This is exactly what they do in Shanghai and it works. The rails are not for the whole route just long stretches with lots of lights. As far as I can tell they

This is exactly what they do in Shanghai and it works. The rails are not for the whole route just long stretches with lots of lights. As far as I can tell they have a mixed fleet. Electric for ones that are downtown enough to charge and natural gas for busses that are mainly outside the city. Things change rapidly so this may no longer be true.