Can low emissions zones effectively regulate traffic in cities? 

TomTom's Andy Marchant explores the impact and the future of LEZs

Low-emission zones (LEZ) have become a common feature in modern cities. They are an effective technique for managing traffic flow and ensuring that drivers of older, higher polluting vehicles are deterred from driving into city areas by imposing tariffs and fines. Electric vehicles and other newer, cleaner modes of transportation are allowed to easily enter and exit LEZs.

The first of two emission zones in London, which was implemented in 2008, spans a vast area and only applies to commercial vehicles. The second is a smaller ultra-low emission zone that was implemented in 2019 and is designed to limit the movement of all cars in Central London.

Paris was one of France’s first cities to establish low-emission zones. The French capital began exploring measures to minimise traffic-related emissions in 2015 and has since established various ecological zones that control the movement of high-polluting vehicles.

In 2019, Amsterdam implemented a low-emission zone that encompasses the region within the city’s primary ring road, the A10. Based on their emissions, this zone prohibits certain types of diesel-powered automobiles, buses, vans, and trucks. Those who do not follow the guidelines could face fines ranging from €70 (US$77.50) to €250.

Low Emission Zone (LEZ)
A number of big cities have implemented LEZs and ULEZs, and with a notable impact on emissions

Do they make a difference?

Generally speaking, LEZs have been proven to make a considerable difference to the levels of pollutants and greenhouse gases in cities, in terms of both CO2 but also NOx and particulate matter. This isn’t surprising given that the worst polluting vehicles are the hardest penalised for entering a low emission zone, if they’re not banned entirely.

Before diving into the data, it’s important to note the difference between CO2 and NOx and PM. CO2 is a greenhouse gas and is detrimental to the environment, whereas NOx and PM are pollutants, which are more directly harmful to human health. In recent years, LEZs have focused on reducing pollutants, and less so on CO2. Strict legislation on engine emissions has targeted CO2 production for more than two decades.

Are they effective?

By placing traffic data alongside an emissions model, data also shows how valuable LEZs in city centres can be. The impact that LEZs in Paris, Amsterdam, Berlin and London are having on CO2, NOx and particulate matter (PM) pollution is evident. In Amsterdam, the city’s LEZ is effectively cutting the production of CO2 by 0.4%, NOx by 8% and particulate matter pollution by 27%. That’s 1 tonne of CO2, 63kg of NOx and 4kg of particulate matter, per day. Paris’ LEZ cuts CO2 by 0.4% (32 tonnes per day), NOx by 7% (2,029kg per day) and PM pollution by 35% (124kg per day).

Berlin’s LEZ effectively cuts CO2 pollution by 0.3% (7 tonnes per day), NOx by 8% (465kg per day) and particulate matter by a staggering 33% (22kg per day). In London, we also see one of those effective LEZs. The English capital’s highly restrictive but small ULEZ (ultra-low emission zone) cuts CO2 by 5% (42 tonnes per day), NOx by 54% (1,616kg per day) and particulate matter by 45% (14kg per day).

Although LEZs are having a significant influence, the best hope for them is that they become irrelevant

One might ask why LEZ don’t seem to cut CO2 as much as NOx or PM pollution, but when we consider how most of these LEZ work, the answer is quite clear. Most low emission zones focus on pollutants (NOx and PM), which heavily penalises diesel vehicles, and commercial vehicles such as trucks and vans in particular.

Relatively speaking, diesel vehicles produce less CO2 per km than comparable gasoline-engine vehicles. Given that gasoline-engine vehicles aren’t as heavily penalised for entering a LEZ, CO2 emissions in the LEZ aren’t significantly lower than outside. However, diesel vehicles do produce a lot of NOx and PM pollution; the heavier the vehicle, the worse it gets. As LEZs aim to keep diesel vehicles out of city centres, this has a more pronounced impact on the level of NOx and PM pollution; hence the more dramatic percentage reduction of NOx and PM.

With the upcoming EU7 engine regulations, which come into force in 2025, we should see more dramatic reductions of CO2. Where EU5 and EU6 regulations focused heavily on encouraging carmakers to develop low NOx and low PM engines, EU7 regulations will tighten limits on how much CO2 engines are allowed to produce.

Traffic congestion
LEZs influence the mix of vehicles within the zone, but do they address traffic volumes?

Calculating the benefit of LEZs

When a LEZ is in operation, it influences the vehicle mix inside the zone compared to outside the zone. Inside the zone, the proportion of diesel vehicles drop and electric vehicles increase, for example, which then affects the volume of emissions produced. By comparing how the vehicle fleet changes, it is possible to estimate the impact that LEZs have on pollutant production.

This can be calculated by considering the mix of vehicles outside the low emission zone (but still within the city). It then applies this mix of gasoline, diesel, hybrid and electric vehicles to the traffic volumes seen inside the LEZ to estimate what emissions would be if no LEZ was enforced. It compares this estimate to what the real-world vehicle mix was when a LEZ zone is enforced. It should be noted that this model assumes the LEZ doesn’t affect volume of traffic.

The future of LEZs

Although LEZs are having a significant influence, the best hope for them is that they become irrelevant. By 2030, Paris’ low-emission zone would not just restrict but outright prohibit combustion-engine vehicles from entering the city.

LEZs will likely become less relevant in places that do not take such a severe position against combustion engine vehicles as the number of electric vehicles grows naturally in conjunction with other restrictions that prohibit the sale of combustion engine vehicles. The difficulty for city planners will shift as a result of this.

There will be no emissions-based constraints stopping EVs from entering cities if they become the norm. Even if there are no tailpipe emissions, there is a chance that this will increase inner-city congestion. It’s a problem that shouldn’t be ignored. If this is the case, it is reasonable to expect things like London’s Congestion Zone charge to take the place of the LEZ as the main topic of discussion when it comes to affecting traffic movement in our cities. Other cities will almost certainly follow suit with higher congestion fees.


About the author: Andy Marchant is Traffic Expert at TomTom

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