The full time cost of commuting by any transit mode (car, walk, bus, subway) has a fixed time cost and marginal time cost per mile. For some facts about these differentials by mode circa 2001 See Table 3 of this paper . Cars have a low fixed time cost (walk up to your car and turn the key) and a low marginal time cost per mile (you speed along without stoping except for some traffic lights). Cars are expensive to buy and to operate in terms of out of pocket expense. Buses have a high time fixed cost (you must wait for the bus) and a higher marginal time cost per mile (the bus stops annoyingly often to pick up people). But, the bus is cheap in terms of out of pocket expense (25 cents in santa monica!).
Now in the near future, the Baby Boomers will age. There will be more and more older, slightly infirm people moving very slowly to get on and off the bus. This will slow down the bus even more than cars. I fully support the mobility of the elderly using public transit but I don't think that there has been an open discussion about the time costs of loading and unloading this slow moving crew on and off of buses. In terms of the language of economics, the elderly public transit users impose a time externality on the young. If everyone could quickly board, pay and sit down and eventually get off the bus; how much would the time cost of taking the bus change by? In cities with plenty of elderly, I actually think that the answer is a big number.
But for bus to win against car, it must be time effective? To quote Lenin; what is to be done?