Why can't London increase the Congestion Charge to the point where congestion is reduced to reasonable levels?
According to the Wiki article about the London Congestion Charge:
In 2013, ten years after its implementation in 2003, TfL reported that the congestion charging scheme resulted in a 10% reduction in traffic volumes from baseline conditions, and an overall reduction of 11% in vehicle kilometres in London between 2000 and 2012. Despite these gains, traffic speeds have also been getting progressively slower over the past decade, particularly in central London.
From the perspective of economics this doesn't make much sense - if London truly wants to eliminate traffic jams in downtown London, shouldn't they be slowly increasing the congestion fee until the task has been accomplished? Is this caused by political cowardliness or would it simply be inefficient to charge cars 50 pounds per day just to avoid traffic jams?
I am particularly looking for quotes from the government of London in regards to why the fee could not be increased.