A letter or two going by road (5)
I believe the answer is:
lorry
'road' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps there's a link between them I don't understand?
'a letter or two going' is the wordplay.
'a letter' becomes 'l'.
'two going' becomes 'ry' (I can't explain this - if you can you should believe this answer much more).
'l'+'or'+'ry'='LORRY'
'by' acts as a link.
Can you help me to learn more?
(Other definitions for lorry that I've seen before include "From which stolen goods fall?" , "Large truck" , "Industrial vehicle" , "Commercial vehicle" , "Transport vehicle" .)