One of the people who ended up in the water was interviewed on TV ,outside the Hospital where His Wife is recovering.
He stated that the Truck pulling the oversized Load was unable to move to the Left (centre of Bridge) despite having His signals on to do so because another Transport Truck was in the Left Lane overtaking Him!
If what He stated is true the Police should be trying to locate and question the driver of that other Truck.
It seems to Me that other traffic must have slowed to allow the Oversized Load to proceed, other wise I'm sure there would have been many more Vehicles involved.