I can understand this happening for lots of reasons....new driver, new route, diversion, driver used to single-deckers only etc.
The bridge only needs to be a centimetre too low...how would a driver know just by looking? (Yes, in an ideal world he would know the EXACT height of the vehicle and that of the bridge...).
All bridges under 16'6 have to have height notices. A standard double decker bus is 14'4 so if it was too tall for the bridge there must have been a warning.
Unless there had been an unavoidable diversion the bus company should have gone through the route with the new driver, the blame could well sit with them.
brainiac, I've been in a few European HGV tractor units and most have the height sign in both metres and feet and inches prominently displayed.
Data has shown that 15% of bridge strikes occur because the driver didn't understand the sign and councils and bridge owners are encouraged to display the sign in both measurements. If I see a sign not displaying the metric equivalent I speak to the highway department or drop them an email. There is no reason for any bridge not to display both measurements.