What does the cryptic crossword clue "Scotsman, the first person that's regularly driven over (7)" mean?

The wordplay uses a charade (building blocks). MAC (synonym="MAC") + ADAM (synonym="ADAM") = MACADAM The answer is MACADAM.

Scotsman, the first person that's regularly driven over (7)

Guardian Cryptic #29256 | 16 Down | 2023-12-18 flower