuck Sterling.

The temporary traffic diversion will last for 10 months.