What does the cryptic crossword clue "Transport used by some in metropolitan demography (6)" mean?

The definition is "Transport". The wordplay uses a hidden word. Hidden in "transport used by some in metropoliTAN DEMography" The answer is TANDEM.

Transport used by some in metropolitan demography (6)

Guardian Cryptic #29119 | 15 Across | 2023-07-11 flower