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ULEZ is working: How London's Ultra Low Emission Zone is changing travel behaviours

Early results show the Ultra Low Emission Zone is successfully shifting passengers back onto public transport and improving London’s air, Nicole Badstuber reports

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London’s Ultra Low Emission Zone was introduced in April 2019
London’s Ultra Low Emission Zone was introduced in April 2019


In April this year, Mayor of London Sadiq Khan launched the world’s first Ultra Low Emissions Zone (ULEZ) in central London to tackle the capital’s poor air quality. Vehicles driving in central London must meet tight exhaust standards or pay a daily charge.


London’s air quality is poor – and dangerous. The city is struggling to meet air quality targets. In breach of the European Union’s legal limits and in excess of the World Health Organisation’s (WHO) recommended particulate matter levels, the aim of the ULEZ is to reduce nitrogen oxide (NOx) levels by 45%. Currently, roughly half of all NOx emissions come from road transport.


Since 8 April 2019, vehicles entering central London have to meet ULEZ exhaust emissions standards or pay a daily charge. This means non-compliant vehicles must pay both the congestion charge and the ULEZ charge to enter the central London congestion charging area.


ULEZ currently covers the same area as London’s congestion charging zone, but unlike the congestion charge, ULEZ operates 24 hours a day, every day of the year. It’s also set to expand to cover all of London within the capital’s major orbital arterial roads, the North and South Circular, in October 2021.


By all available metrics, ULEZ is a success – even more so than was forecast. On average, 77% of vehicles in central London now meet ULEZ exhaust standards – more than eight per cent points higher than the 69% forecast.


Fewer older, polluting, ULEZ non-compliant vehicles entered the charging zone in April in comparison to a month earlier in March before ULEZ – 9,400 fewer on an average day, representing a 25% drop.


By all available metrics, ULEZ is a success – even more so than was forecast


And vehicle number have continued to fall: the number of ULEZ non-compliant vehicles entering the zone fell by 38% in the six months since the introduction of ULEZ – with on average 13,500 fewer ULEZ non-compliant vehicles a day in July in comparison to March. Total vehicle numbers entering the central London charging zone also dropped and have continued to steadily fall each month since.


Data suggests that the ULEZ has not only discouraged driving polluting vehicles into central London but has encouraged the use of public transport instead, with Transport for London reporting higher than expected passenger revenue since the introduction of the charge.


ULEZ piggybacks on existing infrastructure and charging processes put in place in 2003 for the congestion charge: Automatic Number Plate Recognition (ANPR) cameras, installed at the entry points to the charging zone, record the number plates of all vehicles entering the zone. All busses operating in the central London charging zone meet ULEZ standards.


Residents living in or immediately adjacent to the ULEZ zone are exempt from the charge. This is a carryover from the congestion charge where the same residential exemption applies. However, this residential exemption will expire with the expansion of ULEZ in October 2021. Taxis and registered wheelchair-accessible private hire vehicles are also exempt from the ULEZ charge.


ULEZ is a cornerstone of the Mayor’s Air Quality Strategy and the wider London Environmental Strategy for the city. In addition to the legal requirements for air quality, improvements are also sought to improve public health and quality of life.


There is also an inequality dimension to pollution with vulnerable societal groups disproportionately affected by air quality, including children, older people and those suffering from chronic respiratory conditions. In 2015, a study by King’s College London estimated that London’s poor air quality is responsible for an estimated 9,500 premature deaths each year.


Not only has ULEZ discouraged driving into central London in polluting vehicles, it has also encouraged the use of public transport


ULEZ replaces the emissions-based Toxicity Charge (T-Charge) that was introduced on 23 October 2017. The £10 T-Charge applied to old, polluting vehicles – broadly speaking, that means diesel and petrol vehicles registered before 2006 – entering central London. The T-charge also operated on top of (and during the same operating hours) as London’s Congestion Charge (weekdays from 7am to 6pm).


In addition to ULEZ, London already has a city-wide Low Emission Zone (LEZ). It applies to heavy vehicles – lorries and buses – all day, every day. As with the ULEZ, those entering LEZ must meet emissions standards or pay a daily charge.


The effects of ULEZ were immediate and sustained. Vehicle compliance with ULEZ standards spiked upwards after introduction of the emission-based charge. In the first month of operation, 71% of vehicles entering the zone during the ‘work week’ complied with ULEZ emission limits – a 10-percentage point jump from 61% the previous month.


ULEZ’s performance has continued to improve, too, according to early available measures. The proportion of the traffic entering the zone made up of old, polluting, ULEZ non-compliant vehicles in the central London charging zone fell by nearly a third from March to July 2019.


By the summer, compliance rates (the proportion of vehicles compliant with ULEZ standards) had risen to 74% during the ‘work week’ and 77% per cent over the whole week (day and night) - ‘better than expected at this early stage’ according to TfL.



ULEZ is improving air quality in the capital, too. Nitrogen dioxide (NO2) emissions from road transport are down 31% - equivalent to 200 tonnes – in the central London charging zone according to preliminary estimates from Transport for London. NO2 concentrations along roadside locations are also down 29% – on average 24μg/m3 lower – compared to trend analysis modelling of a non-ULEZ scenario.


Particulate Matter 2.5 (PM2.5) emissions were 13% lower across the July to September 2019 – equivalent to five tonnes of saved PM2.5 compared to the non-ULEZ scenario. In addition, carbon dioxide emissions from road transport are 4% (or 9,800 tones) lower compared to non-ULEZ scenario modelling. As well as improving air quality, ULEZ has also reduced traffic volumes in central London. Traffic flows between May and September 2019 is from 3% to 9% lower year-on-year.


Comparing the proportion of compliant vehicles is the most accurate way to track changes in the vehicle fleet. Khan signalled his intention to tackle road transport-based emissions in February 2017, announcing that the T-Charge would come into force from October 2017. This announcement marked the start of political momentum to address air quality in the capital. Although the T-Charge did not take effect until October 2017, the announcement of the charge will have had an effect on individual and business vehicle choices.


The introduction of the T-Charge was just the start of an accelerated change in the vehicle fleet in London. To give an accurate review of the impact of the emissions-based charging policies we need to compare figures before the announcement of the T-Charge, as this was the first emissions-based pricing policy to be announced.


ULEZ is improving air quality in the capital. Nitrogen dioxide (NO2) emissions from road transport are down 31% - equivalent to 200 tonnes


In the two and half years since the announcement of the T-Charge, London has significantly cleaned up the vehicle fleet on its roads. There has been a nearly two-thirds (65%) reduction in the number of older, more polluting and ULEZ non-compliant vehicles in the central London charging zone between February 2017 and September 2019. This is equivalent to, on average, 40,200 fewer non-compliant vehicles a day. In the same time period, the percentage of ULEZ-compliant vehicles in the central London charging zone nearly doubled from 39% to 77%. since February 2017.


ULEZ’s higher than expected compliance rates have hit Transport for London’s (TfL) bottom line – potentially adding to their funding worries, although increased passenger income on the Tube and busses exceeds the loss.


Instead of the originally forecast £77m of revenue from ULEZ, TfL’s budget for the 2019/20 financial year is now expecting to take in only £55m. This is largely the direct result of a third fewer non-compliant vehicles entering London’s ULEZ. By comparison, net income from London’s congestion charge was £147m in the 2018/19 financial – £230m income minus £83m in tolling, enforcement and administrative costs.


Passenger income is up, however, particularly on the London Underground and on London’s busses. Transport for London has revised its passenger income budget up £29m for 2019/20. This more than makes up for the £22m of lost revenue on ULEZ. Higher ticket sales alongside ULEZ successfully deterring driving into central London suggests that ULEZ might be encouraging Londoners and visitors to opt for public transport over their car.


In October 2021, ULEZ will expand to cover all of London encircled by the North and South Circular, the city’s orbital arterial road network under a new scheme, ULEX. With the expansion, the residential exemption will expire. The residents who are responsible for 38% of the non-compliant vehicles entering central London every day will no longer be exempt from paying any charge, equivalent to 10,400 vehicles a day. Residents of the zone also enjoy the highest level of public transport access in the city.


The expansion is expected to reduce nitrogen oxide (NOx) pollution by a further 28% – removing 4,400 tonnes of NOx in Inner and Outer London by 2025. ULEX will cover an area encompassing 3.8m of the capital’s residents. ULEX forms a key part of the UK Government’s Plan for London to comply with air pollution limits by 2025 or sooner.


In October 2021, ULEZ will expand to cover all of London encircled by the North and South Circular, the city’s orbital arterial road network


Four times greater than the current low-emission zone, ULEX will not be able to rely on infrastructure for London’s congestion charge. Transport for London is exploring the option of integrating the ULEX into more sophisticated road pricing systems, which might include pricing based on congestion, emissions and distance, rather than the binary pricing model currently in place.


In total, the capital’s costs for ULEX are expected to reach £121m – although some estimates put the price at £700m. The lion’s share of spending, £54m, is due in the next financial year (2020/21). The start date of ULEX is fairly tightly fixed on October 2021. ­­In order to change the date or the scope of the expansion materially, a public and stakeholder consultation would have to be conducted.


As for ULEZ, early results are promising and offer other cities a guide on how to fairly swiftly make their vehicle fleet greener. The higher than expected ULEZ vehicle compliance is great news – suggesting travel behaviour does respond to pricing mechanisms to manage demand. Higher passenger income on London Underground and busses suggests that many are opting for public transport instead of the car. TfL is expected to publish more details on the impact of ULEZ on local air quality and travel behaviour in reports due in autumn 2019.


Watch this space for how the expansion to ULEX might kickstart further shifts in travel behaviour. Shutting down the residential exemption could further shift Londoners to sustainable modes of transport and free up precious public space used for parking.


Nicole Badstuber is an urban infrastructure researcher at the Centre for Digital Built Britain and University of Cambridge

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