INDIANAPOLIS (AP) — State highway engineers plan to take steel samples from two Interstate 465 bridges damaged in a propane tanker explosion to determine whether it is safe to reopen the Indianapolis expressway.

Officials kept the bridges closed on Friday, prohibiting any Interstate 465 traffic from crossing them and preventing southbound I-69 traffic from using the ramp to southbound I-465. The closure on the northeast side of Indianapolis is in the one of the area’s busiest traffic corridors, averaging more than 150,000 vehicles a day.

The state highway department says Thursday’s explosion on an I-69 ramp knocked out one of 45 concrete columns supporting the bridges that will need to be replaced. The steel samples from the bridges will undergo strength testing.