The standard test was to fill the top deck with sandbags representing the weight of a full load of passengers and to leave the lower deck empty.
But buses can still fall over if provoked sufficiently.
Accident at the junction of Burnham Road and Slough Road,
Beaconsfield, Bucks at 14.00 on 4th July 1964.
The bus is an RT of London Transport.
The accident caused one death and 39 injuries.