Dont know about your neck of the woods, but in south London, buses are never empty.
You need frequent, and good quality public transport as an incentive to get people away from cars. Bus use has rises in London in the past 6 years because, well, its much better it used to be. Having frequent services off-peak is important, and I'd argue that they are not running empty.
I rarely catch a bus with more than 5 people on. A study needs to be carried out into the average load of every bus on every route. So many buses take similar routes, often passing through stops at very similar times.
It's probably a little busier further in London, but at the edges it's too much.