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Clean Vehicle Retrofit Accreditation Scheme (CVRAS)

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What is the Clean Vehicle Retrofit Accreditation Scheme (CVRAS)?

The CVRAS is a robust certification scheme for manufacturers of retrofit emissions reduction technology that will enable Clean Air Zone (CAZ) compliance of legacy fleet vehicles.

This certification scheme supports the operation of Clean Air Zones and addresses the air pollution emissions from buses, coaches, heavy goods vehicles, mini-buses, taxis and vans. To learn more about CVRAS, download a free copy of LowCVP's Clean Vehicle Retrofit Technology Guide.

CVRAS Register: Approved manufacturers and devices

The CVRAS Register filters what approved companies and emission reduction systems suit your vehicles best, based on make, model and engine type. 

This tool contains details of companies and their systems approved under the scheme requirements along with their contact information and the categories of vehicle to which their systems can be applied in order to make the vehicle Clean Air Zone compliant.

Use the CVRAS Register now 

Download a full list of approved manufacturers and devices, or a list of products the respective company no longer wants to be listed as available to the market.


CVRAS Retrofit Vehicle Type Overview


Retrofit solutions for buses are well established. Exhaust after-treatment systems combining diesel particulate filter (DPF) and selective catalytic reduction (SCR) technology are the most widely applied. Other technologies include re-powering, where the old engine is replaced with a new engine with lower emissions, such as replacing diesel engine with an electric or hybrid drivetrain.

There are currently a number of suppliers approved to provide these systems.


Similar to buses, there is diesal particulate filter (DPF) and selective catalytic reduction (SCR) technology applicable to coach retrofit applications. These systems are tested on specific coach test cycle protocol.

Heavy Goods Vehicles (HGVs)

This vehicle category is particularly challenging in terms of retrofit technology due to the diverse range of vehicles, engines and duty cycles out there in a legacy fleet.

Diesel particulate filter (DPF) and selective catalytic reduction (SCR) technology is still applicable and is used on the majority of new trucks coming off the production line today, as are re-powering solutions.

We have set the test protocol and limits for HGV applicable retrofits and expect to see applications being submitted in the near future. The determining factor in regards to which retrofit system to develop and test is whether a market will materialise for the system. Operators, their associations, local authorities and retrofit solution providers need to collaborate in order to focus developments on the applications that require a retrofit solution.

Refuse Collection Vehicles (RCVs)

One of the most challenging vehicle types in terms of emissions performance are refuse collection vehicles (RCVs). This is because their slow speed stop-start operation pushes exhaust after-treatment systems to the limit.

However, there are retrofit system suppliers that have demonstrated Euro 6 equivalence or better, and are currently going through the approval process.

Another potential retrofit solution for RCVs is electrification, and there is currently a system provider going through the CVRAS approval process.  


Vans were one of the last vehicle categories to adopt the Euro 6 emissions standards, which means there are more Euro 5 diesel vans out there in legacy fleets.

In general, the cost to replace a van is lower, unless it is a highly specialised conversion. This, combined with the fact that retrofit solutions can be relatively high in cost and difficult to fit, means that it is often cheaper to replace than to retrofit vans.

In order to comply with an Ultra Low Emissions Zone (ULEZ), Clean Air Zone (CAZ) or Low Emissions Zone (LEZ), there is the potential to purchase a second-hand Euro 4 petrol van, if appropriate for the purpose of the vehicle. For these reasons, it is expected that retrofit solutions will only be provided for niche or highly specialised circumstances, and replacement will be the compliance option of choice. One area of opportunity will be the electrification or re-power of vans as a retrofit solution.

We look forward to receiving CVRAS applications for vans as the standards and test protocols are set.

Black Cabs

Black cabs (London taxis) can be subject to specific requirements from licensing authorities and, in some cases, can be exempt from Ultra Low Emissions Zone (ULEZ), Clean Air Zone (CAZ) or Low Emissions Zone (LEZ) standards. But they can also be significant emitters of local pollution, which is why retrofit solutions that reduce emissions are encouraged to apply for CVRAS approval.

There is currently one solution that is CVRAS approved which involves re-powering combined with alternative fuel conversion (LPG).

Passenger Cars

Due to the cost of a retrofit exhaust after-treatment system and the complexity to fit within passenger vehicles, retrofit will not be an economically viable option for most vehicle owners. Purchasing a second-hand Euro 4 petrol car could be the most economical solution.

The CVRAS is open to receive applications from retrofit system suppliers with the test protocol and standards set (the same as for vans), however consumers should be aware that only CVRAS approved systems will be recognised by local authorities implementing an Ultra Low Emissions Zone (ULEZ), Clean Air Zone (CAZ) or Low Emissions Zone (LEZ).


The Energy Saving Trust has withdrawn the Clean Vehicle Retrofit Accreditation Scheme accreditation from GreenUrban Technologies after discrepancies between reported and actual test results were identified during a routine audit.

In total, 16 retrofitted buses belonging to three separate companies have so far been identified as having been affected. Energy Saving Trust is working to identify any other vehicles and companies that may have been affected, and we will work closely with those affected to resolve the issue.

We are supported in this decision by our joint owners of the scheme, the Low Carbon Vehicle Partnership (LowCVP).



Getting certified

Manufacturers of abatement equipment need to get their equipment accredited by the Energy Saving Trust before it can be added to the list of approved devices available to vehicle and Clean Air Zone (CAZ) scheme operators. This ensures that approved filters meet minimum technical standards and that vehicles fitting these approved emission reduction systems meet the national CAZ emissions standards.

Potential applicants should be aware that emission reduction systems and technologies will be required to demonstrate robust technical performance in order to be eligible for approval and manufacturers are required to operate quality management systems to certified standards, for example, ISO 9001. Please see the scheme documentation below for further details.

Scheme documentation and information

Contact our experts

Speak with our Transport Certification team via email or call +44 (0)20 7222 0101 for more details.

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Contact our team

For more information on the Clean Vehicle Retrofit Accreditation Scheme (CVRAS), please contact our Transport Certification experts.