Earlier Disaster Led to Focus on Bridge Safety
A mangled car is pulled from the Ohio River beneath the remains of the Silver Bridge. The bridge, which connected Point Pleasant, W.Va., and Kanauga, Ohio, collapsed on Dec. 15, 1967, killing 46 people. Corbis hide caption
It's still unknown why the Interstate 35 bridge over the Mississippi River in Minneapolis collapsed Wednesday night. But in 1967 — the year the Twin Cities bridge opened — another deadly collapse focused public attention on the importance of bridge safety.
The Silver Bridge connected Point Pleasant, W.Va, and Kanauga, Ohio. Built in 1928, it was part of a major transportation route carrying traffic on U.S. Highway 35 (not Interstate 35) across the Ohio River. Its name came from the aluminum paint that covered its span.
The Silver Bridge was a suspension bridge. But instead of the usual wire cables, it was constructed using eyebars made of heat-treated carbon steel. The eyebars were linked together in pairs, like a chain, each connected to the next by a huge pin.
On the afternoon of Dec. 15, 1967, the bridge was jammed with rush-hour traffic. Around 5 p.m., the chain on the upriver side suddenly snapped. The roadway began to tilt, spilling cars into the river 80 feet below. One witness told Time magazine, "The bridge just keeled over, starting slowly on the Ohio side and then folding like a deck of cards to the West Virginia side."
It took about one minute for the Silver Bridge to disappear. Forty-six people were killed; nine others were injured.
According to the National Transportation Safety Board report, the accident was caused by a fractured eyebar. The eyebar had been weakened by a minute crack, formed during casting, which expanded over the years due to corrosion and stress. When it failed, the remaining steel frame could not support the weight of the bridge.
Another factor was overload. The bridge had been designed in the era of the Model-T Ford, which weighed about 1,500 pounds. In the 1960s, cars weighing twice that — and trucks carrying as much as 60,000 pounds. — regularly traveled the Silver's span.
The accident galvanized government scrutiny. President Lyndon Johnson ordered an investigation to determine the safety of the nation's bridges, many of which were more than 40 years old. The survey found that many bridges were rarely, if ever inspected, and were often poorly maintained.
The following year, Congress passed National Bridge Inspection Standards, which require all highway bridges to be inspected periodically. The government also designated funds to repair and replace older bridges. But in recent years, critics have charged that federal and state governments have neglected the nation's infrastructure, failing to allocate enough money for those programs.