_delirium pointed out the regulation that allows Sprinter and San Diego Trolley to get around the weight requirement in this comment: http://news.ycombinator.co

_delirium pointed out the regulation that allows Sprinter and San Diego Trolley to get around the weight requirement in this comment: http://news.ycombinator.com/item?id=3060835 http://news.ycombinator.com/item?id=3060835 In doing some more research, Utah's FrontRunner has a completely disconnected network that allows them to get around the weight requirement. Apparently they went with standard US commuter equipment (MPI locomotives and Bombardier coaches) because of grade crossings and collision concerns. No sense in having a super-light train at high speed with grade crossing that carry many trucks.