An investigation is underway after a dump truck towing a forklift knocked down a 30-foot portion of the pedestrian overpass in Aiea.

The incident shutdown the westbound lanes of Moanalua Freeway for about four hours.

Some students at Aiea Elementary school were close by when they heard a big boom.  A dump trunk towing a trailer with a forklift on it hit the pedestrian overpass at the Aiea off-ramp sending a large piece of concrete into the road just after 1 p.m. Tuesday.

Department of Transportation spokeswoman Caroline Sluyter said the dump truck driver is lucky to be uninjured.

"We never would expect that it was the bridge coming down so we were like oh my goodness, thank God, there was nobody crossing the bridge at the time," said Tia Salave a teacher at the school.

Sluyter said the company that owned the truck did not have a permit to be hauling the load that smashed into the bridge.

"Our bridge engineers did come down. They did take a look at the remaining piece of the bridge, and they did determine that it was safe to remain in place," Sluyter said.

Many people use the overpass to go to the University of Hawaii football games and the swap meet at Aloha Stadium.  Some students at Aiea Elementary also use it to get to school.

Principal Kate O'Malley at Aiea Elementary said, "[Wednesday] morning any child from the housing area, Halawa Heights, they can catch the bus and they are able to catch the bus indefinitely."

The bridge will be closed to pedestrians until it can be fixed.  The DOT spokesperson said they will likely put up safety barriers to keep people off the bridge.