I know this has been posted elsewhere (notably by Eric Jaffe at Atlantic Cities).
Jonas Eliasson, Centre for Transport Studies at Sweden’s Royal Institute of Technology, describes what happened in Stockholm in this video published in late 2012. It is nearly 9 minutes long, so isn't taxing on your time.
I like his reference to the Soviet planner who rang an official in London in 1989 asking what official was responsible for managing London's bread supply. The answer being no one.
Perhaps some will take that analogy and wonder why the same can't be said for transport networks.
On Stockholm his key points are (much of this is already known):
- Congestion tax introduced as a trial in 2006, which ended in August 2006.
- Referendum passed the charge (by 53% of the vote of residents in Stockholm City municipality itself, not all of metropolitan Stockholm) in 2006.
- In August 2007 it was introduced permanently.
- In 2011, polling indicates 70% support for the charge.
- In 2011, traffic remains 20% below the levels seen before it was introduced.
- Surveys of motorists indicate they largely don't think they have changed behaviour, primarily because people slightly alter their behaviour most days, so there isn't the precise consistency of travelling that planners expect. It indicates that some travelled earlier or later (charges are lower or don't apply at different times), or changed mode or combined trips (reducing overall trips).
His key thesis is that measures like congestion charging can change behaviour by simply changing incentives, with dramatic results.
I'd also add that transparency about where the net revenues go (all have gone on transport projects, mostly major highway improvements in outer suburbs), has made a difference.
Moreover, acceptance is greater given that Stockholm has sustained improvements in travel times that demonstrate congestion has been reduced.
London has not seen such obvious improvements, in part because road space was reallocated to road users who do not pay the charge. Those benefiting have largely not been those paying.
That's not to say London's congestion charge is unpopular, but certainly anyone advocating expanding it or introducing new ones in the UK has the key problem that few believe that there is any noticeable difference in central London traffic between times when the charge is operational and when it is not.
It is key for public acceptability that congestion is noticeably reduced and the money collected is used to benefit those paying.