A rush-hour crawl that gave vehicles little momentum to slide into the river and a bridge design that minimised falling debris appear to have kept the death toll relatively low in the collapse of a bridge into the Mississippi River.

Authorities lowered the death toll from an interstate bridge collapse to four today, but warned the final number could change as divers search the Mississippi River.

At least seven people died when a freeway bridge suddenly broke into huge sections and collapsed into the Mississippi River in the US during rush-hour traffic jams.