School pupils, Extinction Rebellion supporters and a long-standing local campaign group have joined forces against the tunnel, which would cross the River Thames in east London, near the Blackwall Tunnel. 

London Mayor Sadiq Khan seems determined to press ahead, although Hackney, Lewisham, Newham and Southwark local councils are against. Contracts are expected to be signed with a construction consortium in August.

The tunnel’s opponents say it would not only add to local air pollution, but also contribute to the further growth of car transport – at a time when the climate change danger means moving towards transport systems with fewer cars.

Downright untruths

The tunnel’s supporters have responded with misinformation and downright untruths. They have made shaky, unprovable claims that it will eliminate traffic congestion, improve air quality and ensure traffic volumes do not rise.

A senior councillor in Greenwich, which supports the project, has argued – against all the evidence – that the new tunnel will reduce greenhouse gas emissions.

Denise Scott-McDonald, the council’s cabinet member for sustainability, made the claim at last month’s meeting. In response to climate protests, the borough had declared a “climate emergency”, and green campaigners were insisting that that was incompatible with the Silvertown tunnel.

Here are five reasons why the Silvertown tunnel project cannot be reconciled with policies aimed at addressing the climate emergency. 

Air quality

1. Transport for London claims that, by easing congestion, the Silvertown tunnel would achieve an “improvement in air quality”. But research shows that this is very doubtful. 

Queuing vehicles pour out carbon monoxide, nitrous oxides, particulate matter and other toxins, as anyone who has been in a traffic jam knows. That is intolerable for people living nearby. But building more roads would be far more likely to spread the noxious mix differently than reduce the total quantity.

Transportation researchers at Portland State University in the USA crunched numbers for congestion-easing schemes, pollution levels, traffic levels and types of cars. They found that “congestion mitigation does not inevitably lead to reduced emissions”, but would more likely increase some emissions while reducing others. And getting traffic moving more smoothly increases the total amount of traffic … and can lead to higheremissions.  

City Observatory, an American urban planning think tank, called the link between congestion and carbon emissions an “urban myth”. They pointed out that, while traffic at 30-40 mph produces fewer emissions than traffic queues, cars moving above about 50 mph are less fuel-efficient and the volume of emissions per distance travelled rises.

Vehicle numbers

2. The main cause of rising greenhouse gas emissions from transport is the relentless rise in total vehicle numbers and total distances driven. This is a global problem of which the Silvertown tunnel problem is a small part.

The climate emergency means that any road-building project must be considered in the context of efforts to reduce the total number of vehicles and the total number of kilometres driven.

Transport accounts for about a quarter of greenhouse gas emissions from energy-related sources; cars account for about three-quarters of transport emissions. Most car journeys are in cities, and urban transport systems need to be refashioned to rely mainly on public transport, cycling and walking.

This means reversing long-standing trends. Car-based transport systems were introduced in the USA before the second world war, and have spread across the world since then. In 1950 there were about 55 million cars in the world, mostly in the USA; by about 2010, the number had passed 1 billion. And it’s not just the cars, it’s the highways, the parking spaces, and the way that built environments are arranged around them.

The reversal will have to start in rich countries: for every 100 people, roughly, the USA has more than 80 cars and the UK 58, compared to 17 in China and 2 in India. The spread of fuel-inefficient, gas guzzling cars – a rich-country trend pushed by car manufacturers in the three decades since global warming was discovered – will also have to be halted.

UK politicians, including the London Mayor, have acknowledged that there is a climate emergency. Turning back the expansion of car-based transport systems is one necessary response.

Road-building projects

3. Road infrastructure projects always result in more traffic and more greenhouse gas emissions. The Silvertown Tunnel will too.

Research of UK road-building projects have repeatedly shown that they produce more car journeys – so-called “induced traffic” – over nearly a century. 

A recent study of 80 road schemes, based on evaluations by Highways England, showed that they produced, on average, seven percent more traffic over three to seven years, and 47 percent more traffic over eight to 20 years. It also showed that economic benefits – such as those being claimed for the Silvertown tunnel – rarely materialised.

In the US, economists at the National Bureau of Economic Research concluded that building new roads does not relieve traffic congestion. They named the way that extra roads produce more, longer car journeys a “fundamental law”.

Many more studies have shown that road projects of all kinds help to increase the volume of traffic. That leads to calls for more road projects. 

This is why Greenwich councillor Scott-McDonald’s claim that the Silvertown tunnel would reduce emissions makes no sense. 

Vicious circle 

4. The Mayor and Transport for London have not dealt with the fact that the Silvertown tunnel would be part of this larger vicious circle of more cars and more roads.

TfL’s assessment of the tunnel’s carbon impact acknowledges that more than 150,000 tonnes of carbon would be emitted during construction. But it claims a very low figure for future emissions from vehicles as a result of construction (0.4 percent higher). 

That number has been produced by modelling scenarios. And those are based on a key assumption that overall traffic volumes will be kept down by road tolling. A spokesman for TfL told me that the modelling “demonstrates that overall traffic does not increase as a result of the Silvertown tunnel scheme”, and that “in a high [traffic] growth scenario a higher user charge is applied to manage traffic demand”.

But these claims do not stand up. Road charging might penalise local residents but fail to reduce future traffic flows. A future Mayor might change, or abolish, the charges. 

And, most important of all, decades of research on earlier road projects shows that they are part of a vicious circle. In the end, they always produce more traffic. And that produces more roads. Betting that this one will be different – instead of investing in non-car transport schemes – is playing games with the climate crisis.

Social trends

5. To address climate change effectively, transport policies must focus on reducing the total number of cars, and the total distances driven. This means a sea-change in economic and social trends: dumping road infrastructure projects is just the start.

The point of cancelling the Silvertown Tunnel project is not to leave everything else as it is. It should be scrapped as part of a transport policy for London that reverses for good the inexorable rise of roads and cars.

In place of the piecemeal measures in the Mayor’s Environmental Strategy, an integrated approach is needed that prioritises cheap or free public transport, cycling and walking.

Near-zero-carbon and zero-carbon transport technologies are needed, together with post-fossil-fuel energy systems. The rush hour needs to be made a thing of the past by new ways of working and living. 

Without such a bold approach, the climate emergency is being reduced to empty words.

This Author 

Simon Pirani is author of Burning Up: a global history of fossil fuel consumption, and a Greenwich borough resident.

Image: Ross Lydall, Twitter.