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What is a Low Emission Bus?


The definition of a LEB was developed by LowCVP members and is based upon the combined Greenhouse Gas (GHG) emissions from the vehicle and from the fuel production. The definition is as follows:

“A Low Emission Bus produces 15% less Well-to-Wheel Greenhouse Gas emissions than an equivalent Euro V equivalent diesel bus of the same passenger capacity and have a Euro VI certified or equivalent engine."

There are a number of different technologies which qualify as a Low Emission Bus.

Eligibility Criteria

A bus must meet the following criteria to be eligible for funding from the Low Emission Bus Scheme:

  • A minimum of 15% GHG saving in WTW emissions compared to a Euro V diesel bus of equivalent passenger size.
  • Have a Euro VI certified engine or a proven equivalent level of emissions.

Key additional funding notes:

  • Additional funding will be awarded to buses which have part or full zero emission capabilities - a minimum operation of 2.5km with zero emissions.
  • Funding for fueling infrastructure may also be provided.

Baseline Target Calculations

LowCVP have calculate that the average Euro V diesel bus has WTW GHG emissions, expressed as a function of its passenger capacity, equal to the following:

WTW GHG (g/km) = 9.42 x Total Passenger Capacity + 480

The LEB emission baseline target is 15% less than the above formula and is equal to:

WTW GHG (g/km) = 8.00 x Total Passenger Capacity +408

Greenhouse Gases

The GHGs of interest as defined by the United Nations Framework Convention on Climate Change are Carbon Dioxide (CO2), Methane (CH4) and Nitrous Oxide (N2O). The contribution of these gases to the greenhouse effect is described as their Global Warming Potential (GWP), with CO2 used as the baseline to describe the relative strength of a molecule.

The table below defines the current GWPs defined for Methane and Nitrous Oxide: to convert grams of the pollutant to grams CO2 equivalent:


Carbon Dioxide (CO2)
Methane (CH4)
Nitrous Oxide (N20)
Global Warming Potential (GWP)

* Sourced from IPCC Assessment Report 4

Using carbon dioxide as a baseline allows us to use the measurement of grams of carbon dioxide equivalent or gCO2e to describe all the GHGs in one single figure, making a comparison of different fuels and technologies much simpler.

Well-to-Wheel Emissions

The Well-to-Wheel emissions is a sum of all the GHG emissions associated with all the energy used in the creation and combustion of a fuel. This incorporates the emissions released when the fuel is extracted from the 'well' through the refinement process to its transportation to the forecourt. These are known as Well-to-Tank (WTT) or indirect emissions.

To find more information on how a bus becomes a LEB, and how WTW emissions are calculated, visit the Testing and Accreditation page of this site.

For more information please contact: secretariat@lowcvp.org.uk or call 0207 304 6880

A member view...

The LowCVP’s strength lies in the breadth of its membership, wealth of information and a place to meet key industry contacts
Glenn Saint, Chief of Engineering and Manufacturing, Arrival