Is it unhealthy to travel in one? (5)

I believe the answer is:

wagon

I'm a little stuck... Click here to teach me more about this clue!

'is it' is the definition.
I can't judge whether this definition defines the answer.

'unhealthy to travel in one?' is the wordplay.
'unhealthy' becomes 'w' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'to travel' becomes 'go' (synonyms).
'in' means one lot of letters goes inside another.
'one?' becomes 'an' (an apple is one apple).
'go' going inside 'an' is 'agon'.
'w'+'agon'='WAGON'

Can you help me to learn more?

(Other definitions for wagon that I've seen before include "Wheeled vehicle drawn by a horse" , "Vehicle (on which abstainers travel?)" , "Cart; rail truck" , "Railway freight vehicle" , "Wild West trail vehicle?" .)

I've seen this clue in the Evening Standard.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.