Instead of desperately trying to reduce road congestion in the short term, politicians should be using traffic as a tool for making urban transport more sustainable, writes Phineas Harper.

New research claims London's roads are the most congested in the world. But rather than wasting money and emissions building new roads in self-defeating attempts to reduce the time that Londoners who drive spend in traffic jams, politicians should be doing the exact opposite. Managed strategically, congestion is critical in supporting the transition to safe, sustainable transport.

Car horns, as every wannabe driver learns (then instantly forgets), can only be legally used in the UK "to warn other road users". "Never sound your horn aggressively" declares the British Highway Code, yet the bleating of horns punched by frustrated drivers venting fury at learners hesitating, cyclists existing, or some other minor inconvenience is a frequent feature in the soundtrack of city life.

Managed strategically, congestion is critical in supporting the transition to safe, sustainable transport

New census data has revealed that just 20 per cent of Londoners commute by car and 41 per cent of London households have no car at all. Yet despite this relatively low level of car ownership, the city is disproportionately designed to incentivise driving. At nearly 20,000 hectares, 12.4 per cent of land in the capital is taken up by roads – significantly more than the just 8.8 per cent of London currently used for housing.

For some boroughs the imbalance is even more extreme. In Tower Hamlets, for example, though 66 per cent of households don't own a car or van, an enormous 17.1 per cent of land is used for roads while only 7.5 per cent is reserved for housing. This dramatic over-provision of road space means that though many Londoners don't drive, the ones who do push the average number of car or van trips per person per year up to 240. London is addicted to cars.

One symptom of this addiction is Jill, a 1,800-tonne tunnelling machine currently burrowing under the Thames. Nicknamed after the first female London bus driver, Jill the drill is scooping out 600,000 tonnes of earth from below the riverbed to make way for a new underground dual carriageway – the Silvertown Tunnel. Inaccessible to walkers and cyclists, and opposed by both the boroughs it will connect, the tunnel will cost more than a billion pounds and lead to a dramatic increase in East End traffic.

Despite its backers' claims that the new tunnel will eliminate "chronic congestion", it is likely to have the obverse effect. Locals, who might otherwise have taken sustainable transport, will be encouraged to drive by the massive new stretch of tarmac. Significantly more cars and HGVs will be drawn to the neighbourhood, creating bottlenecks on both sides of the river.

No amount of new roads will ever eliminate congestion

No amount of new roads will ever eliminate congestion because the more roads get built, the more people drive. This truism of traffic management is called "induced demand" and has, as professor Petter Naess observes in the European Journal of Transport and Infrastructure Research, "been understood theoretically for at least one-and-a-half centuries and demonstrated empirically in several studies over the latest eight decades".

Most obvious in places like Los Angeles, where even colossal 12-lane freeways are regularly clogged as traffic simply increases every time the city adds a lane, induced demand affects London too. In the run up to the 2012 Olympic Games, for example, billions of pounds were spent widening the M25 orbital motorway in the hope of reducing its notorious congestion.

However, a 2021 study led by the former chief scientist of the UK Department for Transport David Metz found that the additional lane had delivered no long-term increase in the speed of travel. Instead, the wider road simply encouraged more Londoners to drive, leading to a 23 per cent increase in traffic, predominantly comprised of locals making short trips.

Cutting car use is not just about reducing exhaust fumes. Electric cars may produce less local pollution than petrol ones but still require enormous quantities of energy and carbon emissions to make and run. They rely on rare metals such as lithium, which the International Energy Agency is already predicting will be in short supply by 2025.

Moreover, car-based urbanism, electric or not, is inherently unsustainable, creating low-density, inefficient and dangerous cities. A grieving parent will find little comfort in learning their child was run over by a Tesla Cybertruck rather than a diesel 4x4.

Ultimately, new roads like the Silvertown Tunnel are entirely antithetical to making the urgent transition to sustainable urbanism. Instead of increasing the amount of land supplied for roads in a self-defeating, short-term effort to relieve congestion, city planners should instead do the exact opposite – strategically removing land from the road network to decrease car use in the long term.

Car-based urbanism, electric or not, is inherently unsustainable

Though shrinking road space may initially appear to drive up congestion, Paris Metropolitan Region senior urban planner Paul Lecroart reports that research spanning 60 cities shows removing lanes from inner city highways quickly reduces traffic by 14 per cent without "deterioration in traffic conditions". Congestion, though impossible to alleviate by building new roads, can, if controlled strategically, be a powerful tool for reducing car use.

Some sustainable travel activists imagine that drivers can be coaxed into breaking their car addictions through investment in public transport and cycle alone. Their hope is that, as green transport options improve, more drivers will organically make the switch and car use and congestion will simply dwindle away without requiring politically-contentious alterations to the road network. Unfortunately this specious fantasy is critically flawed.

The knock-on implication of any fall in car use created by new sustainable transport options is that roads become clearer. But due to induced demand, quieter roads, just like new roads, simply encourage more people to drive again. In short, unless the overall provision of space for cars is reduced, sustainable transport initiatives make cars more seductive just as fast as they provide alternatives in a vicious circle.

To break this cycle, cities should not just build green transport systems but actively dismantle the old car infrastructure at the same time; narrowing roads, replacing car lanes with bus and bike routes, removing car parking spaces from streets, implementing Low Traffic Neighbourhoods, and continuously reducing the amount of land dedicated to cars wherever congestion is too low.

Such measures could be deployed in tandem with driving taxes like Singapore's Electronic Road Pricing, but toll-based solutions disproportionately impact the least well-off and can be easily repealed by future governments. Long-term physical reductions in the percentage of land reserved for cars, on the other hand, permanently reconfigure cities for sustainable transport.

A strategic reduction in road space means completely reframing the narrative around congestion. Congestion cannot be abated with ill-conceived new tunnels and bypasses, but it can play a key role in concert with effective sustainable transport systems in the fight against car addiction. Scrap the Silvertown Tunnel – and build bike lanes instead!

Phineas Harper is director of Open City and formerly deputy director of the Architecture Foundation. He is author of the Architecture Sketchbook (2015) and People's History of Woodcraft Folk (2016).

The photography is by Anouk Fotografeert via Unsplash.