Bus vs. Rail

I am going to punch the next feckless moron to conflate the costs of mixed-traffic bus system with a dedicated running-way rail system. It's simply not an apples to apples comparison, in either cost or quality of service. One is a Buick, and the other is a Cadillac. While both enjoy the same potential ridership (in terms of the built environment), there is a vast difference in performance. To call out one aspect in particular: system delay. As the Transit Capacity and Quality of Service Manual is good enough to point out:

This point of view also includes measures of
facility capacity in terms of the numbers of transit vehicles or total vehicles that can
be accommodated. Because transit vehicles carry passengers, these measures also
reflect the passenger point of view: passengers on board a transit vehicle traveling at
an average speed of 12 mph (20 km/h) individually experience this same average
travel speed. However, because these vehicle-oriented measures do not take
passenger loading into account, the passenger point of view is hidden, as all vehicles
are treated equally, regardless of the number of passengers in each vehicle. For
example, while a single-occupant vehicle and a 40-passenger bus traveling on the
same street may experience the same amount of delay due to on-street congestion
and traffic signal delays, the person-delay experienced by the bus is 40 times as great
as the single-occupant vehicle.

It's not a question of bus versus rail, (as many BRT projects are empirically proving) but a matter of right of way. Dedicated running-way provides value, but at a price. Whether the value is worth the price depends on the project, not the technology.