A railway system that uses hydrogen fuel cell technology; a train powered by hydrogen fuel cells. —adj.
Hydrogen trains, or hydrail, are not subject to many of the barriers preventing the mass adoption of fuel cell transportation, and their deployment could provide a transportation infrastructure around which additional hydrogen and fuel cell applications may be built. The first hydrogen-powered train models are currently being demonstrated in Japan and Europe.
—"Appalachian State University co-hosts International Hydrail Conference in Spain," US States News, April 14, 2008
And then there are trains, or "hydrails," as some call them.
"Hydrogen fuel cells as an application for passenger trains is very real," says Mike Hardt, vice-president of North American services for Bombardier.
In fact, Ontario may have some catching up to do if it's serious about being a world leader in hydrails. A European consortium called The Hydrogen Train concluded a study last year that looked at what it would take to demonstrate a hydrogen train in Denmark by 2010.
—Tyler Hamilton, "All aboard the GO hydrogen express," The Toronto Star, October 21, 2007
—Stan Thompson, "The Mooresville Hydrail Initiative," International Journal of Hydrogen Energy, February 17, 2004
You probably err in believing some people use "hydrail" as a noun. I've attended hydrail conferences and made invited presentation in eight countries involving some fifteen nationalities and I've never heard "hydrail" used as a noun or qualified by a definite or indefinite article (a, an or the).
As you say above, I coined the word. It's an adjective, e.g., a hydrail locomotive.
Hydrail trams, however, are "hydrolleys" and "a hydrolley" or "the hydrolley" are good usage.
Thanks for the feedback. However, it's quite clear that "hydrail" is being used as a noun in the two example citations. I believe you coined the word as an adjective, but people are definitely using it as a noun (as a simple Google search for "hydrails" will attest). Word Spy takes a descriptive (as opposed to prescriptive) approach to neologisms. Note, however, that I've added the adjectival sense to the definition.