Pedestrianisation of Oxford Street seems to be inching up the agenda. One of the big political objections is that buses are the only disabled-accessible public transport to that area but once Crossrail is operational that will no longer be true.

The buses still have to go somewhere though - the huge number of routes along Oxford Street is not about serving Oxford Street per se so much as about getting them across town. Honestly I'd be surprised if buses were the big source of pollution though - the fleet is quite modern and many of them are hybrids that deliberately run electric-only through the most polluted areas.