I love Google Quora, thanks to Chris Judge, retired engineer of 50 yeas in Whaley Bridge, Great Britain, by way of crediting the source
:
If the top deck of a double decker London bus is completely filled with 220 pound people and there’s nobody downstairs, will it become dangerously top-heavy?
"The centre of gravity of an unloaded double-decker Optare bus is very low. It has 16 seats on the top deck. If they were all taken by 16 stone passengers then the extra weight on the top deck would be 1.6 tonnes. The kerb weight of the bus is 7.5 tonnes (7.35 long tons, 8.23 short tons). The bus is 14′5″ high (4.4m) the upper deck is 8′6″ (2.6m) above the kerb. The seats are 3ft (0.91m) above the upper deck The extra tilting moment of having the upper deck full of 16 stone passengers is thus:
(2.6 +0.91) x 1.6 x 1000 x g (9.81) = 55,000 Nm
The mass of the bus is 7.5 x 1000 x 9.81 = 74,000 N
Therefore the extra sitting passengers could tilt the bus 55/74 = 0.733 m (2′5″)
This is insufficient to tip the bus over. In fact the safety factor is 6/2.5 = 2.2
On a double decker bus tip test, it has to withstand a lean-out of 6 feet (1.8m). This is over twice the tilting moment caused by a deck full of sitting 20 stone passengers.
Now if you could get them all to stand up - it might be different."
And that, my friends, is safety at its finest.
And now I finally know why Count Five loved Double Decker Busses. Been wondering ever since 6th grade. Almost wore out the vinyl. Local San Jose band, y'know.