Prominent means to deter a career in transport? (5,4)
I believe the answer is:
speed bump
'prominent means to deter a' is the definition.
I can't judge whether this definition defines the answer.
'career in transport?' is the wordplay.
'career' becomes 'speed' (career can mean to run or rush around).
'in transport?' becomes 'bump' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'speed'+'bump'='SPEED BUMP'
Can you help me to learn more?
(Other definitions for speed bump that I've seen before include "Traffic-calming device" , "Sleeping policeman" , "Sleepng policeman" , "Traffic-calming measure (B, not H)" , "traffic checker" .)