Having driven along London Wall at 1mph in thick diesel fumes, I think this is a good thing, but in London it tends to simply push most of the through traffic onto ever more crowded corridors such as the A4o past Euston Station (for the current congestion charge) and the South Circular (for the future ULEZ).
Bear in mind that Motability cars won’t be affected so the roads may just get clearer for us.