By Al Novack

PHILADELPHIA (CBS) – A driver is dead and three construction workers are injured after an accident on the Platt Bridge.

The driver wasn’t supposed to be on the bridge, because it was closed for construction work, but police say the driver ignored the “bridge closed” signs.

At around 1:25 a.m., investigators say the driver smashed into a piece of construction equipment, knocking three workers to the bridge deck. The driver was pronounced dead at the scene.

The three workers were taken to the Hospital of the University of Pennsylvania, where they were treated for minor, non-life threatening injuries.

The bridge was closed for several hours while crews cleared the scene and authorities investigated the accident.