Trimet's argument that it is cheaper to run light rail than bus is flawed

In terms of operating costs, it is often argued that light rail is cheaper to operate than buses because the fact that the capacity of light rail is so much greater than buses allows for fewer light rail trains to be run than buses operated along a corridor for the same number of passengers. It is true that one light rail train consisting of three sixty feet long cars can carry as many people as four and one-half regular buses. What this means is that assuming passenger load remains constant, a light rail train that has three-car consists operating every ten minutes would need to be replaced by standard buses operating almost every two minutes (six light rail trains per hour = 27.5 standard buses per hour). If there is enough demand along a corridor to operate buses every two minutes, then a light rail train would have lower operating costs than buses.
Unfortunately, with few exceptions - including almost none of the cities shown in the accompanying table - American cities do not have bus corridors that have sufficient demand to operate buses every two minutes. Instead, cities are choosing to operate their light rail lines as often or more often than existing bus service. Replacing a bus route operating every fifteen minutes with even a two-car light rail train operating every fifteen minutes is the equivalent of increasing corridor capacity by three hundred percent (a two-car light rail train is the equivalent of three standard buses). While ridership is likely to increase due to the introduction of trains, it is unlikely to increase by three hundred percent.
Bus vs. Light Rail: Which Is Cheaper to Operate?