Daniel Firth, chief transportation strategy officer for Stockholm, Sweden, reveals some of the secrets behind his city’s successful, ALPR-enforced Congestion Tax.
How does the ALPR system that is used to enforce the Stockholm Congestion Tax work?
The Congestion Tax is a toll ring, basically. All vehicles driving in and out of the inner city of Stockholm pay a charge between 6:30am and 6:30pm, Monday to Friday, and the charge varies according to the time of day. There are about 25 charge-stations with cameras both forward-facing and rear-facing on every lane for entry and exit – that’s about 200 cameras in total. In Swedish law this is defined as a tax and the tolerance for failure rate we accept for a tax is much lower than the tolerance you would accept for a regular charge, so we wanted to be sure of getting a really high hit rate. [The Stockholm congestion tax is billed monthly to vehicle owners identified by the ALPR system]
And what is your hit rate?
The hit rate is somewhere over 99% as I understand it. There is also a system in Gothenburg and road charging systems on a couple of newer bridges in other parts of the country. The Swedish Transport AdministrationNational Highway Administration has a central office serving all these systems and that allows them to keep costs down, rather than every city running its own system.
What was the cost of the ALPR system – and has it paid for itself in revenues?
The toll ring was introduced first as a trial in 2006 as part of a big political compromise and the cost was very much higher than if we'd done it today – about Skr250m (US$28m). But it paid for itself within four years and the money is going into a massive infrastructure investment that includes both new motorways and tube lines.
What are the advantages of using ALPR over DSRC transponders or a sticker system?
DSRC is no longer used because the charge is a tax and Swedish law says that the passive digital records you get from the DSRC are not sufficient for that. You need a picture in order to be able to withstand an appeal. If the legislation allowed us to just use a DSRC tag and have cameras at certain locations for enforcement purposes then there's potentially a cost saving, but because we need the cameras anyway, there's no point having the DSRC tags.
It's political but also traditional, I would say, and legislative. It's about the burden of evidence in cases and that’s the case for a lot of traffic enforcement. If you take speed fines as an example, in Sweden speed cameras are always facing the front of the vehicle because you have to have an image of the driver to be able to prove who was driving.
In the early days, what were the technical shortcomings of ALPR and how have they been overcome?
Our neighbors Estonia and Latvia based their registration [license plate] format on the Swedish one – three letters and three numbers. One of the issues was trying to make sure we didn’t get false positives where we’d send bills to a Swedish vehicle with the same number as an Estonian vehicle that had been through our zone. There are systems for flagging up plates that there are some question-marks around. Almost all the processing is done automatically, but there is the possibility of escalating certain images for people to take a look.
Every EU country apart from the UK must have an EU flag on the license plate with a letter combination for the country. The Estonian ones have 'EE' whereas the Swedish one is 'S' so, if you've got a good enough image, you can check to see whether it's an 'S' or an 'EE'. I haven't heard of any issues with this recently. There were a number of products available on the internet, like a plastic film you could put over your license plate that was supposed to obscure it or a plastic unit that would jut out over the top. None of them worked, but at the beginning there was a market for those things.
Before moving to Stockholm you worked for TfL. What are the main similarities and differences between the congestion charging systems in London and Stockholm?
They were both done to reduce the impacts of congestion. Coming here from London, it was hard to imagine that Stockholm had a congestion problem but the geography of the city means that it does actually have quite a serious problem at certain times of day. Despite the fact that the cities are very different and the the systems are designed quite differently, the results were more or less the same – a 15-20% reduction in traffic.
A lot of the differences are to do with the legislation. In the UK it's reasonably easy to get permission to put up cameras, but there’s much more security around getting access to data about who owns which vehicles, and to take a vehicle license plate and say this belongs to this person – but in Stockholm it's the complete opposite. It's what two different countries consider to be personal data and unacceptable surveillance. Legislation and culture, I think, are the two big differences.
In light of the new London 'T-Charge', might Swedish cities look to bring in differentiated charging for vehicles with more toxic emissions in future?
We from the city think that an additional charge based on emissions could be a really powerful tool to help us achieve our goals for air quality and climate impact reduction. We also think it is a more flexible alternative than a ban on more polluting vehicles which could lead to very high compliance costs for people who drive to Stockholm rarely. At the moment there is no legislation that would allow this, although there is an ongoing government consultation on a series of alternatives for stricter Low Emission Zones.
And would introducing such a charge present additional challenges in terms of using existing ALPR technology?
It’s a database question rather than a technology question. The easiest method would be to base a charge on something already available in vehicle registration, for example year or fuel type, but that isn’t necessarily the best or fairest way to achieve goals around air quality or CO₂ reduction. Were we to base it on anything else it would require a whole new registration method, which of course has an administration cost attached to it.
By Jack Roper
March 30, 2017
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