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Banning road building won’t save the planet
If you want to cut emissions from driving, focus on the fleet.
To understand why productivity growth has been flat in Britain for the past 15 years, try driving from St Neots to Cambridge at rush hour. According to Google Maps, travelling just under 20 miles east along the A428 can take as long as an hour and 15 minutes.
Why does such a short journey, in terms of distance, take so long? Blame a 9 mile stretch where the road narrows to a single carriageway. Traffic jams are a common occurrence and accidents can cause lengthy delays.
This is a problem because Cambridge has consistently added jobs at a faster rate than it has added new homes. House prices and rents in the city have surged to levels unaffordable for most and a majority of Cambridge’s workforce now lives outside the city. There are few surefire recipes for boosting growth, but allowing more people to access Cambridge’s uber-hot jobs market is surely one.
Yet the process of removing this bottleneck on growth has proceeded at a snail’s pace. As The Economist reported last year:
“In 2003 a regional transport study proposed upgrading the road to a dual carriageway. Eleven years later the transport secretary, Patrick McLoughlin, announced that the government would pay for it, as part of a road-building programme that would put “the motorist centre stage”. The years ticked by. Construction is now expected to begin next year, although that will depend on the outcome of a legal challenge. All being well, it will open in 2026.”
Why was the road challenged in the courts? It wasn’t a lack of consultation –local residents were consulted three times and the vast majority were in favour. Nor did the project threaten any endangered species –“the land is flattish and intensively cultivated.”
In fact, the Transport Action Network (TAN) took National Highways to court on climate grounds. TAN are an anti-car campaign, who argue that “building new roads increases traffic, leading to more carbon emissions.”
In Wales, legal challenges weren’t necessary. A new policy means roads can only go ahead if they meet uber-strict environmental criteria:
they must not increase carbon emissions,
they must not increase the number of cars on the road,
they must not lead to higher speeds and higher emissions,
and they must not negatively impact the environment.
The criteria are essentially impossible to meet. All major road building projects in Wales have been scrapped as a result.
The rest of the UK may follow suit soon. In its recent annual progress report, the Climate Change Committee recommended that all current and future road building be reviewed so they do “not lock in unsustainable levels of traffic growth”. The CCC wants new conditions developed so schemes are only “taken forward …if they meaningfully support cost-effective delivery of Net Zero and climate adaptation.”
Some Carbon Accounting
In the BBC’s coverage over the A47 Norfolk Upgrade challenge, they quoted a representative from Friends of the Earth.
“If we carry on with the government’s massive road building programme we don’t stand a hope of meeting our net zero or air pollution targets.
Is she right? In a word, no. Let’s look at the numbers.
The UK’s total greenhouse gas emissions were 407 million tonnes of carbon dioxide equivalent each year. Around 24% of that comes from transport and 91% (or 89 million tonnes CO2 equivalent) of that is down to cars. There are essentially two ways to reduce those emissions. You can either reduce the number of miles driven or you can reduce the net carbon intensity of each mile driven.
Anti-roadbuilding campaigners tend to focus on the former. Mixing tarmac may give off unpleasant fumes, but that’s not the only or main way a new road increases emissions. By making driving better (e.g. by increasing road speeds or reducing delays) new roads lead to more driving. And more driving means more emissions. The technical term for this is induced demand.
To calculate the carbon impact of a new road you need to add up the emissions from construction (and maintenance) and the emissions due to induced demand. Around 3,400t of carbon is released per 1 mile stretch of a 3-lane dual carriageway from construction alone. Most of that is from the energy used to produce the tarmac in the first place. Over a 40 year lifespan for a road, we are looking at annual emissions of 106t from construction and maintenance.
What about induced demand? An upper estimate from the academic literature on induced demand suggests elasticity of 1.03 for motorways near congested urban areas. In other words, if the total length of motorway lanes increased by 100%, the total number of miles travelled would increase by 103%. It should be noted that this upper estimate is high – the Department for Transport’s research found a much lower estimate of 0.2. Implying a doubling of the road network, would only lead to a 20% increase in the number of miles travelled. But, to prove a point we’ll stick with the upper estimate.
There are currently 247,800 miles of road in Great Britain. Of them, 31,900 miles are either motorways or A roads. And each year 170 billion miles are driven by motorists.
So if you add an extra mile of 3 lane dual carriageway, you can expect an additional 706,618 miles to be driven each year. How many emissions does an extra mile travelled produce? It depends on what’s being driven.
At the moment, most (51%) cars are petrol, many (42%) are diesel and some (7%) are electric (including plug-in hybrids). On average, a petrol car releases 105g of carbon per mile and a diesel even more at 126g. While EVs release 55g - owing to the fact we still rely on gas to power (almost half of) our grid. So in 2023, an extra mile of road travelled will emit 111g of carbon on average.
Yet, each year more and more motorists trade their internal combustion engine (ICE) vehicles for EVs. Already, 17% of new cars sold are EVs and sales of new petrol and diesel will be banned after 2030.
And each year, our grid gets greener as more renewables (and hopefully SMRs) displace fossil fuels like gas and coal. By 2050, a mile driven by an EV will release just half a gram of CO2.
What all this means is an extra mile driven in 2030 will be less polluting than one driven in 2023 and an extra mile driven in 2050 will be less polluting than one in 2030. If you use the Government’s forecast for EV uptake from National Road Traffic projections, you’ll see the emission per vehicle mile fall from 111g in 2023 to 36g in 2050.
If we take all of this into account, one extra mile of road will add 3,233 tonnes of carbon emissions up to 2050, an average of 115 tonnes per year.
If you sum together all the extra miles added as part of Britain’s Road Investment Strategy 1 (all roadbuilding from 2015 to 2020), you get an extra 2,731,863 tonnes of emission up until 2050, an annual increase of 75,885. In other words, five years of road building would increase Britain’s annual emissions from transport by 0.1%. The Department for Transport’s own numbers for RIS1 suggest a slightly higher increase in emissions between 0.1-2% – but this modelling is pre-EV mandate and assumes a lower rate of EV take-up.
Let’s put that into perspective. The National Infrastructure Commission estimates that economic growth (between 2022 and 2035) alone will lead to a 10% to 28% increase in annual traffic volumes. More than 124 times the traffic volume increased from RIS1.
Or put differently, if the UK was able to speed up the EV roll-out by just a year, the average annual emissions from road transport would fall by 2%, which is 20 times the extra emissions from all road building between 2015 and 2020.
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How to decarbonise transport: focus on the fleet
To get to Net Zero by 2050, the Climate Change Committee reckon we need to cut emissions from roads to essentially zilch. At best, cancelling all new road projects will get us less than a 100th of the way there.
This should not be surprising. Even if Britain embarked on a massive road-building programme and started spending twice or three times much on roads as it currently does, new roads would still only be a small fraction of Britain’s existing 247,000 mile long road network.
What about the idea of cutting demand more generally? In the CCC’s Balanced Net Zero pathway, they estimate that 20% of the necessary emissions reductions will come from demand reduction. The rest comes from the shift to zero emission vehicles (ZEVs) - mostly EVs.
It may seem as if all of the ‘demand reduction’ emission savings are down to people cycling to work or getting the bus instead.
Yet, if you dig into that demand reduction number, as the Department for Transport’s Michael Dnes recently did in a Twitter thread, it turns out that number is more than meets the eye.
Part of the issue is the way they order their calculations.
“Some of the carbon savings within our pathways could be attributable to either behavioural or technological actions. In our analysis, we account for the impacts of demand reduction/behaviour change before considering any technological deployment.”
As Dnes puts it, “decide to leave your EV at home in 2050 and take the bus, and 100% of the carbon savings go to public transport.”
But of course, your bus trip didn’t actually prevent any carbon entering the atmosphere because if you made the trip by car, it’d have been with a zero-emission EV.
And looking into the methods further, he finds that half of the demand management savings aren’t actually from reducing travel. They’re from ‘eco-driving’ and as Dnes points out, that much of that eco-driving will be done by EVs (and other ZEVs).
When he breaks it all down, he finds that “91% of net zero comes from EVs, better conventional engines or smart driving. Another 7% is 'joint'. Only 2% comes purely from reducing car use or shifting mode.”
Put simply, if we want to cut emissions from roads and get to Net Zero then we need to focus on EVs. Making walking, cycling and public transport more attractive is worthwhile for many reasons, not least of all for reducing air pollution, but when it comes to carbon emissions, the focus must be on EVs.
How to cut emissions
There are all sorts of ways to reduce emissions, but they are not all equally cost-effective. Some carbon-intensive activities are extremely valuable and lack desirable alternatives. If your family lives on the other side of the world, cutting out air travel is a non-starter. By contrast, switching from expensive, dirty gas power to cleaner, cheaper alternatives like wind, solar, or nuclear is an easier choice.
In popular discourse, Net Zero often morphs into just zero. But, the point isn’t to stop all emissions - just enough to get to zero on net. And even then, there are different ways to reduce the same emissions. We could cut emissions from heating by turning our radiators down (making our lives worse) or we could switch to heat pumps powered by clean electricity (using technology better). What’s key is that we identify and adopt the methods that have the smallest impact on our standard of living.
Britain is a nation of motorists where most people get to work by car and that’s unlikely to change any time soon. When roads are congested, opportunities are limited. Not all congestion can be fixed with wider roads or new tunnels, but smart investments targeted at traffic pinch points can and do help.
A halt to road-building may reduce emissions, but it won’t reduce them by much. And it will come at a great cost – fewer Brits able to access good jobs. There’s a better way. Instead of forcing Brits out of their cars by making driving worse, let’s make driving cleaner by speeding up the rollout of better, cleaner, and, in time, cheaper electric vehicles.