Officials closed a major Mississippi River bridge between Tennessee and Arkansas for nine hours Monday after a pier under a small approach span settled several inches overnight.

The approach span for the Interstate 40 bridge was still supported by other piers, so the most motorists might have noticed was a slight dip, said Randy Ort, a spokesman for the Arkansas Highway and Transportation Department.

Engineers closed the span just after morning rush hour after finding a pier near the river had settled 3 1/2 inches.

Tennessee Department of Transportation spokeswoman Pamela Marshall said the traffic was moving in both directions on the bridge’s eastbound span. The span had recently undergone improvements while the westbound span carried traffic.

After Monday’s discovery on the westbound side, both spans were closed and traffic diverted to nearby Interstate 55 bridge. The westbound span remained closed Monday night.

Ort said the problem was likely caused by additional, longer pilings being driven to improve the bridge’s stability. While crews worked beneath one half of the bridge, the other half was carrying 35,600 vehicles daily.

River bridges have been under scrutiny across the country since the Aug. 1 collapse of the I-35W bridge over the Mississippi River in Minneapolis killed 13 people. That bridge was undergoing repairs when it fell during the evening rush hour, dropping dozens of cars more than 60 feet into the Mississippi.

Workers have been improving bridges along I-40 to make them safer in case of earthquakes. The New Madrid fault runs through the area.

Marshall said she’s not sure that the Minneapolis bridge collapse played a role in the decision to close the bridge.

“It is a bold stance, considering how busy these bridges are, just to shut them down,” she said. “It is at the front of everybody’s mind. Let’s learn from other situations.”

Judy Easley, 52, of Lepanto, Ark., commutes each day to her job in the clerk’s office at U.S. District Court in Memphis. She said if the traffic was too bad Monday, she planned to say overnight with her daughter, who lives in Memphis.

“If they say 35,000 go across this and 45,000 go across that, now it’s going to all go on one bridge,” she said. “It’s going to be a little hairy.”