They are marvels of steel and concrete, engineering feats that millions of drivers speed across every day.
But Wednesday's collapse of a Minneapolis bridge that left at least four people dead and many more missing is a grim reminder of how fragile these seemingly secure structures can be. More than a dozen major bridges, overpasses and highways have collapsed in the United States and around the world in the last 40 years, killing dozens of motorists.
Earlier this week, a highway overpass under construction in Oroville, Calif., collapsed, crushing a delivery truck and seriously injuring a construction worker who fell 50 feet.
In April, a section of freeway that funnels traffic off the San Francisco-Oakland Bay Bridge melted and collapsed after a gasoline tanker truck overturned and burst into flames, injuring the truck driver.
Fourteen people, including a 3-year-old girl, were killed in May 2002, when a 500-foot section of a bridge spanning the Arkansas River in Webbers Falls, Okla., collapsed after a barge ran into one of its supports.
In September 2001, Texas' Queen Isabella Causeway gave way after a string of barges driven off course by currents crashed into a bridge support. Eight motorists died when their vehicles plunged 85 feet into the channel. Because the causeway is the only bridge connecting the popular beach destination South Padre Island with the mainland, the disaster had a huge economic impact on the area.
In April 1987, 10 people were killed when a bridge on the New York State Thruway near Amsterdam, N.Y., gave way.
One of America's most deadly bridge breakdowns occurred in 1980, when a 1,000-foot section of the Sunshine Skyway Bridge in Florida collapsed after a freighter struck it during a storm. A Greyhound bus and several cars plunged 150 feet into Tampa Bay, killing 35 people.
While the Sunshine Skyway Bridge tragedy may be the worst U.S. bridge accident in recent memory, it was not as deadly as the 1967 Silver Bridge collapse. In December of that year, the eye-bar chain suspension bridge collapsed into the Ohio River at the height of rush hour, carrying 31 vehicles and 46 people with it.
Several bridge collapses outside of the United States have been even more deadly. In March 2001, a pillar on a 116-year-old bridge in Lisbon, Portugal, gave way, causing a tour bus and two cars to plunge into the Douro River and killing more than 50 people.
Eleven people died in October 2001, when two trucks collided in the 10-mile-long Gotthard tunnel, which cuts through the Swiss Alps. Fire spewing thick black smoke delayed rescue attempts and an explosion caused a 100-yard stretch of ceiling to collapse on trapped cars.
After a high-speed train derailed in Hanover, Germany, in June 1998, cars flipped off the tracks, causing an overpass to collapse and killing 101 people. Bodies were pulled from the wreckage and found near the tracks among shredded seats and luggage.
In Quebec in September 2006, five people died and six were injured when a more than 60-foot stretch of an overpass collapsed, sending cars tumbling and crushing the vehicles below. It took workers more than 24 hours to reach two trapped cars in the debris; they were flattened to knee height.
In 1995, an estimated 50 people were killed when a bridge collapsed under heavy rain near Aflou, Algeria, and in the fall of 2005, six people were killed when a section of a highway bridge collapsed and plunged into a ravine in southern Spain.
According to the Center for International and Strategic Studies, more than a quarter of the country's 600,000 bridges are structurally unstable. A 2005 federal report stated that Minneapolis' Interstate 35W bridge, built in 1967 and supported by a single steel arch, was structurally deficient and may need to be repaired.
The fact that 27 percent of U.S. bridges are unstable "does not necessarily mean that any is near imminent failure," Casey Dinges, the managing director of external affairs for the American Society of Civil Engineers, said on "Good Morning America" today.
"Once a bridge has been designated to have problems, we keep a close eye on it," Dinges said.
Dinges said that despite this long history of bridge breakdowns and the ongoing tragedy in Minneapolis, nervous commuters "should not be overly concerned" about their local bridges collapsing. "People getting in their cars this morning should not be fearing for their lives," he said.
In a news conference today, U.S. Secretary of Transportation Mary Peters emphasized that bridge collapses like the one in Minneapolis are a relative rarity and she pledged to make sure bridges across the country stay safe.
"Bridges in America should not fall down," she said. "We need to get down to the bottom of this and that is absolutely my top priority."
Reuters and The Associated Press contributed to this report.