The Labour Party has criticised the cost of the new buses, accusing Boris Johnson of being "lavish" with taxpayers' money. They will cost £354,500 each.
Val Shawcross, the Labour transport spokesman on the London Assembly, said:
"There are plenty of green, environmentally clean, buses available on the mass-market now...the mistake that Boris has made here, is he's gone for a new tailored bus so he's paying way over the odds.
"He's probably paying over £100,000 more for each of these buses, so it's a very large waste of money.
"We could be getting the environmental benefit without paying this huge premium."
More top news
Official readings are recorded three metres in the air but a study found levels of nitrogen dioxide (NO2) were higher at pushchair level.
Tubes, trains, trams, buses, cable cars, river buses, taxis and going by foot - your guide to getting around during the strike.
Union officials rejected a revised offer from Underground managers during a meeting at the conciliation service ACAS this afternoon.