Just remembered another consideration. When Ken Livingstone introduced free transport for school age children in order to remove cars from the school run, it simply meant a load more children who would have traditionally walked or cycled didn't need to because the bus was free.

Commuters were angry as anything that they couldn't get on the buses any more that were picked with children.

Societies are very different around the world and I'm not sure how much this is factored into ideas that could work really well in some places and not so much in others.