Cheaper yes, but buses (even bus rapid transit, or BRT) don’t scale as well to large numbers of passengers. This 2009 study compares BRT, regular buses, light rail, and mass rapid transit (MRT), and finds that MRT has the lowest cost per thousand passenger-mile:
In concluding, the author concludes that, on average, “BRT can outperform LRT in providing a moderate to high level of service capacity at a moderate level of capital and operating costs in neighborhoods with moderate population and job densities.” While MRT are the most expensive to build, they can achieve over five times the capacity of BRT or LRT, and are associated with the largest positive impact on property values in the vicinity of stations.
Also you have to actually implement BRT to reap most of the benefits, which means no sharing lanes with other vehicles.
Cheaper yes, but buses (even bus rapid transit, or BRT) don’t scale as well to large numbers of passengers. This 2009 study compares BRT, regular buses, light rail, and mass rapid transit (MRT), and finds that MRT has the lowest cost per thousand passenger-mile:
Also you have to actually implement BRT to reap most of the benefits, which means no sharing lanes with other vehicles.