Reliable public transport could be an option! What’s that saying about busses, you wait for ages for one to come along then three turn up at once!
The problem with arguing that if buses were more reliable people would leave their cars at home, is that buses are unreliable (as andrewbowden points out) at peak times when the traffic is heavy. So people will have to leave their cars at home first in order for the buses to become more reliable. It's classic chicken-and-egg!
And let's be honest, buses are not the ideal solution. Look at what has happened at Hazel Grove, where there was a huge investment in that park-and-ride car scheme, intended to persuade motorists to leave their cars and catch a 192 bus into Stockport or Manchester. It just hasn't worked, and the car park is mostly empty (and so are the buses), because people simply don't want to go on a bus if they can help it. But the big 'double-deck' car park at Hazel Grove station is full, because trains are quicker and more reliable than buses, so people will use them
It puzzles me why the car park across the road at Marple station can't be extended - there's a huge area of unused rough grass at the back. If there were more capacity there, surely more people would park there and use the trains.