By Kevin Murphy
(Reuters) - A major bridge that carries freeway traffic over a river in Green Bay, Wisconsin, was closed indefinitely on Thursday after it suddenly developed a sag that was described by one policeman as resembling a roller coaster.
A 400-foot (122-meter) span of the Leo Frigo Memorial Bridge that carries Interstate 43 traffic over the Fox River in Green Bay was left with a rippled surface after a bridge pier settled 22 inches on one side and 27 on the other, officials said.
"It's something akin to a roller coaster, actually," Lieutenant Karl Ackermann of the Green Bay Police Department said, describing the dip in the road.
Wisconsin Department of Transportation officials told a news conference that the settling of the bridge pier had caused the sag, and that there has been no further settling since the first measurements on Wednesday morning, they said.
"We don't see any movement," said Bill Dreher, an engineer and structures design chief for the state's Department of Transportation. "We are pretty confident at this time that it's stable."
State and federal engineers and inspectors were investigating why the 82-foot (25-meter) tall pier settled.
The problem was reported by a motorist early on Wednesday morning before the rush hour, Ackermann said. Police closed the bridge for safety reasons and no accidents or injuries were reported, he said.
The bridge is commonly used by large trucks and other traffic as a bypass around downtown Green Bay, Ackermann said, and carries about 40,000 vehicles per day.
Shipping on the Fox River below the bridge continued uninterrupted on Thursday, officials said. The section of the bridge directly above the river is a separate unit from the damaged span and they are connected by hinges, Dreher said.
Built in 1980, the bridge will be closed for an indefinite period to determine the cause of the problem and whether other piers have also settled, officials said. It was last inspected in 2012 and was not among 60 bridges in the state listed as deficient.
The surface of the Wisconsin bridge after the settling looks somewhat similar to the freeway bridges in San Francisco after the 1989 earthquake.
In May, a 160-foot (48-meter) section of the Interstate 5 bridge over the Skagit River about 55 miles north of Seattle collapsed after being struck by a truck carrying an oversize load. Two vehicles behind the truck plunged into the frigid waters below and three people were plucked from the water with minor injuries.
In 2007, an Interstate 35 bridge in Minneapolis also collapsed, killing 13 people and injuring 145. A design flaw was blamed for that collapse.
In 2002, 14 people died when a barge plowed into an Interstate 40 bridge over the Arkansas River near Webbers Falls, Oklahoma, and a section of it collapsed.
(Reporting by Kevin Murphy in Kansas City, Missouri; Editing by Tim Dobbyn, Cynthia Johnston and Lisa Shumaker)