Road tax and emissions go hand in hand. As awareness of climate change increased and it became a bigger priority for the UK, the road tax system was changed so you pay road tax based on the emissions your car produces. Cars are a major contributor to pollution, therefore this was an obvious answer to help reduce total emissions from cars and also to provide funding for schemes that promote greener alternatives.

When did Road Tax change to Emissions?

For cars first registered before March 2001 the road tax was based on engine size. The reason for basing tax on engine size was due to a few reasons:

  • Simplicity: Taxing vehicles based on engine size was relatively simple to implement and administer. Engine size was a readily available and easily measurable parameter, making it convenient for both vehicle owners and tax authorities.
  • Correlation with Road Wear and Tear: The rationale behind using engine size as a tax criterion was the belief that larger engines were often found in heavier and more powerful vehicles. These vehicles were thought to cause more wear and tear on the roads due to their weight and potentially higher speeds. Consequently, they were seen as requiring a higher contribution to road maintenance.
  • Revenue Generation: Taxing vehicles based on engine size also provided a stable source of revenue for road maintenance and infrastructure development. It allowed the government to collect funds from vehicle owners in a way that was relatively easy to predict and budget for.
  • Encouraging Fuel Efficiency: In some cases, engine size-based taxation was seen as a way to encourage fuel efficiency. Smaller engines typically consumed less fuel, which could lead to reduced emissions and lower fuel consumption. Vehicle owners opting for smaller engines might pay lower road tax, incentivizing the purchase of more fuel-efficient cars.

However in the years and months leading up to March 2001, it was becoming clearer how big an affect cars were having on the environment, therefore the decision was made to base road tax purely on the Co2 emissions of your vehicle. Any vehicle first registered after March 2001 but before April 2017 had its road tax based on emissions.

How do emissions affect what I pay in Road Tax?

Basically if your car was first registered after March 2001 but before April 2017 then your road tax will be calculated based on how polluting your car is. The more Co2 emissions it produces, the higher the rate of tax. This was changed in 2017 as the amount of pollution by newer cars was dropping significantly at this point.

To find out exactly how much each car should pay on Road Tax you can check our article How much should road tax cost me?

What percentage of emissions come from cars in the UK

The transport sector alone was responsible for 34% of total greenhouse gas emissions in the UK in 2022. Whilst it is hard to get exact numbers you can see that road transport is responsible for the majority of all emissions:

Vehicle TypePercentage of Total Transport Emissions in the UK (2021)
Car (Road)Approximately 70%
Bike (Cycling)Less than 1%
Plane (Aviation)Approximately 10%
Boat (Maritime)Approximately 7%
Rail (Railways)Approximately 3%
Other VehiclesApproximately 9%

Despite Planes being the worse contributor when it comes to a persons individual carbon footprint, you can see that cars are responsible for approximately 70% of all transport emissions in the UK.

In terms of total emissions of greenhouse gasses in the UK, cars and other road transport is responsible for approximately 23.8% of total UK emissions.

Do modern cars produce less emissions?

The short answer is yes, cars produced today are a lot more efficient and produce substantially less emissions. So much so that the government changed the road tax system again in 2017 as the levy was failing to raise enough funds due to cars producing such low emissions.

This chart shows how much more efficient cars have become since 1990:

road tax and emissions - greenhouse changes over last 20 years graph

What cars are the most polluting in the UK?

The following cars lead the pack in terms of greenhouse gasses produced. With this vehicles you can expect to pay a higher rate of road tax.

  1. Land Rover Range Rover Sport 3.0 HSE SDV6 A
  2. Bmw X5 xDrive30d M Sport Auto
  3. Mazda MX-5
  4. Bmw X3 XDrive20d M Sport Auto
  5. Ford Focus 1.6 Zetec Climate
  6. Ford Focus Hatchback 1.6 LX
  7. Vauxhall Zafira 1.6i Exclusiv
  8. Volkswagen Golf 2.0 GT TDI
  9. Nissan Qashqai Acenta 2.0 dCi
  10. Bmw 5-Series 520d SE Auto

Can you reduce emissions on a car?

There is a few things to do to reduce emissions on a car. These tips won’t help reduce your road tax but they will save your money and potentially increase the lifespan of your vehicle.

  • Unnecessary acceleration – We all know this type of driver, the kind who will put the accelerator to the floor at any opportunity they get, even if there is a car stopped 20 feet ahead of them. Well you really should not do this. In motorway traffic, rapid acceleration can cause a 15-30% decrease in fuel efficiency, in stop start traffic this ranges between 10-40%. Petrol costs a fortune these days, it is not something you want to waste. You will also reduce the risk of a collision if you avoid doing this.
  • Excess weight – The heavier your vehicle the harder it is to move, its simple science. If you are using your car as a travelling storage container and you can change that, you should. Reducing any excess weight will give you better fuel efficiency, it will also cause less wear on your vehicle.
  • Don’t speed – Vehicle fuel efficiency tends to start dropping once you go over 50mph. Simply put the faster you go the less fuel efficiency you have. Keep to the speed limit and you are more likely to fall within your cars optimal speed for fuel efficiency.
  • Drive less – The best thing you can do to reduce your cars carbon footprint is to simply not drive it when you don’t need to. We all have those moments where the walk would take 10 minutes but the drive only five. However these little journeys add up to a lot, whenever you decide to use your feet instead you help reduce greenhouse gas emissions, and get a little fitter too.

Whats worse for emissions, petrol or diesel?

Diesel was once heralded as a cleaner more efficient alternative to petrol, however this image has been tainted in recent years due to new findings about diesel cars.

Diesels tend to produce much less carbon dioxide than their petrol counterparts. Achieving the same performance for less fuel. However it has also been found that they produce more noxious gasses such as nitric oxide that are also harmful to the environment, whereas petrol produces almost none.

Nitric oxide can cause respiratory problems so clearly this is a bit of an issue. If you have a good particulate gas filter in your exhaust you can make your car a lot greener, however these filters need to be of a high quality and be regularly maintained to stay effective.

road tax and emissions - electric car which is exempt from road tax

Electric cars and Road Tax

Currently if you own a zero emission or electric vehicle you are exempt from paying any road tax. This is due to the fact that your car does not produce any emissions.

However beginning in April 2025 this exemption will end. The reason for this is that government does not want the money raised from road tax to drop too much and more zero emission vehicles are expected to be on the roads by this point.

The changes are expected to work as follows:

  • In the first year you can expect to lowest first year rate of road tax which is currently £10 per year.
  • After the first year you can expect to pay the flat rate road tax which is currently £180 per year.


The UK’s road tax system transitioned from engine size-based taxation to emissions-based taxation for cars registered after March 2001 but before April 2017, aiming to reduce pollution. In 2017, it changed again due to modern cars producing fewer emissions.

Cars were responsible for around 70% of transport emissions and 23.8% of total greenhouse gas emissions in the UK. Modern vehicles are more efficient and environmentally friendly.

Diesel cars, once considered cleaner, produce more noxious gases.

Zero-emission and electric vehicles were initially exempt from road tax but will face a low flat rate starting in April 2025 to maintain funding.

Find out more about Road Tax

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