Transport systems that begin each of the three theme answers

Question:

Answer:

SUBWAYS

Length:

Similar Crossword Questions:

Number of times this puzzle's theme word appears diagonally in the grid (to complete the puzzle, shade those words plus the Down answers that begin where they meet)
Shade from the sun that's inserted in this puzzle's theme answers
Word providing a hint to the hidden theme answers
Bit of footwear that appears at both ends of this puzzle's theme answers
Each of the titles in this puzzle's theme answers, e.g.
Shoe additions, and what this puzzle's theme answers contain
What the names in this puzzle's theme entries begin with
Easy, and what this puzzle's theme answers literally are
Secret the theme answers contain
Attendance check, and a hint to the puzzle theme in the first words of the starred answers
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Time to feature any of the three theme answers?
One way to describe the theme answers?
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Org. that has four teams with non-plural nicknames, which begin this puzzle's four longest answers
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Supplements added to each of this puzzle's theme answers
One who can be patched together from the letters added to the theme answers
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What the answers to asterisked clues begin with
What one gets by multiplying the numbers in this puzzle's theme answers
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Agent "embedded" in this puzzle's theme answers
Upright, and what's been removed to form this puzzle's theme answers