In England, in Bristol and Leeds Town, an experiment is underway: normal Cars can take the bus and taxi fast lane if it carry one or more passengers. It's called "car pooling" and it aims to grow-up the ratio people/car.
Probably this experiment will fail because a great number of families are "nuclear", with one, two or, at maximum, three components. But, at this real moment, the Halls of the two cities speak about a sensible trip-time reduction.
Good luck to Bristol and Leeds.