Stockholm congestion pricing has had long term effects on traffic levels

The European Commission DG Environment reports on a study that indicates that the congestion tax in Stockholm has managed to sustain and enhance benefits in congestion reduction over time.   The EC believes this has positive implications for the concept's application in other cities.

Stockholm congestion tax cordon map

The report says:

The results of this study suggest that congestion charging can work over the long-term, supporting plans to introduce such charges in other cities across Europe. The findings also demonstrate that some concerns about the charges, such as increased congestion on other routes, are not supported by the evidence, and that public acceptability may increase over time.

Non-exempt* traffic had reduced by 29% across the Stockholm cordon when the congestion charge was introduced in 2005, and that level of reduction has been sustained even though prices have not increased (so have reduced in real terms by around 2% per annum).  It appears that the charge has had a long term effect on changing driving patterns into central Stockholm.   However, researchers acknowledge that over time there will need to be real increases in prices.

Another criticism about congestion charging, that it increases traffic on roads adjacent to the charging zone, appears to have been without foundation, as there has been no significant increases in traffic or congestion on other routes, except that attributable to population increases.

Finally, public acceptability for the scheme is now 70%, up from 36% in 2006 (and a narrow majority in favour of the charge in a referendum), indicating that the benefits of permanent reductions in traffic volumes and improved mobility are now widely accepted.

In conclusion, the Stockholm scheme has not only worked, but sustained a step change in traffic patterns in the city and not distorted traffic movements outside the zone.  

It's worth noting that the Stockholm scheme is slightly more sophisticated than the London one, as it has higher charges at peaks compared to the interpeak period, and no longer has an exemption for so-called "green" vehicles, because the emphasis of the tax is to reduce congestion - and all cars contribute to that.  The other interesting dimension to the congestion tax is that most of the revenue is being used to support enhancements to roads outside the charging zone, which appears to be a key part of the charge gaining acceptance by people in Stockholm.

Finally, the official title of the charge is the "congestion tax" because under Swedish law, it is the only way the charge is enforceable.

* Exempt vehicles are only buses, emergency vehicles, motorcycles, diplomatic and foreign registered vehicles and those of holders of a disability parking permit.