Zero-emission vehicle
Spurred on by ever stricter regulations, technological advances have dramatically reduced the footprint of road vehicles in the past 20 years. In 1998, most new cars in the UK emitted an average of 186 grams of carbon dioxide per passenger kilometre. By 2020, cars will be required by the European Union to emit almost half of this: no more than 95 grams per vehicle. 
According Wikipedia, a zero-emissions vehicle, or ZEV, is a vehicle that emits no exhaust gas from the onboard source of power. Examples of zero emission vehicles include muscle-powered vehicles such as bicycles and electric bicycles. Battery electric vehicles and fuel cell vehicles powered by hydrogen are also included in thze panel.  
Concerning railways, since many years, tests have been carried out not to use diesel engines on trains, on the lines without electric catenary. So far, the results have been inconclusive.In 2017, Alstom produced a first prototype of a zero-emission self-propelled train. The Coradia iLint is the world’s only fuel cell passenger train, according to its French makers Alstom. Testing was carried out on the company’s own track in Salzgitter, Lower Saxony, with passenger test services runs set to begin at the start of 2018.   
According ‘The Verge ‘, the Coradia iLint may be the world’s first hydrogen-powered passenger train, but it’s certainly not the first vehicle to run on hydrogen fuel cells. Stan Thompson, former strategic planner at AT&T and long-term advocate of the use of hydrogen for rail transportation, coined the term "hydrail" in 2004 to describe any type of rail vehicle that uses hydrogen fuel cells. There have been prototypes and hybrid trains in the meantime, most notably in Japan.  
The Coradia iLint, based on the dmu Coradia Lint 54, is the new CO2-emission-free regional train powered by a hydrogen fuel cell, its only emission being steam and condensed water while operating with a low level of noise. Alstom is among the first railway manufacturers in the world to develop a passenger train based on such a technology. To make the deployment of the Coradia iLint as simple as possible for operators, Alstom offers a complete package, consisting of the train and maintenance, as well as also the whole hydrogen infrastructure out of one hand thanks to help from partners.  
Of course, you will say that the zero-emission railway vehicle is the électric train. This is true if we only calculate emissions from the vehicle alone. On the other hand, if one takes into account the manufacture of electricity or hydrogen, the zero emission vehicles does not yet exist. According to ‘Digital trends’, it is difficult to obtain hydrogen in a way that is both green and efficient. If hydrogen catches on as a "non-polluting" fuel, leaks from its production, storage and transport could worsen ozone depletion. Some experts estimate that around 10% of all hydrogen manufactured would leak into the atmosphere. Current losses are already greater than this. If all fossil-fuel usage were to be replaced, around 60millions tonnes of hydrogen would leak into the atmosphere every year - four times the current amount. Combined with natural sources, the increase would roughly double the total hydrogen input into the atmosphere.   
An other debate is concerned with electrical energy, within his production by a coal-fired power plant, gas power station or nuclear power plant.
At the moment, the zero-emissions vehicle therefore refers to the vehicle itself. And the electric train is well placed to take the 'lead' of the sector. 
The author:
Frédéric de Kemmeter 
Railway signalling systems. I'm a rail observer for over 30 years. How has the railway evolved over the decades? Which futur for railways? That's what I'm analyzing and explaining.

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Coradia iLint Dmu from Alstom which was presented at Innotrans Berlin in 2016 (photo Alstom)