My guess is that this is for the same reason as the fact that housing prices have gotten crazy high in London over the last decade: demand has continued to outpace supply (and in this case, the congestion charge). I mean, you can always suppress traffic if you're willing to raise the price high enough, right? It's just that politically, that can be a hard thing to do.
> the solution will have to be something like automated self driving cars integrated into a conveyor belt like system, which incentivise ride-sharing.
Sure, Minority Report-style traffic systems are probably a good idea in the long run (although that kind of thing is obviously a very long ways out). We'll still have to make investments in other, denser modes of transportation, though, as well as market-oriented policies like parking fees and congestion charges.