London has long been leading the charge to mitigate the negative effects of traffic in a city. It introduced its congestion charge in 2003.
This currently sees qualifying vehicles charged £11.50 to enter the congestion charge zone between 7am and 6pm, Monday to Friday.
Cars or vans (not exceeding 3.5 tonnes gross vehicle weight) which emit 75g/km or less of CO2 and meet the Euro 5 standard for air quality are exempt from paying the charge.
In 2013, transport officials announced that the scheme had resulted in a 10% reduction in traffic levels in its first decade. However, congestion charges alone do not necessarily reduce air pollution.
According to research presented in March at a meeting of the Royal Economic Society, the levels of three traditional pollutants – carbon monoxide (CO), particulate matter (PM10) and nitrous oxide (NO) – all fell in the four years following the introduction of the charge, with reductions as large as 25% to 30% for PM10 and NO.
However, the study found a sharp increase of between 10% and 20% in NO2 emissions in the same period. The authors argue that this increase is likely to reflect the shift towards diesel-based transport.
In October last year, London added the T-Charge (Toxicity Charge) to its congestion charge and this places an emission surcharge of £10 for the most polluting vehicles entering central London with the aim of phasing out older Euro 4 vehicles.
Transport for London, which runs the charging scheme, estimates that 40% of drivers subject to the emission surcharge will upgrade their vehicle and 7% will stop travelling into the zone.
“Introducing a congestion charge, modelled on London’s, should be a consideration for the most congested cities,” says Adeline Bailly, researcher at urban area think-tank Centre for Cities.
“Not only would such a charge help to cut down car use, it could also generate revenue to improve public transport, especially in less well connected parts of cities.”
London and Durham are the only places in the UK which operate congestion charging zones, although other cities, such as Bristol and Bath, are considering similar initiatives.
Plans launched by Bath and North Somerset Council earlier this month suggest a charge for high-emission vehicles driving into the centre.
Two of the suggested charging schemes would affect only coaches, buses, HGVs and taxis, while a third would also affect private cars with older engines which do not meet certain emissions standards.
Bob Goodman, cabinet member for development and neighbourhoods at Bath and North Somerset Council, says: “It may be possible for us to achieve the required air quality improvements without the need to charge cars, however, further detailed work has to be done before a final package is agreed later this year.”