Many people online allege feeling more 'wobbly' or 'unstable' while seated on the upper deck, than on the lower, and that in an accident, sitters on upper floors are more likely to be ejected out through the windshield even if they're wearing seat belts. Are these allegations true?
Quora distinguishes the physics of the upper deck from lower deck.
The upper deck of bus,in comparison to lower, is high. Due to this fact the torque produced in upper deck is larger than the lower one. One standing in upper deck frequently experiences great push and pulls during acceleration and breaking. One can get injured. So, in fact travelling in upper deck of the bus is dangerous.