On most rail bridges there are bridge strike signs advising the public who to contact if the bridge is hit by a vehicle. A number of these say 'contact Network Rail on xxx', some still say 'contact Railtrack' but some say 'contact the Rail Authority'. Who was this final term intended to refer to? Does it suggest that a number of the bridge strike signs were put up in the period between end of Railtrack/start of Network Rail and so it was a holding phrase that was used or is there some other explanation?