Low Emission Bus Testing

This section provides a description of the testing and accreditation of Low Emission Buses (LEBs) and the documentation required to support this process.

LEB Certificates

In order to be eligible for grant funding from the Low Emission Bus scheme, a bus manufacturer must present local authorities or operators with a Low Emission Bus Certificate. Once a bus has undergone the LUB test cycle and met the required emissions targets. The data shown on the certificate is derived from an independently witnessed emissions test of a vehicle of a bus and calculation of the WTW GHG emissions savings of the bus. Where relevant, the number of miles of a LEB can operate in electric only mode will be identified. While every bus will be issued with a certificate, only one bus of that type will be required to be tested. Further details on the LEB certificate are provided in the LEB Certificates section.

Testing and Accreditation

The procedures for testing and accreditation of LEBs are based upon a type approval process. To determine whether a bus meets the minimum emission targets requires a whole vehicle emissions test, of both the potential Low Emission Bus and its diesel equivalent to calculate and compare their relative WTW GHG emissions. Using default emission factors for the fuel types used, WTW GHG emissions in grams per carbon dioxide equivalent can be calculated and compared. Further details can be found in the section on testing and accreditation procedures.

Well-to-Wheel and Well-to-Tank

'Well-to-Wheel' (WTW) is a value that includes all the emissions involved in the process of extraction/creation, processing and use of a fuel in a vehicle to gauge the total carbon impact of that fuel.  'Well-to-Tank' (WTT) only includes all the emissions associated with a fuel up to the point that it enters a vehicle's fuel tank or energy storage device (i.e. excludes tailpipe emissions). 

For the LUB test cycle, bus manufacturers (OEMs) seeking LEB status are asked to provide a 'WTT factor' with supporting evidence to show how much GHG emissions are emitted per litre or kWh of fuel that will be used with their bus.

Where OEMs cannot provide a factor, a Zemo Partnership default factor for the relevant fuel will be used. These default factors have been collated from the most recent national fuel statistics and reports.

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