I suspect this isn’t as easy as you think. Where I am (Seattle) an empty bus overtaking a full one isn’t really feasible given traffic and lane size considerations.
Well, maybe you should consider banning cars from the city center then. ;-)
I mean, where I live, busses manage to overtake in a one lane for each direction scenario (which is theoretically complicated, but works out in practice as traffics lights can give you chances to use the opposite lane). Nevertheless, what is important is that the front bus waits until the busses behind him have taken the lead. Otherwise there will be very few opportunities to safely overtake the front bus.
I don’t think banning cars would do much, to be honest. Banning cars might actually exacerbate the problem as the folks who would otherwise drive out of convenience now take the bus. Structurally, on many streets there literally just isn’t another lane available for an empty bus to overtake a full one. Getting rid of more cars, while a noble goal imo, won’t fix that.
