London’s Ultra-Low Emission Zone prevents the most polluting vehicles from entering the city center.
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 penalizes diesel vehicles, and commercial vehicles such as trucks and vans in particular.
Relatively speaking, diesel vehicles produce less CO2 per km than comparable petrol-engine vehicles. Given that petrol-engine vehicles aren’t as heavily penalized 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 low emission zones keep diesel vehicles out of city centers, 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.
How TomTom calculates 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, we see 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 TomTom can estimate the impact that LEZ have on pollutant production.
TomTom does this by considering the mix of vehicles outside the low emission zone (but still within the city). It then applies this mix of petrol, 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 when a low emission zone is enforced.
It should be noted that this model assumes the LEZ doesn’t affect volume of traffic. TomTom bases its estimates on volumes of traffic inside the LEZ for a typical day. For the company’s full methodology, click here.
The future of low emission zones
Even though Low Emission Zones are proving to make a dramatic impact, the best thing we can hope for them is that they become irrelevant.
In Paris, by 2030, its low emission zone won’t restrict the movement of combustion engine cars, it will outright ban them from entering the city.