The most common and most likely answer to this crossword clue is the 13 letter word JUXTAPOSITION
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More clues leading to the result JUXTAPOSITION
Buddy explains!

The straight part
We know that "parked close together" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case parked close together = juxtaposition.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does JUXTAPOSITION mean?
JUXTAPOSITION noun- The nearness of objects with little or no delimiter.
- The extra emphasis given to a comparison when the contrasted objects are close together.
- To place in juxtaposition.