Display for announcer reporting traffic tailback? (7)
I believe the answer is:
autocue
'display for announcer' is the definition.
(displayed used by a presenter or announcer)
I don't understand how the remainder of the clue works.
(Other definitions for autocue that I've seen before include "TV prompt machine" , "Newsreader's prompt" , "TV prompt device" , "Newsreader's aid" , "Speaker's aid" .)