A worker with the Delaware Department of Transportation walks behind a warning sign on Interstate 495 near Wilmington, Del., on Tuesday. (Patrick Semansky/AP)

Each day, 90,000 vehicles travel across the Interstate 495 bridge over the Christina River in Delaware, a key bypass that helps drivers avoid the part of Interstate 95 that cuts through downtown Wilmington.

Scratch that: Each day, 90,000 cars and trucks used to travel across that bridge. This week, the bridge was closed because of tilting support columns, a situation that is causing problems for daily commuters and could snarl weekend beach getaways during the busy summer travel season.

The bridge over the Christina River is a key artery for commuters in the Wilmington region and is used by people traveling along the East Coast. It offers a way to avoid taking I-95 through Wilmington, in addition to offering a path to the Port of Wilmington.

The Delaware Department of Transportation shut down the bridge Monday evening. Officials said they received a report about an issue with one of the bridge’s support columns late Friday and sent an inspection crew out Monday morning. Separately, an employee of the transportation department reported Monday that a concrete barrier on the bridge had shifted.

An inspection found that four of the 37 support columns holding up the bridge had tilted, with some shifting as much as 4 percent. The bridge was shut down Monday at 6 p.m., closing it in both directions between Terminal Avenue and 12th Street. It’s unclear when it will reopen. The Delaware Department of Transportation used the word “indefinitely” in announcing the closure, while the department’s chief engineer told the Associated Press that the closure could last for weeks.

“We fully understand the significant regional impact this closure will have on traffic and are working with our regional partners to do what we can to mitigate the situation,” Shailen Bhatt, the Delaware secretary of transportation, said in a statement.

State officials said they will adjust signal timing on nearby roads and deploy Delaware State Police to direct traffic to try and deal with the traffic impact.

It’s unknown what caused the columns to tilt, officials said. At a news conference Tuesday, engineers said it appears that the ground under the columns may have moved. On Wednesday, state officials said it appeared a contractor dumping mounds of dirt next to the bridge may have shifted the ground.

The bridge, which was built in 1974, was last inspected in October 2012 and no deficiencies were found, according to the state’s transportation department. Routine inspections are supposed to occur every two years.

A preliminary analysis conducted by outside experts determined that the bridge can bear its own weight but may not be able to support the amount of traffic that would traverse it, according to the state’s Department of Transportation.

Experts from the Delaware Department of Transportation, Federal Highway Administration, the University of Delaware and engineering firms are investigating the cause of the tilting and working to figure out what to do next. Monitors were installed Monday night to see if the columns continue to tilt.

The director of the Delaware Department of Transportation did not respond to a telephone message Wednesday seeking comment.

Closing the 4,800-foot-long bridge will have a considerable impact on nearby I-95, as drivers who would normally avoid taking I-95 through Wilmington will be forced onto it, adding to that road’s extant congestion. A driver heading from Washington to New York, for instance, can use I-495 to avoid I-95’s Wilmington exits before merging back onto the main roadway shortly before crossing into Pennsylvania. Now, with that alternative removed, these drivers will be forced onto I-95 or side roads.

“There have been a lot of backups,” said Jim Lardear of AAA Mid-Atlantic, which is based in Wilmington, not far from the closed span. “In the mornings, that’s creating a lot of bottlenecks, so I-95 has been backing up both north and southbound.”

Some people heading to the AAA offices in Wilmington said commutes that would normally take 30 minutes took three times as long, Lardear said in a telephone interview Wednesday.

While the issue has largely affected commuters so far, it’s unclear what will happen to vacation travelers, he said. Some travelers won’t be aware of the closure, so this could lead to delays even during periods when there’s less traffic on the road.

“It remains to be seen what’s going to happen on the weekends, when people leave for or return from their vacations,” Lardear said. “I think we could see some complications. It remains to be seen, though.”

Lardear said that drivers planning on going through this region need to allow extra time and be prepared to hit some delays.

This is not the first time a major roadway in this area was completely shut down. I-95 was closed for several months in 2000 for a rehabilitation project. Of course, the new road closure isn’t directly comparable — I-495 was shut down with no notice, while transportation officials spent a lot of time before the I-95 closure in 2000 warning people that it was coming.

Still, that experience does offer an example of how a major traffic shift in this region was managed using a combination of public warnings, signs guiding people to alternate routes and the choosing of a suitable alternate route. (At the time, I-495 was determined to be the best possible alternate route, in part because it didn’t cut through downtown Wilmington.)

Even if the bridge itself is deemed to be stable and reopened, the shutdown highlights a lingering issue when it comes to this country’s bridges: They are falling apart. Tens of thousands are bridges are structurally deficient, which means they aren’t on the verge of falling but they are deteriorating and in need of repairs. A report issued in 2011 found that 70,000 structurally deficient bridges require substantial repairs or replacement.

An eight-lane highway bridge in Minneapolis collapsed during an evening commute in 2007, killing 13 people and injuring 100 others. A bridge segment collapsed in Washington state last year, dumping people and vehicles into the water and resulting in minor injuries.

Meanwhile, Google had already removed the closed Delaware option from its maps as of Wednesday. This is what the Google Earth view of the area looks like, with the shuttered span noted with the red arrow:

(Google Maps)

This is what it looked like in the normal Google Maps view, again with red arrows noting the missing span:

(Google Maps)

And if you attempted to create directions from Washington to New York and tried to manually shift the route over to I-495, this is what it tells you:

(Google Maps)

Heading to this part of Delaware? Dr. Gridlock has guidance and alternate routes.