Testing & Accreditation Procedures
In order to be accredited as a Low Carbon Emission Bus, vehicles must have GHG emissions that achieve the target determined for their maximum passenger carrying capacity. Buses with GHG emissions higher than that corresponding to its passenger capacity will not be afforded Low Carbon Emission Bus status.
The GHG emissions are measured against a whole vehicle emissions test, on an appropriate chassis dynamometer, to the LowCVP Low Carbon Bus test requirements. The LowCVP members developed the testing and accreditation procedures for LCEBs. There are four separate sets of procedures which relate to the testing of the following types of vehicles which are available for download;
Low Carbon Emission Bus status will be conferred on all vehicles similar to those presented for test, as long as the vehicles use similar fuels and energy management strategies.
Determining the GHG emissions
To determine whether a bus is a LCEB, a two step procedure is used. Firstly, a whole vehicle test is undertaken to measure the tank-to-wheel emissions and energy consumption. Secondly, the results of the whole vehicle test will be used to calculate the Well-to-Wheel (WTW) emissions. This will then be used to compare with the target line to determine whether the bus meets the criteria of a LCEB.
Whole vehicle test -The whole vehicle test, which measures Tank-to-Wheel (TTW) emissions, may be carried out at any competent and independent emission test centre. The test must use either the Millbrook London Transport Bus (MLTB) test cycle, based on Route 159 in London, or an equivalent alternative test cycle. If an alternative test cycle is used, it must be based on a similar average speed as the MLTB test and have a similar number of stops per kilometre. Any non-MLTB test must be approved in the advance by the Department for Transport.
The Greenhouse Gases (GHG) of interest are Carbon Dioxide (CO2) Methane (CH4) and Nitrous Oxide (N2O).The gas values of methane and nitrous oxide, if measured, will be converted to carbon dioxide equivalent based upon their global warming potential and added to the carbon dioxide emissions to provide a CO2 equivalent g/km figure.
The relative global warming potentials for CO2, CH4 and N2O are 1:21:310 respectively.
Well-to-wheel emissions - The results of the whole vehicle test, or TTW emissions, will be used to calculate the CO2 equivalent emissions performance of the vehicle on a WTW basis appropriate to the fuel as used in the approval test and as used in service. In the case of biodiesel the fuel pathway used will be that of diesel to avoid BSOG providing an incentive over and above the incentive provided by the RTFO.
The WTW emissions are the sum of Tank-to-Wheel (TTW) and the Well-to-Tank (WTT) performance with CO2 equivalent emissions expressed as CO2 equivalent grams per kilometre, this is then assessed against maximum passenger carrying capacity.
The Well-to-Tank (WTT) emissions and energy consumption will be determined using an appropriate analysis such as those carried out by CONCAWE or by L-B-Systemtechnik GmbH or similar body, subject to approval by the Department for Transport. The results are expressed in grams of carbon dioxide equivalent per MJ of fuel delivered. Knowing the fuel consumption of a vehicle in MJ/km, the WTT CO2 equivalent figure can be expressed in g/km.