In 2009 - 2011, a comprehensive project on urban buses was
carried out in cooperation with IEA's Implementing Agreements
on Alternative Motor Fuels and Bioenergy, with input from
additional IEA Implementing Agreements. The objective of the
project was to generate unbiased and solid data for use by policy-
and decision-makers responsible for public transport using buses.
The project comprised four major parts: (1) a well-to-tank (WTT)
assessment of alternative fuel pathways, (2) an assessment of bus
end-use (tank-to-wheel, TTW) performance, (3) combining WTT and TTW
data into well-to-wheel (WTW) data and (4) a cost assessment,
including indirect as well as direct costs.
Experts at Argonne National Laboratory, Natural Resources Canada
and VTT worked on the WTT part. In the TTW part, Environment Canada
and VTT generated emission and fuel consumption data by running 21
different buses on chassis dynamometers, generating data for some
180 combinations of vehicle, fuel and driving cycle. The fuels
covered included diesel, synthetic diesel, various types of
biodiesel fuels, additive treated ethanol, methane and DME. Six
different hybrid vehicles were included in the vehicle matrix. The
TTW work was topped off by on-road measurements (AVL MTC) as well
as some engine dynamometer work (von Thünen Institute).
Over the last 15 years, tightening emission regulations and
improved engine and exhaust after-treatment technology have reduced
regulated emissions by a factor of 10:1 and particulate numbers
with a factor of 100:1. Hybridization or light-weighting reduce
fuel consumption 20 - 30%, but otherwise the improvements in fuel
efficiency have not been so spectacular. The driving cycle affects
regulated emissions and fuel consumption by a factor of 5:1. The
fuel effects are at maximum 2.5:1 for regulated emissions
(particulates), but as high as 100:1 for WTW greenhouse emissions.
WTW energy use varies with a factor on 2.5:1.
