It’s more than that, though. A car is essentially an elevated trapezoid in cross-section, and you’re sitting near the narrow top of the trapezoid. A Ford F-150 is essentially the same thing, but slightly less tapered and the base is lifted higher up. Either way, you’re squeezed into a lot less than that 6.66’ of width. Private automobile doors are also much thicker than bus doors, there’s space allocated for airbags, there’s stuff on the inside of the door that takes up some of the width.
A bus is essentially a rectangular prism projected all the way back. It uses the FULL 8’4, minus the width of the walls, for every row of seats. So it’s probably more like 3-4’ extra width compared to a car.
Reference
City | Transit Buses have average lengths of 39’2” (11.95 m), widths of 8’4” (2.55 m), heights of 9’10” (2.99 m)
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Most popular “car” in US—Ford F-150
Overall length, 19.3’ ; Cab height, 6.45’ ; Width - Excluding mirrors, 6.66’
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Lane widths in US vary, but should be between 9’ and 12’ (inclusive range for both local streets and highways)
source
Conclusion: Busses are wider than cars, both can fit within driving lanes
It’s more than that, though. A car is essentially an elevated trapezoid in cross-section, and you’re sitting near the narrow top of the trapezoid. A Ford F-150 is essentially the same thing, but slightly less tapered and the base is lifted higher up. Either way, you’re squeezed into a lot less than that 6.66’ of width. Private automobile doors are also much thicker than bus doors, there’s space allocated for airbags, there’s stuff on the inside of the door that takes up some of the width.
A bus is essentially a rectangular prism projected all the way back. It uses the FULL 8’4, minus the width of the walls, for every row of seats. So it’s probably more like 3-4’ extra width compared to a car.