Complex sentence: Proof-of-payment (POP) is an honour-based fare collection system which allows all-door boarding, and is used on the 501 Queen, 504 King and 510 Spadina streetcar lines.
Split into simpler sentences: Proof-of-payment (POP) is an honour-based fare collection system that allows all-door boarding. It is used on the 501 Queen, 504 King and 510 Spadina streetcar lines.