First, it would have to be an evacuatable situation, like a hurricane, with enough warning to be effective.

Remember all those school buses that weren't put into use ahead of Katrina? The main parish had about 250 working school buses at the time. I know those buses carry 40-80 people, so if they carried an average of 50 each, that's about 12,000 people. On an evac route, I'm sure that takes up less pavement space than three people per private car (4,100 cars).

I've worked in the transportation industry, and most rigs are topped off with fuel at the end of each run.

So, all you would need would be prearranged drivers for those buses, have them go to predetermined neighborhood, and pick up people. The drivers could automatically take their families if they wanted to. Priority would be given to drivers who didn't have their own cars.

The same concept could apply to city buses.