Carriage with frivolous warning to driver behind (5,5)

I believe the answer is:

brake light

'warning to driver behind' is the definition.

'carriage with frivolous' is the wordplay.
'carriage' becomes 'brake' (type of horse-drawn carriage).
'with' is a charade indicator (letters next to each other).
'frivolous' becomes 'light' (I've seen this before).
'brake'+'light'='BRAKE LIGHT'

(Another definition for brake light that I've seen is " Device that signals when a car is slowing".)

I've seen this clue in The Times.

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