I forget where I read it, but the cost per km of rail vs buses is pretty appalling.
I suppose that rail has theoretically the advantage in being more reliable. But I do wonder if you could carry the same quantity (outside the subway cities) of passengers on a double lane bus road as a train.
Is the cost of roads handled in that comparison, or are the roads assumed to already exist? (And are the roads being continually expanded to keep up with the induced demand from previous expansion?) If not, then that gives buses an unfair advantage in the comparison.
Also, per kilometer probably isn't the best metric, unless you're building into a low-density area. It would be better to compare the cost per kilometer, divided by the throughput (people/hour).
You need to consider the price of road infrastructure in the total cost of buses. If that is not considered, then you could just as easily just calculate the cost of trains by excluding the rail and signalling-cost (and you would be just as incorrect).
You should certainly consider the buses’ share of the road cost, just like you should consider only the portion of the rail cost that is built and maintained for the commuter usage. If either of those shares is 100%, logically it should be burdened with 100% of the cost. Bus depots, bus maintenance yard, dedicated bus lanes, and bus stop turnouts should all be 100%.
The big advantage of rails is people don't try to drive on them.
Build a dedicated bus lane across the country and everyone will want to use it for their cars, and either do so or bitch to the politicians that they can't.
I suppose that rail has theoretically the advantage in being more reliable. But I do wonder if you could carry the same quantity (outside the subway cities) of passengers on a double lane bus road as a train.