How to enforce a Low Emission Zone


Trevor Ellis served as Enforcement Infrastructure Project Manager on the original London Low Emission Zone and recently chaired the ITS UK Enforcement Interest Group. He also runs his own UK-based ITS consultancy. Traffic Technology International caught up with Trevor to talk ALPR, LEZs, road-charging and much more …

Why are air quality and emissions reduction becoming so important to cities such as London?

The most recent figure on the number of deaths caused by poor air quality was 29,000 per year in the UK. There’s a lot of publicity around road safety, but we have about 1,700 deaths caused by road accidents per year. If those two figures are correct, then the concentration on road safety over air quality makes no sense – we should be putting all our efforts into air quality because it’s an order of magnitude higher.

The road casualty figures have come down dramatically because of a concentration on road safety and a lot of people are alive today who wouldn’t be alive otherwise. Road casualty figures are easier to define because if someone dies in an accident there’s no doubt about it, but with people who die from lung disease the cause is less visible. London’s air quality is very much worse than EU standards, so they have to do something about it and the Mayor, Sadiq Khan, has taken it up in a way the previous Mayor probably didn’t. Other UK cities are likely to have to follow London’s lead.

How does the London Low Emission Zone (LEZ) differ from the London Congestion Charge?

The London LEZ uses much the same technology that is involved in enforcing the London Congestion Charge and it was actually procured under an extension to the contract that was originally in place for the Western Extension to the London Congestion Charge. The original London Congestion Charge was set up in 2003 and in 2008 the London LEZ went live. The LEZ covers more or less all of Greater London inside the M25 whereas the Congestion Charge covers a very much smaller area in Central London.

Is the Congestion Charge essentially a profit-making exercise – and, if so, how does the LEZ differ in purpose?

When the LEZ was introduced it applied to heavy vehicles only and if your vehicle was of a lower Euro emissions standard, then either you had it fitted with a particulate filter and certified at an approved test station – or else you had to pay a very high charge of about £100 a day. The aim of the Congestion Charge when it was first introduced was demand management – to reduce traffic on London’s roads – although as a by-product of that it does, of course, make revenue for Transport for London (TfL). The aim of the LEZ was not to bring in money but to stop the most polluting vehicles from coming into London. It was deliberately done so that you didn’t have to make many trips into London before it became worthwhile for you to actually have a particulate filter installed.

With the London LEZ covering such a large area, it must be impractical to install ALPR at every entry point. Is there an inverse correlation between the size of a LEZ and the effectiveness of ALPR as an enforcement tool?

It’s more expensive, sure, but you need to think about the objective and the difference between a road user charging scheme and an LEZ. With an LEZ you are trying to get people to use the right vehicles rather than charging them every day for the use of vehicles. You don’t necessarily catch them every day as you may do in a road user charge situation, but you try and get a behavioural shift, rather than a revenue.

Some LEZs in mainland Europe do not have automatic enforcement but just rely on manual checks. You’ve really got to think about getting compliance. If it’s unenforced and people do violate it, you’re still probably better off having it than not. The ideal situation is that you have no violations at all, so you get no penalty income but you’ve achieved your objective of improving the air quality.

How has ALPR software and technology improved since the London LEZ was first set up in 2008?

There have been general improvements in camera technology; even the camera in your smartphone now has mega-pixels. The original cameras on the older ALPR systems were analog types and didn’t have as much resolution, which made the ALPR process less accurate. Also, the processing power is much greater now and much cheaper, so you can do a lot more, particularly with optical character recognition – the part that actually reads license plates from the image and creates the license plate output.

Those are the technological advances and I don’t think there have been step changes, they’ve been incremental changes over the years. In the early days, the London Congestion Charge got a lot of bad publicity because they were giving out penalty charge notices to people who’d never been to London; I think the classic case was when they gave a penalty charge notice out to a vehicle that was in the Beaulieu Motor Museum, which the newspapers loved. But they did a huge amount of work on the back-office processing in terms of recognizing the shortcomings of ALPR systems and making sure that you have systems and processes that catch the incorrectly-read ones so you can manually view them and correct them before they go out of the door.

In its early days, the Stockholm Congestion Tax ALPR generated a lot of false positives based on Estonian and Latvian plates with a similar format to Swedish ones entering the charge zone. Are problems of that kind commonplace?

It’s the syntax – the pattern of letters and numbers – which is the same. There are a number of crossover countries like that and it’s a numbers game: it depends what percentage of your vehicles come from those foreign countries that have potentially ambiguous plates. There are ways that the ALPR system can usually pick up or distinguish them. Some have little dashes between the characters or sometimes you can look at the font or character spacing to try and make the decision on nationality.

Do DSRC tags or the sticker systems used in some European cities provide viable alternatives to ALPR in terms of LEZ enforcement?

DSRC is mainly used in tolling systems and in general it’s more reliable than ALPR. But a tag implies that somebody’s co-operated with you and of course people who are trying to evade either a charge or a LEZ are not going to be nice and put a little tag up there so that you can identify that they’re non-compliant– so you have to have the ALPR system there to identify the non-compliers.

A sticker system is obviously prone to all sorts of fraud so authorities are trying to go away from them to easier systems with a database rather than a sticker. Stickers have to be enforced by traffic wardens or police, who in general are not very happy to take on enforcing things like that. They’ve tried to get away from things like bus lane enforcement, for example, because their performance indicators are all around crime reduction and safety. Certainly, in the UK the police are short of resources and so they try to concentrate on things the public want the police to do – and I’m not sure that enforcing LEZs would be very high on that list.

You draw a very clear distinction between LEZs and congestion charging in terms of their purposes. But doesn’t charging have the advantage of paying for itself while reducing traffic by 20% and hence yielding significant improvements to air quality?

It does have that effect; it’s demand management and there are not that many tools for demand management open to the authorities. Road-user charging is one of them and is probably the least used because it’s a political hot potato. The public feel they’ve paid for the roads through road and fuel tax and they don’t want to pay again.

All governments are facing revenue issues with their fuel tax take declining year-on-year because of cars getting more efficient and because of electric vehicles which pay no fuel duty at all. It’s worldwide and some people believe that road-user charging is inevitable. The funding situation needs to get a lot worse before it will overcome the political obstacles, but if there’s a large-scale switch to electric vehicles it gives the government a huge revenue problem.

Click here to read our full LEZ feature from Traffic Technology International April/May 2017.

June 7, 2017

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About Author


Tom has edited Traffic Technology International (TTi) magazine and its Traffic Technology Today website since May 2014. During his time at the title, he has interviewed some of the top transportation chiefs at public agencies around the world as well as CEOs of leading multinationals and ground-breaking start-ups. Tom's earlier career saw him working on some the UK's leading consumer magazine titles. He has a law degree from the London School of Economics (LSE).