What if... every city had a congestion charge?

Nowadays it seems you hardly have to wait five minutes for a bus in London. But if, like me, you grew up here you'll remember it wasn't always the case. In the 1990s, the average speed on the roads of London was slower than it had been at the beginning of the century, before the motorcar was invented.  All that changed in 2003 when the newly elected mayor, the 'right on' Ken Livingstone, brought in Europe's first urban congestion charge. The impact on traffic was immediate. But what did it do for carbon emissions? And should every other city in the world follow in London's footsteps?

There's been relatively little research into the emissions impact of urban congestion charging - primarily because surprisingly few such schemes exist. The world's first congestion charge was introduced in Singapore in 1975. Then came London. And even more recently, Stockholm introduced its own charging scheme. Other urban road toll schemes exist but these have been introduced primarily to raise income rather than cut traffic. And several cities, particularly in the developing world, run car free days where vehicles are banned in urban centres. In Jakarta drivers must leave their car at home once a week!

Residents walk on the roads during Jakarta's weekly car free days

Congestion charges can reduce emissions in two ways. The first is obvious. Less cars on the roads means less vehicles emitting CO₂. But in addition less cars means traffic moves faster with less stopping and starting. And steady driving is efficient driving.

Transport for London estimated that the congestion charge reduced the number of cars on London's streets by a colossal 27% between 2002 and 2003 after the charge was introduced. This corresponded to about 65,000 - 70,000 less journeys. Passenger surveys suggested about half of these journeys had been transferred to public transport, primarily buses (the charge was brought in to coincide with a multimillion pound investment in London's bus network). About 10% switched to other private transport like bikes and taxis. And a further 35% chose to travel around the congestion charge zone, or travel at different times of the day. What does this correspond to in emissions? ... Well, nobody seems to have estimated that. 

Unlike us, the Swedes - being the green nation they are - have estimated the carbon impact of their scheme. Their charge resulted in a 16% reduction in traffic over the city centre. And this corresponded to a 14% reduction in emissions.

£100 million was invested in London's buses before the congestion charge was brought in

So what would happen if every city in the world had a similar congestion charge? Let's do some back of the envelope calculations. Half the world's population live in cities so let's assume half the world's billion cars are in cities too (I'm sure this isn't right - but I searched high and low for an estimate to no avail. If you know better - put it in the comments below). The IPCC says 13% of the world's carbon emissions come from transport and (rather lackadaisically) says 'about three quarters' of that is from road vehicles. So, do the number crunching and you'll find that, if every city introduced a congestion charge with the same impact as Stockholm's, global carbon emissions would be cut by about 0.1%.

It might not sound like a huge amount but there's loads of other benefits to a congestion charge. It takes less time to get about (vehicle speeds in London have increased 17% from pre-charging levels). And positive impacts on health have been reported in both London and Stockholm due to the decrease in atmospheric concentrations of airborne pollutants and nitrogen oxides. A King's College study estimated the congestion charge gave an additional 183 years of life per 100,000 of the population within the charging zone. Even the economy, ever the victim of emissions reduction schemes, doesn't seem to have suffered. A report by John Lewis found that, although takings had reduced at their central London stores, there was no measurable effect on central London retail overall. With stats like these, rolling out congestion charging to every city in the world seems like a no brainer!