Understanding inputs and results¶

A calculation has three stages: choose vehicle inputs, calculate its physical performance, then calculate its life cycle inventory and impacts. The last stage includes production and energy supply as well as emissions during driving.

The words used in the guides¶

• Driving cycle: speed at each time step, with a road-gradient profile. Two tests with different speed or gradient profiles need not give the same consumption, even for the same vehicle.

• Curb mass: vehicle mass including onboard fuel, excluding people and cargo in this model. Driving mass adds people and cargo.

• Powertrain: the engine, motor and associated components that propel the vehicle. ICEV-p, ICEV-d and ICEV-g mean petrol, diesel and gas vehicles. BEV means battery electric; FCEV means hydrogen fuel-cell electric. HEV is a hybrid without plug-in charging; PHEV is a plug-in hybrid. Each package supports its own subset of these choices.

• Auxiliaries: equipment that uses energy without propelling the wheels, such as pumps, electronics and cabin heating or cooling. HVAC means heating, ventilation and air conditioning.

• Sample: one set of input values. A static calculation has one sample. Monte Carlo calculations draw several samples to explore specified uncertainty.

• Inventory: the quantities of materials, energy and emissions attributed to a vehicle or transport service. Foreground means the vehicle and supply processes assembled explicitly by the model. Background means the other supplying processes represented by database coefficients.

• LCIA: life cycle impact assessment, which converts inventory quantities into indicators such as climate change. An impact score is not a direct measurement of emissions from the vehicle.

• Proxy: a documented substitute used when a dataset for the exact vehicle, process or location is unavailable. Its suitability must be assessed for the study.

• Provenance: the record of data sources, assumptions, software versions and file checksums needed to trace a result.

Energy quantities are different measurements¶

For BEVs, charging electricity is usually measured on the alternating-current (AC) side of the charger. A battery DC measurement excludes charger losses. Do not compare the two directly or add charging losses to an output that already includes them. For a plug-in hybrid, report both fuel and purchased electricity, with the fraction of distance driven electrically. Its combined TtW energy is not a substitute for those two purchased-energy quantities.

Passenger cars and trucks use annual-average cabin heating and cooling inputs. Two-wheelers do not model cabin HVAC. All three reject ambient-temperature overrides. Buses support an outside temperature or twelve monthly values; their cabin-temperature assumption is fixed at 20 degrees Celsius. This restriction does not make bus heating and cooling independent of outside temperature.

Choosing a unit for life cycle impacts¶

The functional_unit argument specifies the transport service being compared:

• vkm: one vehicle travelling one kilometre.

• pkm: one passenger transported one kilometre. The vehicle result is divided by the modelled number of passengers.

• tkm: one tonne of cargo transported one kilometre. The vehicle result is divided by cargo mass in tonnes, not gross vehicle mass.

For example, 0.20 kg CO2-eq per vehicle-km with two passengers is 0.10 kg CO2-eq per passenger-km. This is an arithmetic example, not a model result. Active vehicles need a positive passenger or cargo load for these divisions.

Car, truck and two-wheeler cost outputs are per vehicle-kilometre. Bus cost outputs are per passenger-kilometre. Costs are financial estimates; they are not environmental impact indicators.

Reading a climate result¶

calculate_impacts() separates contributions along the impact axis. Select an impact_category before adding these contributions. Do not sum categories expressed in different units, or add results for different vehicles, years or samples unless that aggregation answers your study question.

In the bundled method="recipe", indicator="midpoint" set, the category climate change uses IPCC 2021, 100-year global warming potentials, excluding biogenic CO2. The selector names the collection of indicators; it does not mean that this climate row uses ReCiPe’s own climate factors. The separate climate change w bio category includes biogenic CO2.

A life cycle climate score includes manufacturing, energy supply, use and end-of-life contributions. It differs from tailpipe CO2 and from fuel consumption. Changing the background database can change the life cycle score while leaving vehicle mass and consumption unchanged.

Assessing confidence in a result¶

Verification checks that the program implements its equations and accounting correctly. Calibration adjusts an assumption using observations. Independent validation tests predictions against evidence not used to make that adjustment. A screening comparison is an initial comparison for which important conditions, such as route or test mass, do not fully match.

The difference reported in the comparison pages is 100 * (model - reported) / reported. Positive values mean the model is higher. This difference is not a confidence interval or a general measure of model accuracy. Several cycles or two meters on one vehicle do not constitute several independent vehicles. See Validation examples: what the comparisons show for concrete cases and Passenger-car calibration and validation for the detailed evidence.