Trunk route going north via Longleat Road (5)

I believe the answer is:

aorta

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

'trunk route' is the definition.
(I've seen this before)

'going north via longleat road' is the wordplay.
'AORTA' is hidden backwards within the letters.
However, I am uncertain how the hidden word is indicated.

Can you help me to learn more?

(Other definitions for aorta that I've seen before include "vital transporter" , "One leads from heart" , "Great artery in body" , "Large blood-vessel" , "Body's main artery" .)

I've seen this clue in The Sun and The Telegraph.

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