Almost universally accepted by business, and rarely challenged, is the received wisdom that rail transportation is greener than travel by road. But does this assertion still hold true?

This is no mere academic pursuit. Transportation is one of the fastest growing contributors to climate change, accounting for around a quarter of energy-related carbon dioxide emissions. Many experts foresee a five-fold increase in transport-related CO2 by 2030 in Asia alone.

In India, annual vehicle production has rocketed by 110% over the past six years. Production lines churned out 20.4m vehicles in 2012, compared to just 9.7m in 2006. In China, the world’s second largest economy, the vehicle population is set to soar to about 300m by 2030, from 65m in 2010.

In absolute terms, the picture is clear. Worldwide, road users account for about 71% of transport CO2 emissions, with railway companies making up less than 1.8%, next to 12.3% for aviation and 14.3% for shipping, according to the International Energy Agency and International Union of Railways.

Finding out whether road or rail is the most eco-friendly mode of travel is more difficult when trying to make a comparison passenger-for-passenger, however. There are so many factors for businesses to consider: from fuel type and speed to occupancy rate and load.

“If the train is going anyway, and you’re trying to decide which to use [road or rail], it obviously makes sense to take the train,” says Roger Kemp, former UK technical and safety director for Alstom Transport, manufacturer of TGV and Eurostar. “The additional energy consumption and emissions from you getting on are absolutely insignificant.”

But if the train is powered by diesel, with refined crude oil as its primary fuel source, and you have the option of using a hybrid electricity powered vehicle instead, then the equation may change, suggests Kemp, who has studied how, over some distances, many trains perform badly in comparison to cars.

“Diesel trains are frankly not that much different to cars. If you take a current car – say a small Citroën – which generates about 100 grams of CO2 per kilometre, that works out about 70 grams per passenger on average. It’s only when you get onto the electric trains, such as the Pendolino, which is down to 50 grams of CO2 per passenger, that cars just can’t compete.”

Despite being a former rail worker, Kemp is clearly not your typical railway enthusiast. “I’m very suspicious of some people in the environmental movement who take this ‘trains good, cars bad’ attitude. It’s an Animal Farm mentality of ‘four legs good, two legs bad’.” After all, electric trains are hardly green if powered from the grid by coal-fired plants.

Are car manufacturers streets ahead in green technology?

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.

It is no longer inconceivable that motor vehicles could one day rival electric trains, notes Kemp. “Because trains last a lot longer, those that were built in the last five years are still going to be with us for the next 20 years. Even if you introduced a super efficient train tomorrow it would be a lot of time before most trains would be using that type of technology.”

In India, one car manufacturer seeking to demonstrate the potential of new automobile technology is Mahindra Reva, based in Bangalore. In March this year it launched its new e20 electric car, a hatchback running on lithium-ion batteries.

The vehicle has a top speed of 80 kilometres an hour and a range of 100 kilometres per recharge which, when coupled with a solar power source, promises zero emissions.

With a price tag of around £9,800, the e20 remains unaffordable for most Indians. As far as Chetan Maini, Mahindra Reva’s chief executive, is concerned, however, the car nonetheless demonstrates how climate change pressures are encouraging the development of new innovations.

“For us, the advancement of battery technology leading to better range, higher speeds and also light weighting of vehicles will be the key,” he says.

Looking beyond the tailpipe

Technology is not the only factor undermining the standard argument made for rail travel. Recent studies by US researchers from the Universities of California and Arizona have found that too little attention is given to the auxiliary emissions generated by both rail and road infrastructure and supply chains.

Their argument goes that business needs to look beyond the tailpipe, so to speak, to the materials used in construction, lighting, salting and maintenance, as well as parking and even power for lighting and station escalators. Not factoring in these may give you the impression that rail is less carbon intensive than is in fact true.

“These activities have been accounted for in the past, but under different economic circumstances and they haven’t been attributed to transit,” says Mikhail Chester, assistant professor at Arizona State University. “The maintenance of infrastructure over the long run has significant environment impacts. It could even double the footprint of the mode.”

There are the other sustainability factors to consider: the greenfield sites bulldozed to make way for motorways and railway tracks and the respiratory and other ill health effects caused by pollution, not to mention social and economic impacts, such as traffic accidents.

Might rail be at risk of losing its claim to be greener than road travel? Not yet, asserts Chester, although the distance between the two may have narrowed. “As engine technology becomes more energy efficient and fuel become less carbon intensive, I think rail will maintain the edge,” he says.

“Cars are going to get greener in many different ways, through electrification and hybrid cars. But you also have advances in train technologies. We can’t forget that. Trains are not static, just like car innovation is not static.

“Even when you include, in addition to the tailpipe, the CO2 emissions from infrastructure, fuel production and the supply chain, on average rail will still have a lower carbon footprint than road travel, when comparing life-cycle to life-cycle.”

This content is brought to you by Guardian Professional. Become GSB member to get more stories like this direct to your inbox

Republicans in Congress who reject the science behind climate change could soon be reduced to political fossils, with new polling on Wednesday suggesting three-quarters of young voters find such views “ignorant, out of touch or crazy”.

The bipartisan poll conducted for the League of Conservation Voters found solid 80% support among under-35 voters for Barack Obama’s climate change plan – and majority support even among those who oppose the president.

On the flip side the poll found three-quarters of voters, or 73%, would oppose members of Congress who stood in the way of Obama’s climate action plan.

The findings could prove awkward for Republicans in Congress who have adopted climate contrarianism as a defining feature.

Some 55% of Republicans in the House of Representatives and 65% of those in the Senate reject the science behind climate change or oppose action on climate change, according to an analysis by the Centre for American Progress.

The house speaker, John Boehner, dismissed Obama’s plan to reduce carbon emissions as “absolutely crazy”. If the poll is right that would hurt Boehner even among members of his own party, with the poll finding 52% of young Republicans less inclined to support a candidate who opposed Obama on climate change.

The implications were even more harsh for those Republicans who block Obama on climate action and dispute the entire body of science behind climate change. “For voters under 35, denying climate change signals a much broader failure of values and leadership,” the polling memo said. Many young voters would write such candidates off completely, with 37% describing climate change deniers as “ignorant”, 29% as “out of touch” and 7% simply as “crazy”.

The climate cranks were unlikely to pick up many points with their base either; just under half of young Republicans said they would be less likely to vote for a climate change denier.

The poll, a joint effort by the Democratic firm Benenson Strategy Group and the Republican firm GS Strategy Group, could provide further evidence to a small group of moderate Republicans – mainly retired from politics – who have been trying to nudge the party to engage with the issue of climate change.

“As a Republican party strategist I believe that Republican candidates, Republican elected officials, need to find ways to demonstrate tolerance and understanding of what a young generation of voters need to see occurring,” said Greg Strimple of GS Strategy.

A few former Republican members of Congress – and an anonymous congressional aide – have publicly warned the party will lose voters, especially among the young, if it is seen as anti-science.

Obama, who has grown more high-profile about climate change in his second term, has played into those perceptions, calling out Republican climate cranks as “flat-earthers” in his climate speech last month.

At the moment there is no sign elected Republicans are eager for a climate makeover. At a Senate environment and public works hearing this week on climate change Republican Senators freely aired their personal doubts on established climate science and attacked Obama for failing to show “tolerance” to their alternative views.

In the house, meanwhile, Republicans were preparing bills to drastically reduce the powers and cut the budget by one-third of the Environmental Protection Agency – the main executor of Obama’s climate plan.

Outside Washington, however, Strimple said a rethink was under way. “I think there is a broad soul-searching going on with Republicans,” he said.

At Bugesera prison in Rwanda, prisoners do what prisoners usually do: eat, sleep, work, co-exist in a highly confined space. But the Bugesera inmates, leaders of Rwanda’s genocide, are also unlikely sustainable business pioneers. Their human waste is turned into energy that runs the prison.

“10 of our 13 correctional facilities now produce bio-gas from inmates’ human waste”, Rwanda’s deputy governor of prisons, Mary Gahonzayire explains. “Bugesera and another prison are run almost entirely on bio-gas. This is an opportunity that came up after the genocide, when the prisons got crowded. We thought, ‘why not use human waste for energy?’” The 10 prisons currently house 55,000 inmates. Now Rwanda’s government plans to expand human-waste energy to schools and hospitals.

Welcome to the new world of sustainable energy, where developing countries are taking the lead – by turning their sanitation problems into an asset. In India, bio-gas kits from companies such as Biotech India allow families to collect their human and animal waste and transform it into energy and cooking gas.

In China, a group called the Shaanxi Mothers has installed more than 1,300 bio-gas plants in Shaanxi Province. And in Accra, the US-Ghanaian company Waste Enterprisers has just inaugurated its first human-waste energy plant. “Human waste is an ideal source of energy”, explains Kartik Chandran, associate professor Department of Earth and Environmental Engineering at Columbia University. “It has the right constituents, and in the form we need them. And in many parts of the world it’s right there.” According to the United Nations, some 2.5 billion people around the world lack access to proper sanitation.

Making energy from human waste is, of course, far from a new idea. “In cities like Boston they’ve been doing it for years”, notes Jason Kass, director of Toilets for People, a sanitation advocacy group. “But it’s expensive and the plants are difficult to maintain.”

Grassroots projects, for their part, have been operating for several years. What’s changing now is efforts to move this clever combination of waste removal and sustainable energy beyond the Boston-or-grassroots level to a profitable business model. “We’d like to scale our project and make each unit cheaper”, explains managing director Dr A Saji Das of Biotech India. “Poor people can produce more than 50% of their energy needs from their waste. Here in India, more human-waste energy would also help solve the problem of deforestation.” 32,000 families and 47 municipalities currently use BioTech India’s bio-gas kit.

Jack Sim, founder and CEO of World Toilet Day, recently declared an official United Nations day adds: “Turning human waste into energy is a good solution even if it doesn’t make money, because it prevents disease. Treating diseases costs a lot of money.”

But researchers and companies know that human waste has to become more cost-effective. “Today the process is not optimised,” explains Chandran. “Bio-gas is very good, but there’s room to make it more efficient. And biodiesel, which is less common than bio-gas, currently sells at $7-8 per gallon. In order to be a competitive energy source, bio-gas needs a higher energy content, and we need to find a good way of converting bio-gas into liquid fuels.”

Waste Enterprisers, which collects fecal sludge from Accra and turns the solid waste into fuel, plans to open three more plants in Africa in the next three years and then expand faster. The best financial solution, argues CEO Ashley Murray, is to sell to factories: “Households could use it, but to generate volume you have to sell to large buyers. Plus, there’s the ick factor. People don’t like to cook with poo.”

With greater cost-efficiency, human-waste energy is poised to become a serious player. The main problem? The human body simply produces too little of it. Even if combined with animal waste, human waste doesn’t compare to the world’s oil resources. “I don’t think human-waste energy will ever be profitable”, says Kass. “Any efforts getting something useful out of human waste should be celebrated. But if Boston can’t make any money on it, how could developing countries?”

But, says Chandran, for countries with high education levels and substandard sanitation infrastructure, loo power is a huge opportunity: “China, India, South Africa, Brazil, even less developed countries in Europe could turn their sanitation disadvantage to a commercial advantage. Densely populated cities, especially if they’re a bit agrarian and have animal waste as well, could even generate this energy for export.”

These days, Rwanda’s prisons receive frequent visits from foreign government officials who want to replicate the energy generation at home. And for Mary Gahonzayire, the advantages of loo power are beyond doubt: “We save firewood, we save money, but most importantly, we save the environment!

This content is brought to you by Guardian Professional. Become GSB member to get more stories like this direct to your inbox