According to EcoVelocity, CO2 in London could be reduced by 4,000 tons a week if all of the metropolitan area's black cabs were electric. EcoVelocity calculated the figure based on the CO2 emissions of London's 22,000 registered Hackney carriages (black cabs), but says the figure would more than triple if all the other of London's private-for-hire vehicles went electric too. The study took into account the CO2 emissions of the three most common Hackney carriages on London's roads – the TXI, TX II and TX4 built by Manganese Bronze – as well as the average daily mileage of cabbies.
Since road transport is responsible for approximately 80 percent of the airborne pollution in Central London, where air quality is at its worst, and black cabs account for around 20 percent of that pollution, electrifying the taxis would, by EcoVelocity's calculations, cut the city's pollution by one-fifth. The latest black cab, the TX4, meets only the now-outdated Euro 4 standards.