Boris Johnson has long had a very relaxed attitude towards air pollution in London, which could prove both expensive and embarrassing, if London's lousy air quality attracts EU fines or causes action to be necessary at the 2012 Olympics.
The worst single type of vehicle for air pollution is the black cab. The cab is a London icon, but it's a vehicle that was designed in the last century when air pollution was less well-understood. Johnson has made a bad situation worse by cancelling the 6-monthly emissions check for black cabs.
However, he's now considering a new 'very low emission zone', which may apply to all vehicles, including black cabs. There wouldn't seem much point in it not applying to black cabs, given that they account for 35% of tailpipe emissions. But because the taxi fleet is rather old, many vehicles would need to be retrofitted with emissions control equipment to comply. According to London Taxi Drivers Association general secretary Bob Oddy "this would simply force cabs off the road." It won't, of course. Drivers of older cabs will need to get a newer vehicle or get the retrofit, but not many will be quitting their career.
However, if London is to 'green' its transport system, it does need fewer cabs. The fact is that the London taxi is the least 'green' transport mode. Each cab weighs around 2 tonnes, yet the typical load factor (number of passengers being carried) is around one passenger per cab. Consequently, emissions of all types (CO2, NOx, particulates) per passenger are an order of magnitude greater than other transport types except for private cars. In central London, black cabs account for around 70% of traffic. Because of the congestion they cause by their sheer numbers, and by their presence in bus lanes, they damage the efficiency of 'greener' types of surface transport (buses and cycles). Buses are slowed by congestion, which makes them less attractive and increases their emissions. Traffic levels, and the fact that there are virtually no low-traffic routes in central London, means many people are too scared to cycle. It's time the balance of priorities changed.