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Can retrofit technology help fleets comply with CAZ, LEZ and ULEZ?

In this blog, find out if retrofit technology is the solution to help your fleet comply with Clean Air Zones (CAZ), Low Emission Zones (LEZ) and Ultra Low Emission Zones (ULEZ).

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Poor air quality is one of the largest environmental risks to public health in the UK and investing in cleaner air and doing more to tackle air pollution are high priorities for the UK Government. Road transport is responsible for approximately 68% of nitrogen oxides (NOx) concentrations at roadside with diesel vehicles being the largest source. These levels of air pollution remain an issue for our towns and cities. The World Health Organisation estimates that poor air quality leads to over four million premature deaths every year. To bring down the high levels of nitrogen dioxide we are experiencing, the introduction of CAZ, Low Emission Zones  and Ultra Low Emission Zones in London and other cities across the UK. 

These zones aim to deter the most polluting vehicles from entering certain areas within cities, and charge according to vehicle type, for example buses, coaches, taxis, HGVs.  

Other benefits of clean air zones include encouraging the uptake of low or zero emissions vehicles, such as electric vehicles and reducing traffic congestion in busy town and city centres. 

For more information on the zones in your area and the charges you might incur see our CAZ guide.  

Compliance options

  1. Avoid driving within the zone.
  2. Incur the charges if infrequent journeys are made and pass the cost to customers.
  3. Re-arrange operations by using vehicles that are compliant in a CAZ (e.g. Euro 4 petrol and Euro 6 or eCargo bikes and electric vehicles) and using non-compliant vehicles outside of the zone.
  4. Replace non-compliant vehicles with compliant ones.
  5. Look into retrofit solutions for diesel vehicles, involving an exhaust after-treatment system.

The final two options are the ones that actually help to reduce air pollution from vehicles, and are the most efficient in the long run 

Retrofit solutions

Retrofit solutions are used to bring down the emissions to Euro 6/VI equivalence. This involves fitting a diesel particulate filter (DPF) and a selective catalytic reduction (SCR) system with the urea (Adblue) injection. Once retrofitting is complete, air pollutant emissions are immediately reduced. 

Replace or retrofit

There are several factors that will impact the decision-making process of replacing or retrofitting a vehicle. These include cost of retrofitting, the cost of CAZ or LEZ charges, how long the vehicle has left in service, and the resale value of the vehicle before and after retrofit.  

The vehicles that are generally ‘ripe for retrofit’ are those that have a higher replacement cost and are on a fleet for longer. These are most likely to be specialist HGVs, buses and coaches rather than cars or vans.  

Assurance of retrofit suppliers

To ensure retrofitting suppliers and products are maintained to a high and trustworthy standard for operators, The Clean Vehicle Retrofit Accreditation Scheme (CVRAS) was set up. The scheme is administered by Energy Saving Trust on behalf of the Joint Air Quality Unit (JAQU) and with the support from Zemo Partnership. Since operating in 2017, over 10,000 vehicles have now been retrofitted under the scheme. 

To be approved by CVRAS, a company needs to have a recognised quality management system, comprehensive warranty provision and insurance cover. As well as proving their products meet the required emissions reduction for specific vehicles. As part of the scheme vehicles are tested over representative test drive cycles specific to the vehicle type e.g. HGVs, buses and coaches to ensure these standards are met.  

CVRAS approved suppliers

The following companies supply specific technologies needed for CVRAS such as Diesel Particulate Filters (DPF) and selective catalytic reduction systems (SCR): 

  • Eminox Ltd 
  • HJS Emission Technologies GmbH 
  • Cybrand AEC Ltd 
  • Proventia Oy 
  • Driveline Emission Technologies Ltd 

All suppliers are listed here.

How are retrofitted vehicles picked up in a CAZ?

Within a CAZ, automatic number plate recognition system (ANPR) cameras pick up compliant and non-compliant vehicles. A part of CVRAS, all approved suppliers will issue an individual vehicle installation record for each retrofitted vehicle.  An installation list is sent to Energy Saving Trust on a weekly basis and uploaded to the CAZ vehicle checker so when ANPR cameras pick up a registration they will automatically be checked against the DVLA and CVRAS database.  


For more information on CVRAS visit our support scheme page.