The wheels of the bus go round and round

I was on the way home one day, and as usual I will have to take the bus (in addition to the train T.T). Along came a double decker bus. As I scanned my ezlink card and proceeded to walk further into the bus, I happened to glance at the sign which indicates the seating capacity of the bus.

The sign used upper saloon and lower saloon to refer to what I would call the upper deck and lower deck of the bus. Pondering about whether it was possible for the word saloon to mean deck, I snapped a shot of this while trying to look less suspicious at the same time. ;D

For me, saloon means car, the four wheeled type. If this is the meaning of saloon, then it would not really seem right to talk about upper 'car' or lower 'car'. So I explored the OALD, Merriam-Webster and OED to investigate the word saloon.

From the OALD,

sal•oon /slun/ noun
1 (also saloon car) (both BrE) (NAmE sedan) a car with four doors and a boot/trunk (= space at the back for carrying things) which is separated from the part where the driver and passengers sit: a five-seater family saloon

This sense of the word does not seem able to account for the meaning of the upper/lower levels of the bus. Instead, it refers more to the entire vehicle as a whole.

Next, from the Merriam-Webster,

sa·loon
3 British a : parlor car b : sedan 2a —called also saloon car

Hmm.. this seems similar to the previous dictionary entry in the OALD. Taking a look at the OED lastly,

saloon
4. a. A large cabin in a passenger-boat for the common use of passengers in general or for those paying first-class fares;thepassenger cabin of an aeroplane. Also quasi-advb. in to go (etc.) saloon.
b. In full saloon car or carriage: A railway carriage without compartments, furnished more or less luxuriously as a drawing-room or for a specific purpose, as dining, sleeping saloon. Also (U.S.) ‘the main room of a compartment-car or a small subdivision of a sleeping-car’ (Funk's Stand. Dict.).
c. A type of motor car with a closed body for four or more passengers. Cf.SEDAN 1c.

Well, the part in sense 4b which says that saloon could be the 'main room of a compartment-car' does kind of describe the upper and lower 'compartments' of a bus. But I could not find anything in the quotations which had similar meaning to the bus situation here.

Then, looking at the word deck this time, the Longman Dictionary showed the following result:

deck noun

2 ON A BUS, PLANE ETC one of the levels on a bus, plane etc

lower/upper etc deck

I managed to find a seat on the upper deck.

Eddie returned to the flight deck (=the part of an aircraft where the pilot sits).

➔ double-decker (1), single-decker

This fits the required meaning for description of the seating capacity. The OALD also displayed similar results.

deck
noun
2 one of the floors of a ship or a bus: the upper / lower / main deck of a ship We sat on the top deck of the bus. My cabin is on deck C.—see also double-decker, flight deck, single-decker

Therefore, I think it would more appropriate to use deck instead of saloon to refer to the upper and lower levels of the bus since saloon does not have any apparent connection to them.