Is this your crossword clue?
"pileup" is also used as a crossword clue. If that's what you saw, the answer is often accumulation (12 letters).
Definitions
multiple collisions of vehicles
Word origin
Deverbal from pile up.
Source: Wiktionary, CC BY-SA 4.0
Used as a crossword answer1 curated clues
01“Traffic jam cause”6 letters
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