The sustainability issue with transportation is not related to fuel. If you put automobiles on rails and let a computer drive them,you can go 10x faster on 10x less fuel with no accidents. The biggest benefit is that you no longer need to wait in line at a bus stop or train station. There are soooo many other things that you could be doing instead of driving, like talking on your cell phone. The energy savings are enormous with this system and would pay back construction costs in less than 5 years.