TT (travelling by truck?) (2,3,5)

I believe the answer is:

on the wagon

I believe this is a double definition.

'tt' is the first definition.
(TT can mean teetotal or 'on the wagon')

'travelling by truck?' is the second definition.

(Other definitions for on the wagon that I've seen before include "Off booze" , "Not taking alcohol" , "Not drinking" , "Teetotal" , "Abstaining from alcohol" .)

I've seen this clue in The Guardian.

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.