Blasting the horn repeatedly is not a standard signal, but there are standard signals which might apply to a situation like this, for example "vessel not under command", "collision imminent", "vessel reversing", etc.
Don't expect car drivers on the bridge to understand ship signals, though.
Also, how does the driver know what to do? Stopping on the bridge, even well before the point where the ship hit, was clearly the wrong choice. Authorities need to stop new cars from entering the bridge while those on it leave, but that takes more than a handful of seconds to arrange. Unless there are traffic lights, perhaps.
Yes, there's no reason for a ship to attempt to signal drivers on a bridge, nor is there any way for them to do so. Signals are for communicating to other ships.
