Dieselisation
Weighing against the cost of, and inertia against, replacing the large investment that railroads had in existing steam power were the dramatic increases in flexibility and efficiency with diesel. The fastest and most powerful steam locomotives were faster and more powerful than diesels; however, their range of efficient operation was severely limited. Diesels pro-rate their fuel usage to the length of trains, which a steam engine cannot do. Multiple-unit diesel power is scalable to power requirements with one locomotive crew; steam power is not. A high speed Hudson steam locomotive is good for only one situation, high speeds on level grades. The diesel locomotive can be operated by a single person, with no need of a fireman to run the boiler (two person cab crews may be required for other reasons). Also, diesels use much less fuel and no manpower when idling, something locomotives often do. Diesels can be parked running for days unattended, whereas steam engines must be constantly tended to if not completely shut down. Bringing a steam engine boiler up to operating temperature is often regarded as both an art and science, requiring much training and experience. A diesel is much simpler to start and shut down.
Steam locomotive
In 2012, the Coalition for Sustainable Rail project was started in the US with the goal of creating a modern higher-speed steam locomotive, incorporating the improvements proposed by Livio Dante Porta and others, and using torrefied biomass as solid fuel. The fuel has been recently developed by the University of Minnesota in a collaboration between the university's Institute on the Environment (IonE) and Sustainable Rail International (SRI), an organisation set up to explore the use of steam traction in a modern railway setup. The group have received the last surviving (but non-running) ATSF 3460 class steam locomotive (No. 3463) via donation from its previous owner in Kansas, the Great Overland Station Museum. They hope to use it as a platform for developing "the world's cleanest, most powerful passenger locomotive", capable of speeds up to . Named "Project 130", it aims to break the world steam-train speed record set by LNER Class A4 4468 Mallard in the UK at . However, any demonstration of the project's claims is yet to be seen.