National low emission framework

Methodology for local authorities to undertake air quality assessment through the National Low Emission Framework (NLEF) to inform decisions on transport-related actions.

Appendix 1

Low Emission Zones


1.1 Low Emission Zones set an environmental limit on certain road spaces, allowing access to only the cleanest vehicles and can help to transform towns and cities into cleaner, healthier places to live, work and visit.

1.2 Vehicles that do not meet the emission standards set for a LEZ will not be able to enter the zone. A penalty charge will be payable by the vehicle's registered keeper where a non-compliant vehicle enters unless it is exempt.

1.3 Access to LEZs is usually based on Euro emission engine classification standards (Euro standards) which provide the emission rating of a vehicle including limits for Nitrogen Oxides (NOx) and Particulate Matter (PM).

1.4 LEZs can be a useful option to improve air quality although outcomes are dependent on size, vehicle scope, traffic data robustness and local metrology.

Emission standards

1.5 Euro standards define the acceptable limits for exhaust emissions of new vehicles sold in EU and EEA member states. The emission standards are defined in a series of European Union directives staging the progressive introduction of increasingly stringent standards.

1.6 Scottish LEZ restrictions will be based upon Euro standards, with the proposed minimum criteria likely to be:

  • Euro 6 for diesel cars
  • Euro 4 for petrol cars
  • Euro VI for buses and other heavy diesel vehicles (including older vehicles fitted with accredited retrofit technology).

1.7 The current proxy for determining the Euro standard of cars is to use age as a guide to the corresponding Euro classification:

  • the Euro 6 standard for diesel cars was introduced in September 2014, with any new car sold after September 2015 having to meet this standard
  • the Euro 4 standard for petrol engines was introduced in January 2005, with any new vehicles sold after January 2006 having to meet this standard

1.8 There is currently no reliable approach for basing a scheme on real world emissions performance and, whilst there are likely to be some 'gross polluters' in the vehicle fleet which are emitting proportionally more than the fleet generally, it is unlikely that these can be addressed through LEZs.

1.9 By prescribing minimum emission standards for each vehicle class, the emission standards applied within LEZs will be consistent across Scotland.

1.10 Vehicles which do not meet the specified emission standard will be subject to a penalty if they enter an LEZ unless they are covered by a specified exemption or meet other criteria such as an agreed retrofit standard or they are a zero or ultra-low emission vehicle.

1.11 In most LEZs, exemptions are available for certain vehicles which mean that they will not be subject to enforcement action if they enter the zone. These are often linked to the type of vehicle and its purpose e.g. emergency service vehicles or historic vehicles (vehicles with a 'historic' vehicle tax class).


1.12 In some cases, retrofitting a vehicle can provide an alternative to buying a new vehicle to meet the relevant emission standards. There are a range of retrofitting options for vehicles, which may be particularly important for buses. Retrofitting should be undertaken in accordance with an accredited scheme which can demonstrate that vehicles meet minimum requirements.

1.13 Retrofitted vehicles which meet the requirements of an approved accreditation scheme will be considered to be compliant with the LEZ requirements.


1.14 A grace period is a period during which entering the LEZ will not result in a penalty charge becoming payable. Grace periods can vary between vehicle types, with some vehicles required to comply with the emission standards ahead of others.

1.15 Grace periods can last for different lengths of time depending on the vehicle concerned and are usually between one and four years, running from the date of the scheme coming into effect. Often a longer period is allowed for residents who live within an LEZ.

1.16 In deciding on the appropriate grace period, consideration is given to the change needed in vehicle mix to meet the air quality aims, as well as the social, economic and health impacts of introducing the LEZ.

1.17 It is important that exemptions and grace periods do not undermine the objectives of the LEZ which is focused on improving air quality as soon as possible

Further information

1.18 Information on Scotland's LEZs can be found on the Low Emission Zones website.


Email: Andrew Taylor

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