The claim that Park and Ride schemes reduce transport emissions is not well-supported by the evidence. In a study of 8 park and ride schemes in the UK, Parkhurst (2000) found that their main effect was to redistribute, not reduce, private car traffic.
Overall, traffic (and kms driven) increased as a result of each P&R scheme, with any reduction in the city centre offset by an increase in traffic in the outskirts. The study further noted that any decrease in traffic in the centre would be offset by induced demand and economic growth if traffic restrictions were not implemented. https://doi.org/10.1016/S0967-070X(00)00006-8