Crucial bridge along East Coast interstate system closes indefinitely over leaning columns

The answer as to why a bridge on a major East Coast interstate is tilting could lie deep underground.

The Interstate 495 bridge in Wilmington, Delaware, which normally carries 90,000 vehicles a day, was closed Monday after four pairs of support pillars were found to be tilting. Officials don't know when it will reopen.

Preliminary findings indicate the ground underneath the pillars has shifted, but engineers and workers in hard hats are using shovels and high-tech sensors to try to figure out the extent of the problem.

Meanwhile, the 11-mile-long I-495 bypass from south of Wilmington to the Pennsylvania line remains closed indefinitely, with motorists being shunted onto nearby Interstate 95 through downtown Wilmington, further overloading one of the most crowded arteries in America.