Crossword Genius

Unpleasant comedown for highway travellers (5,7)

Ross

I believe the answer is:

crash landing

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'unpleasant comedown' is the definition.
The definition suggests a singular noun which matches the answer.

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Another definition for crash landing that I've seen is " Aircraft emergency stop".)

I've seen this clue in The Globe and Mail.
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