Guidance

Modifying your vehicle’s emissions: the legal, safety and health implications

Published 2 February 2018

The law

Under the Road Vehicles (Construction and Use) Regulations (Regulations 61(7) and 61A(3)) and the Road Traffic Act 1988 (Section 42) it is an offence to use on a road a vehicle which has been modified in such a way that it no longer complies with the air pollutant emissions standards it was designed to meet.

The potential penalties are £1,000 for a car and £2,500 for a van, lorry or bus.

Under the Road Traffic Act 1988 (Section 75) it is an offence to alter a vehicle in such a way that the use of the vehicle on a road would be unlawful. A person altering the vehicle (if they knew or believed that the vehicle would be used on the road) could be found guilty of an offence under the Act.

Potential penalties are unlimited fines.

The UK has a long tradition of allowing vehicle owners relative freedom to change their vehicles to suit their specific requirements, subject to ongoing compliance with the relevant UK construction standards. These changes may be purely cosmetic, or to improve the usability of the vehicle for its owner, or to alter its performance.

There are, however, circumstances where modifications may result in legal, safety and/or health implications for the vehicle owner, its occupants, other road users, and the wider population. The key message is that even if you think you know what you’re doing, if making modifications yourself, there can still be unintended consequences. It is advisable to have any work checked by a competent professional mechanic and ensure you stay safe and within the law.

Making changes to the engine management, emissions control, exhaust or braking systems carry the highest risk of unintended consequences.

Legal implications

A person using (or causing or permitting to be used) a vehicle on the public road, which does not comply with the emissions standards it was designed to meet, is committing an offence.

All vehicle owners should be aware of the need to inform their insurers of modifications made to the vehicle, whatever form these might take, as changes to the vehicle potentially alter the risk being insured.

It is not always obvious to vehicle owners that some modifications will make the vehicle illegal to use on the road, irrespective of whether the insurer is prepared to provide cover. For example, removing a catalytic converter or diesel particulate filter will almost certainly result in a vehicle’s emissions exceeding type approval limits and make the vehicle illegal to drive on the road. Engine re-mapping may also result in non-compliant emissions.

It is the driver who is responsible for ensuring compliance.

Safety implications

A badly modified vehicle has the potential to kill its occupants and pollute the air. Making changes to the engine management system in an attempt to increase performance, coupled with the removal of all or part of the emissions control system, may lead to significantly higher levels of harmful exhaust emissions which can then find their way into the vehicle’s interior. Incorrectly fitted parts or unapproved changes to a vehicle can lead to a potentially deadly outcome for vehicle occupants.

Health implications

Emissions standards for cars have become increasingly stringent in order to protect public health and improve air quality. Measures to tackle pollutants such as nitrogen oxides, carbon monoxide and particulate matter have been developed by vehicle manufacturers. They involve increasingly complex engine management systems, and use of technologies such as exhaust gas recirculation, catalytic converters, diesel particulate filters and selective catalyst reduction systems.

Tampering with or removing emissions control equipment can result in substantial increases in toxic exhaust gases:

• carbon monoxide – a colourless, odourless and tasteless gas that is highly toxic and is one of the most common causes of fatal poisoning, accounting for around 25 deaths a year in the UK

• nitrogen dioxide – a nasty smelling gas which can irritate the eyes and lungs, reducing immunity to lung infections
  • its effects are estimated to be equivalent to nearly 23,500 deaths in the UK per year
  • it contributes as well to the formation of photochemical smog, with a significant impact on human health
• particulate matter – tiny pieces of solid particles and liquid droplets which when inhaled can cause serious health effects
  • particulate matter contributes to the risk of developing cardiovascular diseases and lung cancer and its effects are estimated to be equivalent to nearly 29,000 early deaths in the UK

What are the warning signs to look out for?

You may not be able to tell whether a car’s emissions have been modified – if in doubt ask a competent professional mechanic to check.

An ‘engine check’ malfunction indicator light on the dashboard may indicate a serious problem with the emissions control of the vehicle – get it checked out and do not ignore it, even if the vehicle seems to perform normally. A strong smell of fuel may indicate a leak or that the engine is running rich (ie with too much fuel). You should get this checked immediately.

Smoke from the exhaust should not be visible under normal driving conditions on vehicles fitted with pollution control technology. The engine may be becoming worn, or parts may be missing or faulty.

Legal information

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