A self driving bus still faces that capacity issue and is significantly slower. Even BRT is much slower than light rail. Sewer systems have pipes that get wid

A self driving bus still faces that capacity issue and is significantly slower. Even BRT is much slower than light rail. Sewer systems have pipes that get wider the further they go. Road systems have to do the same. The problem is that there are road systems that already have 20 lane highways. Seattle is a small city currently but it's growing and will continue to grow and there comes a point where you'll have to build absolutely massive highways right in the centre to accommodate all the self driving cars and buses.