Complex sentence: Coinciding with the launch of the new vehicles, the 510 Spadina became the first full-time Proof-of-payment (POP) line, which allows passengers with POP to board at any door of the streetcar.
Split into simpler sentences: Coinciding with the launch of the new vehicles, the 510 Spadina became the first full-time Proof-of-payment (POP) line. This allows passengers with POP to board at any door of the streetcar.