Embed motorway scheme within it (7)
I believe the answer is:
implant
'embed' is the definition.
('implant' can be a synonym of 'embed')
'motorway scheme within it' is the wordplay.
'motorway' becomes 'm'.
'scheme' becomes 'plan' (I've seen this before).
'within' means one lot of letters goes inside another.
'm'+'plan'='mplan'
'mplan' put into 'it' is 'IMPLANT'.
(Other definitions for implant that I've seen before include "Introduce" , "Fix firmly" , "Something surgically grafted into body" , "New element in trap" , "Establish" .)