Greenhouse Gases (Carbon Footprint)
The KPI specified for greenhouse gases is the emissions of CO2-equivalent, as it
takes into consideration emissions of other-than-CO2 greenhouse gases. The unit is
grams of CO2 per tonne-km. Because the ‘‘price’’ of a tonne of CO2 may fluctuate
in time, emissions themselves are preferred to estimates of the relevant external
costs for corridor assessment. Following the NTM tool logic on system boundaries
(Appendix A), the system boundary B (well-to-wheel) is selected for this application,
provided of course that the necessary data is readily available.
The chosen indicator is in reality a composite, its value being produced from
those of three PIs according to the formula:
Specific emissions of GHG = (Fuel Emission Factor)*(Specific energy
consumption)/(load factor)
The Fuel Emission Factor expresses emissions of GHG per energy unit of fuel
and is measured in grams CO2-eq/kWh. It depends on the type of fuel being used.
The Specific Energy Consumption, the energy input to the vehicle (or vessel) per
unit distance travelled, is measured in kWh/km. It is influenced by engine and
vehicle technology, driving conditions (speed, congestion, topography, weather,
driving pattern) and by load factors. Finally, the Load factor (capacity utilization
factor) describes the cargo load in tons relative to the capacity of the vehicle/
vessel, in ton-km/vehicle-km.