What number is this bus?
'Numero' — 'NU-me-ro'. Three syllables; stress on the first.
Use when a bus arrives but the display panel is unclear, dirty, or off, and you need to confirm the route number before boarding.
'Che numero ha' literally means 'what number does it have'. An alternative is 'Qual è il numero?' (What is the number?). Both are completely natural. The question is directed at the driver or fellow passengers.
È il trentadue?
Is it the 32?
Direct confirmation when you think you know the number.
Quale linea è?
Which line is it?
Equivalent question using 'linea' instead of 'numero'.
Questo va verso...?
Does this one go towards...?
Skips the number and asks by direction instead.
Italian bus numbers are always cardinal numbers, never letters alone (unlike in some countries). Routes are sometimes supplemented by letters indicating variants, such as '40 barrato' (40/) for an express variant.