BOSTON -- There's more bad news for Boston drivers Monday. Another Big Dig tunnel was closed over the weekend out of concerns about its safety. While not everyone uses this major tunnel, its closure has a big impact on city streets and beyond.

The Seaport district is where the latest closure is. It's a quarter-mile-long ramp that connects Interstate 90 west to Interstate 93 north and south -- exits 24 and 25.

Drivers can still take exit 25, but they will no longer be able to connect to the expressway.

The detour is expected to send about 6,000 vehicles onto local roadways.

NewsCenter 5's Gail Huff reported that at least 40 suspect bolts were found in an additional tunnel ramp over the weekend.

"It's really a connector tunnel which connects the Ted Williams Tunnel to I-93 south and northbound," Gov. Mitt Romney said.

The latest closing will send thousands more vehicles onto local roadways, which is not good news for local residents.

"We anticipate that the impact could be significant and of course, with any event like these, we urge people to take public transportation, carpool or maybe even travel at alternative times," said John Carlisle of the Massachusetts Highway Department.

The detours are well-marked, but officials are warning Boston commuters to prepare for the long haul.

"For the entire system to be repaired and safe is probably going to take at least a couple of months, and perhaps longer," Romney said.

At the Boston Chamber of Commerce, officials were concerned that tourists might shy away from the city because of the difficulty of accessing Logan International Airport. So far, however, downtown businesses were not seeing a significant impact.

"If you've been around the city ... at Faneuil Hall or Newbury Street, there's still a lot of people coming into the city, shopping, eating and taking in the sights," Office of Arts and Tourism spokeswoman Julie Burns said.

Neighborhoods were expected to see a lot more traffic on the surface roads, with delays mainly affecting motorists trying to get into the city from the airport.

NewsCenter 5's Jim Morelli reported that the latest stretch of roadway was closed because a hydraulic machine brought in over the weekend to test the strength of bolts that hold up heavy ceiling panels in the tunnels indicated many were unsafe.

Last week, several 3-ton ceiling panels in a I-90 connector tunnel eastbound broke loose, smashing down onto a car carrying Milena Del Valle, 38, and her husband Angel, 46. Milena Del Valle was killed instantly. Her husband escaped with minor injuries. The tragedy sparked major state and federal investigations into the safety of all the Big Dig tunnels and the entire metro-Boston highway system.

"What has happened, last Tuesday, was not an anomaly but a systemic failure in the fastening system," Romney said.

The governor said there was no imminent danger but he did release alarming inspection results on the bolts used to fasten the ceiling tiles in the Big Dig tunnels, particularly for those in the exit ramp on I-90 westbound.

"Now, with the full inspection complete, it turns out that instead of having 20 bolts of interest on that ramp there are more like 40," Romney said.

The concern is that the bolts may be coming loose and the epoxy glue fastening system is in the midst of widespread failure. In all, about 360 trouble spots have been identified and it's not just the ceiling tiles that are in danger of falling down. Romney said part of the tunnel ventilation system is attached using the same epoxy bolt system.

"There's also in Ramp A, there are three large jet fans, they look like jet engines, they're hung from the ceilings, they're part of the overall ventilation system. Those are also held up with epoxy bolts and they show signs of movement as well," Romney said.

SmartRoute's Cindy Campbell reported that early on Monday the Sumner Tunnel was relatively clear, but volume was increasing on Route 1A coming from the Ted Williams tunnel. The Callahan Tunnel backed up early and was backed up all the way to Medford just after 6 a.m. There were also delays on Storrow Drive and traffic was backed up at the Longfellow Bridge.

Eastbound on the turnpike was closed and all traffic was being detoured off exit 24 to Route 93 northbound. There are two choices once commuters exit the O'Neil tunnel. They can take exit 23 up to Government Center and negotiate surface streets to get to the Callahan Tunnel. They can take Exit 26 that leads to Storrow Drive and Leverett Circle, which was also congested.

Westbound was closed at Exit 25 and there was no access to I-93, so drivers must detour through surface streets to get to either 93 north via Atlantic Avenue or I-93 south via a frontage road.

According to the Boston Police Department, the following detoured route will be in effect immediately until further notice:

All traffic from I-90 West/The Ted Williams Tunnel must take Exit 25 towards South Boston.

To access I-90 West and I-93 South, take a left on Congress Street, left on West Service Road and right onto the South Boston Bypass Road.

To I-93 South take a left onto southbound Frontage Road to the I-93 South on-ramp. To I-90 West take a right onto northbound Frontage Road to the I-90 West on-ramp.

To access I-93 North take a left on Congress Street, right on East Service Road, left on Seaport Blvd. to the I-93 North on-ramp to Atlantic Avenue.