Basically the major problem associated with the collision of double-decked bus lies on the possible overturning of the bus upon collision. The overturning moment is the product of impact force and the difference in the centre of gravity of bus and the height of vehicular parapet. The restoring moment is the product of bus weight and 0.5 times the width of bus.
In fact, owing to the elastic deformation of both the parapet and bus, it is expected that the impact force, and hence the overturning moment may not be larger than the restoring moment for 1.1m high vehicular parapet. Computer simulations have to be conducted to verify if a double-decked bus traveling at a certain speed would roll over the parapet when impacted at a certain angle.
This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.