As the growing global pattern towards urbanisation and the centralisation of jobs continues, conditions increasingly favour rail travel.
With the worldwide market predicted to enjoy 2.4% steady annual growth until 2020, according to a joint UNIFE / Boston Consulting Group study, along with consultants SCI Verkehr suggesting demand for rail equipment will top €160bn globally by 2015, the quest is on to find the optimal approach to modern mass transport needs, putting railcar choices in the spotlight.
The sector can be a challenging one for new technologies. As Roger Cobbe, Policy Director for Arriva Trains and the UK's representative on the Community of European Railways Management Committee says: "Railways are expensive things, and what you buy is largely guided by what is already there."
Given cost constraints, radical innovation clearly has to offer very real advantages - and some would suggest the new generation of genset locomotives, and ultimately the emerging hybrid designs, do just that. If so, are they about to mount a serious challenge to the long-established electric / diesel-electric paradigm?
A growing global presence
According to a recent report from Pike Research, both hybrid and genset railcars will develop an increasingly large presence on the world's rail markets between 2015 and 2020, with the sales of hybrids forecast to rise at a compound annual growth rate (CAGR) approaching 25%, representing some 100 to 170 units being purchased each year.
Pike's senior analyst, Dave Hurst, points to changes in diesel emission regulations, due to come into effect within the EU and North America in 2014 and 2015 respectively, as potential drivers on the market, believing similar concerns in China and India - where rail infrastructure is growing rapidly - will up the demand for hybrids further.
Although genset units are initially expected to provide stiff competition as the market matures, with a predicted CAGR of 6.7% between 2010 and 2020, he believes that by the end of the decade, hybrid locomotives will be in the ascendancy, not least because of the strong return on investment they offer.
Nonetheless, there are some significant hurdles to be overcome along the way if railcars primarily driven by battery-stored power are to become a regular sight on the world's railways.
The electric challenge
"It's really all about electrification," says independent transport consultant Ernie Bell. "In parts of the world where it doesn't exist, or isn't going to for the foreseeable future, there's a good case to be made for these bi-mode railcars [hybrids]. But for much of Europe and Japan, where you already have electrification on 50 or 60% of the track, the argument is obviously much weaker."
The point is made even more directly by Cobbe. "You'll never introduce a hybrid train if you're already electrified."
For many in the industry, this sounds the clarion call for universal electrification, particularly as rail usage increases. "The greater the level of traffic, the more economic electric traction becomes. Since most main lines in Britain are reaching capacity along part or all of their length, they should all be electrified," says Piers Connor of PRC Rail Consulting.
However, as he points out: "For electrification or new high speed lines, the average planning to completion time for a new railway is 25 years." Evidently, the situation will not change overnight - something the UK's intercity express programme (IEP) was in part intended to address with its 'go-anywhere' provision, aimed at enabling trains to be able to travel the network without assuming that full electrification is necessarily imminent.
However, Mary Bonar of international law firm Stephenson Harwood and the Independent Transport Commission's rail expert, explains that the planned role of hybrids in achieving this has taken a knock. "The UK Department for Transport, having decided to procure hybrid trains, subsequently decided on more extensive but not total electrification of the network which arguably removed the main benefit of a specially designed hybrid intercity train."
Connor puts it more scathingly: "The idea of a mixed diesel / electric 'IEP' train as proposed by the present government is, quite frankly, daft. It is economically and operationally not fit for purpose. It is an answer looking for a question."
Fuel / weight paradox
While that may be true in the UK, elsewhere Bell believes hybrids may be an appropriate solution for heavily diesel-reliant rail systems - and not simply because of increasingly stringent emissions regulations. "There are many parts of the world which don't yet share our concerns over particulates and carbon. For them it's fuel consumption that they see as the principal benefit, and some of the demonstration projects that have been done in Japan and the EU have been turning in figures of 10 or 20% reductions. That adds up to a lot of potential savings over the year."
Batteries are, of course, key to achieving this. According to Hurst the projected sales of hybrids will call for around 514 megawatt hours (MWh) of battery capacity in the years leading up to 2020. Most of this, he predicts, will be provided by lead acid and advanced lead acid batteries - but that means a significant amount of weight at a time when the broader trend is towards lighter railcars.
Logically, this paradox between greater weight and improved fuel consumption should appear irreconcilable. However, it arguably provides the perfect example of a broader point independent rail expert William Barter makes about railcar selection in general.
"I think it depends very much on what type of service - rural, inter-urban, urban / metro - and what the needs are. There is a very strong case to be made that the way forward for railways is specialisation of assets for their respective markets."
There is one specialist role in particular for which hybrids appear ideally suited - one where the greater adhesion afforded by increased weight between track and wheel comes at a premium; shunting.
It is, then, no coincidence that Alstom's hybrid conversion of a 68 ton, former DB diesel-hydraulic shunter remains one of the most successful expositions of the technology to date, after the combination of a 200 kW Deutz diesel engine charging a NiCd battery virtually halved the locomotive's fuel consumption over a two-month trial.
Such successes aside, just how effective hybrids will ultimately prove in other roles over the coming years, competing against established systems of traction and against alternative emissions and efficiency technologies, remains to be seen.