The discussions on several recent posts seem to be heading this way. It's worth saying that I tried to cope without a car for several years (10 after leaving school, including 5 in full-time employment). I then gave up, learned to drive, bought a car and now drive more than I should.
The problem with huge and unnecessary car use seems to be in several parts.
1) The way society is (or, more likely, isn't) designed means that people often need to have a car. Visiting family in rural areas, transporting furniture or weekly shopping, etc. I suggest this issue is very difficult to deal with, but its force would be weakened by tackling the others.
2) The cost of a car is heavily split into three categories - initial cost, yearly required stuff (servicing, tax, etc) and incremental cost (fuel, etc) that depends on distance. For convenience, we can split these into owning cost and driving cost - how much it would cost to own the car anyway, and how much it costs to drive it that bit more.
3) Public transport almost always seems to try to compete (if it competes at all) with the total cost of owning a car, whereas to persuade people not to drive, it needs to compete with the driving cost. If I get the bus to my girlfriend's house, it might cost me about £1.50 and take 30 mins or so. If I drive, it costs me about 60p and takes 10 mins. If I walk, it costs me very little and takes about 50 mins. I can't see why a car owner would want to use public transport for that journey. In fact, with things the way they are at the moment, I don't see why a car owner would ever use public transport, except for going somewhere with very poor parking.
4) I used to do a lot of cycling. Again, it's much harder to be motivated when it's competing with the cost of driving rather than owning a car. When I cycled regularly around South Manchester, the main problem was consistent lack of good cycle parking. Yes, there would be places to lock it, and then bits of my bike would get stolen, which was kind of annoying.