The Europeans have mandated much more expensive effectively zero sulfur and ultra-low aromatic (particulate) Diesel 3 or Diesel 4- The equipment that this runs- DMU's- are very light vehicles for light branchline services. Siemens car here does not meet this, as yet. Some hybrid technologies come close, but are not applicable to high speed operations, as yet.

Some newer American diesel engines (engines not locomotive engines) can meet more stringent requirements with this cleaner fuel. Costs for this cleaner diesel fuel would be significantly higher, but it may be mandated here, to meet our increasing emission health particulate standards for heavy duty trucks.

Right now, nothing in Europe or the World market, that I know of, meets the SMART criteria for both emissioins and performance, with a diesel prime mover. It is being worked on, and I expect some advances. But, is not something that I would recommend a small agency, on a tight budget and schedule, should tie itself too, until it is commercially achieved. They do not control the variables in technology, regulation, markets, or compliance and will pay an enormous premium to try to acheive this standard on their own. It is a laudable goal, but not necessarily a very realistic decision.