Hit a railway bridge at any speed and cause major disruption to trains. Until it's been fully inspected by engineers a (very low) speed limit is applied over it.
A12 reopens after 11-mile tailbacks - East Anglian Daily Times
Inconvenient others with 11 miles of tailback, should be banned from the road for life.
I'd have to say it all depends on the circumstances : if , for example , the driver lost control due to an unexpected event which was outwith his control ( like a tyre blowing out )
Why would a "very low speed" be better than anything else? I would imagine that if the bridge fails when the train passes over it, it will still hurt no matter what the speed.