This site uses cookies. By continuing to use this site you agree to our use of cookies. To find out more, see our Privacy and Cookies policy.
Skip to the content

[IOP] A community website from IOP Publishing

environmentalresearchweb blog

Greening road transport

By Dave Elliott

Road transport is responsible for around 15% of global carbon emissions. Can this be cut? The first question to ask is – do we want to have private and commercial vehicles on roads as at present? Buses, trams, trains, bikes and walking may be better for many journeys. But assuming we still need private and commercial road vehicles for at least some purposes, the most direct and least disruptive way to reduce greenhouse gas emissions is to switch to lower carbon fuels, biofuels and synfuels. That’s easier than switching to electric vehicles (EVs). However, there are limits to biofuels – EVs are likely to win out.

Even if the rate of use of biofuels is matched by the rate of replanting, there are still net carbon debts and eco-impacts. It takes energy to harvest and process the crops, CO2 remains in the atmosphere while the new plants grow, biodiversity may be undermined and there can be land-use conflicts with food growing. And with some low-yield biofuel crops, the net energy gains can be marginal or even negative. More productive advanced biofuel crops may improve on that, but they are still not carbon-free, and it seems unlikely that we could grow enough biofuels to replace significant amounts of petrol and diesel use without having major eco-impacts. Biogas produced from wastes is less of a problem, but the volumes likely to be available are limited – and it’s maybe better used for heating.

Synthetic fuels of various kinds may be a better bet, but so far the costs are high. For example, it is possible to use electricity from wind or PV solar systems to electrolyse water to make hydrogen gas, for use either via combustion directly in car engines (or gas turbines) or in a fuel cell, to make electricity for an electric motor drive. It can also be converted into liquified synthetic methane (CH4), using CO2 captured from the air or from power station exhausts. That, like biogas, could be good for trucks and vans.  Some also look to synthetic methanol made from methane, or even ammonia, as a new carbon molecule-free fuel.  But both are toxic…

Unfortunately, these multiple conversion steps also each involve energy losses. If you have cheap electricity to start with, that may not matter too much (and if it’s surplus wind or PV power, then it is in effect free), but even so, why not use it direct in a battery electric car? The conversion losses are then very low. Certainly electric vehicles seem to be winning against hydrogen cars so far. Delivering electricity to car batteries is more straightforward than delivering liquid hydrogen to an on-board cryogenic tank. Although batteries are heavy and limit the car’s range, they are getting better and cheaper.

So for the moment most of the emphasis is on electric vehicles – and on stimulating uptake. They may cost less to run than conventional cars, but there are problems: the battery pack adds to the cost and has to be replaced regularly. They also need charging!  EV owners can charge them at home, which may be fine for short commuting/shopping trips, but for longer distance trips the UK is trying to get more public charging points established around the country. Ecotricity has already installed some at motorway services and there are some provided, for example, by local councils at other sites, in all around 11,000. The UK Department for Transport recently proposed plans to set common standards for all public charge points: at present there is a variety of plug-in socket formats.  But it’s also supporting hydrogen refuelling infrastructure.

Transport Secretary Chris Grayling said: ‘Our ambition is for nearly all new cars and vans to be zero emission by 2040.’ And subsequently, with urban air pollution worries growing, the new Environment Secretary Michael Gove has said the policy will be to halt all new petrol and diesel car sales by 2040. There is a way to go on that. Better batteries and charging infrastructure are clearly key, as are scrappage schemes for older cars. But the government already has a £4m programme to help businesses to switch their large trucks and vans to electric models through the Plug-In Van grant, as well as other grants and incentives for EV purchase. As a result, the number of new registered ultra-low emission vehicles (ULEVs) has risen by 250% in just two years, with more than £600m pledged so far over this Parliament to boost the market. The UK has the EU’s second highest level of EV sales.

However, it’s still pretty marginal, as is the uptake of biofuels. The UK had agreed with an EU plan to increase the proportion of biofuel included in fuel mixes sold but that has proved hard and caps have been set by the EU in response to concerns about eco-impacts. At present, liquid biofuel contributes around 3% of the fuel used in UK road transport. Sustainable sourcing has been an issue. Initially most biofuels were imported but REA says that UK biodiesel is now largely made from waste feedstocks, in particular used cooking oil’, with no palm oil now being imported, and UK feedstocks for bioethanol have risen, so overall 26% of biofuels are now UK-sourced, up from 8% in 2008.

The situation in the US is a bit different. Biofuels, bioethanol especially, prospered initially, driven by subsidy schemes aimed to help the beleaguered agricultural sector. Whether that helped much in net energy and emission terms is debated. So too is the impact of the more recent boom in electric vehicles (EVs). The US only gets around 15% of its electricity from renewables (as opposed to 25% and growing in the UK), so most of its EVs aren’t really very green. But the market for EVs is expanding. The Rocky Mountain Institute (RMI) says ‘During the last decade, the number of plug-in vehicle models available for sale has grown to more than 20, just as battery costs have decreased by 70%, and the number of EV charging stations across the US has climbed to more than 16,000’.

However, the RMI notes that ‘load growth from new EVs can pose challenges to the distribution system and to electricity customers—affecting grid reliability and increasing electricity costs’. That’s also clear in the UK – it could lead to a 20% extra peak power demand. But there are also some potential energy benefits. For example, as RMI notes, ‘technologies available today allow EVs to act as demand response resources and to assist with the integration of renewable energy onto the grid by managing when and where they charge’. Vehicle-to-grid (V2G) systems need careful planning – no one will like it if they find their car batteries drained when they want to go somewhere, or if the grid goes down if commuters all try to recharge their cars when they get home from work!  See the RMI’s report, Driving Integration: Regulatory responses to EV growth, for how these issue are being faced in the US.

So what’s the bottom line? Although public transport is by far the best environmentally, there are some green private road vehicle options and they are likely to expand. So we might hope to slow the rate of emissions in this sector. But it’s still pretty grim: road transport-related emissions in the EU grew by 17% between 1990 and 2014.

However, as noted above, the UK now has a 2040 phase-out plan. Norway and the Netherlands have similar plans, France too. And Germany is seeking a ban on the purchase of new petrol/diesel cars after 2030. But some say that unless these countries expand the renewables a lot more than is planned (or even possible), it may be hard for this to lead to reduced emissions. That may be overly pessimistic (see my next post), but it is clear that, given the limits on biomass, phasing fossil fuel use out of road transport fast, as well as from power and heat supply, will be challenging. If we also look at aircraft and shipping, it gets even more daunting.  IRENA only sees renewables supplying at most 15% of overall global transport energy by 2030. There is a way to go…as I will be looking at more in my next post on EVs and the grid.

This entry was posted in Renew your energy and tagged , , . Bookmark the permalink.
View all posts by this author 

Leave a comment

Your e-mail address will not be published.


  • Comments should be relevant to the article and not be used to promote your own work, products or services.
  • Please keep your comments brief (we recommend a maximum of 250 words).
  • We reserve the right to remove excessively long, inappropriate or offensive entries.

Show/hide formatting guidelines

Tag Description Example Output
<a> Hyperlink <a href="">google</a> google
<abbr> Abbreviation <abbr title="World Health Organisation" >WHO</abbr> WHO
<acronym> Acronym <acronym title="as soon as possible">ASAP</acronym> ASAP
<b> Bold <b>Some text</b> Some text
<blockquote> Quoted from another source <blockquote cite="">IOP</blockquote>
<cite> Cite <cite>Diagram 1</cite> Diagram 1
<del> Deleted text From this line<del datetime="2012-12-17"> this text was deleted</del> From this line this text was deleted
<em> Emphasized text In this line<em> this text was emphasised</em> In this line this text was emphasised
<i> Italic <i>Some text</i> Some text
<q> Quotation WWF goal is to build a future <q cite="">
where people live in harmony with nature and animals</q>
WWF goal is to build a future
where people live in harmony with nature and animals
<strike> Strike text <strike>Some text</strike> Some text
<strong> Stronger emphasis of text <strong>Some text</strong> Some text