Teacher takes train, overcoming motorway tension (14)
I believe the answer is:
schoolmistress
'teacher' is the definition.
(schoolmistress is a kind of teacher)
'train overcoming motorway tension' is the wordplay.
'train' becomes 'school' (I've seen this before).
'overcoming' means one lot of letters go next to another (some letters are written over others).
'motorway' becomes 'mi' (resembles Ms, English motorway).
'tension' becomes 'stress' (synonyms).
'school'+'mi'+'stress'='SCHOOLMISTRESS'
'takes' acts as a link.
(Another definition for schoolmistress that I've seen is " female teacher".)