1.1 Cargo calculations
NTMCalc is able to calculate emission levels and energy use for a wide variety of transport activities, and this section explains the key points on how to specify and calculate these activities.
A calculation object is a “thing” that can be subject of a calculation. The most common calculation objects in NTMCalc are vehicle types or vehicle classes, e.g. “Rigid truck 7.5 – 12t”, “Electric train” or “Oil tanker”. Other examples of calculation objects are terminals and fuels.
A transport activity is the combination of a specific calculation object (e.g. “Rigid truck 7.5 – 12t”) and a specific calculation model (e.g. “Shipment transport”) The calculation model determines the type of calculation that will be performed on the selected object. There are a number of calculation models available in NTMCalc Freight Advanced:
- Shipment transport – single shipment. Calculation of emission levels, fuel consumption and energy use for the transport of a single shipment which is specified by size and transport distance. Size can be measured by weight, volume or volumetric weight.
- Shipment transport – multiple shipments. Calculation for the summary transport effort, measured in tonne-kilometres, of multiple shipments.
- Vehicle operation. Calculation for the operation (running) of a vehicle for a specific distance, or running a vehicle on a specific amount of fuel.
- Fuel combustion. Given the gross fuel consumption for a single fuel or mix of fuels, with quantities taken from the fuel bills or other sources, the system will calculate the total amount of climate gas being produced and the total amount of energy being used.
- Execution of activity or service related to a transport. Emissions and energy calculations for various services and cargo handling activities such as refrigeration, loading and unloading of cargo.
The table below shows the available calculation models for each transport mode.
As seen in the table, not all calculation models apply to all transport modes. The explanation for this is that the underlying computation models of the four transport modes are very different. For instance, the reason why “Shipment transport – summary level” does not apply to aircrafts is that aircraft fuel consumption is not linear to the flight distance (take-off and landing consumes more fuel per km than cruising), so the distance must always be made explicit in aircraft calculations.
Life cycle calculations
NTMCalc calculations include the following life cycle stages:
- Well-to-Tank (WTT) which covers extraction, production and distribution of fuel. It is optional to include WTT in the calculations (step 1 in the Transport Activity Specification Wizard).
- Tank-to-Wheel (TTW) which covers fuel use in the vehicle.
The full fuel cycle, Well-to-Wheel (WTW), is obtained by adding WTT and TTW.
WTT, TTW and WTW are, for each transport activity, accounted for separately in the result report
The system provides default data for all parameter settings and input fields of the wizard except those related to shipment size, distance and consumed amount of fuel. A default setting or data reflects what would be the average, most common or typical case. Please note that a specific default setting or value will depend on input from previous steps (e.g. fuel consumption for trucks in step 4 depends on the parameter settings in step 2 together with the cargo load factor entered in step 3), and that setting or value may change as a result of going back and chancing any of the previous input. The system may not only alter a previous default value but also a custom value entered by the user, e.g. if the user changes the fuel consumption value for a truck in step 4 and then goes back to change a parameter setting in step 2 (fuel type, road type, euro class, etc) the system will recalculate the fuel consumption and overwrite whatever value the user has entered.
The term shipment is defined as cargo transported under the terms of a single bill of lading or air waybill, irrespective of the quantity or number of containers, packages, or pieces. Or simpler: a load of goods that are being sent to a customer, store, etc. It is assumed that shipment transports are undertaken in a shared transport system where the capacity of a vehicle (or set of vehicles) can be shared between multiple shipments. A shipment is therefore only allocated the part of the emissions that emanates from its share. The general allocation formula is:
Allocation factor = Shipment size / (Cargo load factor * Cargo carrier capacity) where:
- Shipment size is the size of the shipment that is subject of the transport.
- Cargo carrier capacity is the maximum load capacity of the vehicle.
- Cargo load factor is the portion (percentage) of the vehicle’s cargo carrier capacity that is actually utilized.
The gross emissions of the vehicle are multiplied by the Allocation factor to calculate the share of the shipment. Note that the Allocation factor will be grater than 1 if the size of the shipment is larger than the actual load capacity of a single vehicle (Cargo carrior capacity * Cargo load factor). This means that more than one vehicle can be used for a single shipment transport.
Also note that neither Cargo carrier capacity nor Cargo load factor can be set to 0 (zero) since this would lead to division by zero, which is not defined. While at first glance it may seem desirable to be able to set Cargo load factor to zero to account for empty loads, it would not be logical to carry a shipment on a vehicle with a load factor of 0 %. To deal with empty loads, use the vehicle operation model instead.
Shipment size by weight or volume (single shipment)
This model calculates a shipment transport where sizing and allocation is based on cargo weight or cargo volume. Note that allocation based on weight alone can be misleading or unfair for cargo of low density. If both the volume and the weight of the shipment are known, a more fair allocation may be achieved by using the volumetric weight model.
Shipment size by volumetric weight (single shipment)
This calculation model is based on commercial cost calculation principles where the cost of transporting a shipment can be affected by the amount of space that it occupies, and not just the actual weight.The cost (the allocation factor in our case) is based on the volumetric (or dimensional) weight of the shipment.This is calculated by multiplying the volume with the volumetric factor (typical value is 0.25 tonnes/m3).The result is compared with the actual weight of the shipment to ascertain which is greater; the higher weight is used to determine the allocation factor. The allocation principles for volumetric weight is the same as for volume or weight, but with the important distinction that the Cargo load factor must be calculated from cargo volumetric weight.
Transport effort by tonne-kilometres (multiple shipments)
This model calculates the emissions and energy use at a summary level, i.e. the summary transport effort, measured in tonne-kilometres, of multiple shipment transports. The summary effort is the sum of the individual efforts of all shipment transports involved. Individual effort is calculated by multiplying the shipment weight by the distance.
Just as for single shipments it is assumed that that the transports are undertaken in a shared transport system where the capacity of a vehicle (or set of vehicles) can be shared between multiple shipments. Allocation is done according to the principles explained above.
This model calculates the gross emissions and energy use generated by the running (operation) of a vehicle for a specific distance, or running a vehicle on a specific amount of fuel. Note that no allocation is done since this calculation model is not concerned with shipments. The system will ask for the Cargo load factor but this is used for emissions calculation only and not for allocation purposes (in general a heavier loaded vehicle will consume more fuel and produce more emissions).
Please refer to the section about numerical data for a general description of numerical data formats and data accuracy.
Allowed formats and values
- Decimal notation (12.3, 0.005, etc) or scientific notation (12.5E3, 6.67E10, etc) can be used.
- Generally, any positive decimal number (including zero) is allowed. Any constraint to this is noted to the left (after the unit).
- Generally in percent (%) fields, any positive decimal number between and including 0 and 100 is allowed. Any constraint to this is noted to the left (after the unit).
Any numerical input is considered to be a rounded value. In order to be able to provide correct rounding in the final output, the system will determine the number of significant figures of the input value. Note that trailing zeroes are always significant in input data (which is not the case with output data). Examples
- 123.0 (4 significant digits – all trailing zeroes are significant)
- 12000 (5 significant digits – all trailing zeroes are significant)
- 0.0670 (3 significant digits – leading zeroes are non-significant)
- 1.2E5 (2 significant digits)
NTMCalc provides the following reports:
- On-screen report including both summary and individual levels of all the transport activities that have been entered.
- PDF for print-out and to serve as appendices. This report does not only display the numbers of the on-screen report, but also includes information about all settings for each transport activity.
- CSV file export enabling further data processing and analysis in other tools (e.g. Excel).
The NTMcalc emission report includes the following compounds:
- CO2fossil – carbon dioxide of fossil origin
- CO2biogen – carbon dioxide of non-fossil origin
- CO2total – total CO2 (CO2fossil + CO2biogen)
- CO2e – total greenhouse gases measured as carbon dioxide equivalents, includes fossil carbon dioxide, methane (CH4) and nitrous oxide (N2O)
- SO2 – sulfur dioxide
- NOx – nitrogen oxides
- N2O – nitrous oxide
- CH4 – methane
- HC – hydrocarbons (includes CH4)
- PM – particulate matter
NTMcalc reports energy use as:
- Energy – primary energy use
- Fuel consumption (where applicable) – amount of fuel (energy carrier) consumed
- Electricity consumption (where applicable) – amount of electricity generated at the power plant
Please refer to the section about numerical data for a general description of numerical data formats and data accuracy.
- For output data the user has the option to specify the number of digits to be displayed or have the system display data with the number of significant figures that is allowed for in regard to the precision of input data.
- The trailing zeroes of an integer are not significant (as opposed to the interpretation of input data). Example:
- 12000 (2 significant digits – trailing zeroes of integers are not significant)
- 123.0 (4 significant digits – all trailing zeroes of decimal numbers are significant)
- 12.000E3 (5 significant digits – all trailing zeroes of decimal numbers are significant)
All arithmetic operations are completed before any rounding takes place. Because of this it might at times, especially if the number of displayed digits are low, appear as the system does not perform arithmetics correctly: – e.g. the values 13.4 and 12.3 sum up to 25.7 but when the numbers are rounded to two digits it will look as 12 and 13 sum up to 26. Both the arithmetic and the rounding operations are in fact performed correctly, but with only two digits displayed the intuitive perception is that the math is bad. To convince oneself that the numbers are correct, the number of displayed digits can be increased.
Unknown quantities: >0
It is the intention to maintain a standard set of coherent emission figures for all transport activities in the system, but for practical reasons this is not always possible (e.g. lack of research on specific fuels or emissions). This can pose a problem when the emissions of all legs in a transport chain are being summarized into a grand total; if the data for specific emission is unknown (and therefore missing in the database) for one of the legs it would be incorrect to calculate the total sum since this would include an unknown value. This problem is managed by introducing the concept of unknown quantity:
- >0 represents an unknown, but non-negligible, quantity greater than zero.
- A > character prefixing a number means that this is a sum or a product that includes a >0 number, e.g. 3.2 + >0 = >3.2
The table below shows the standard reporting units of NTMCalc.
|Fuel consumption||l, m3,kg|
The outputs above are never reported per kilometre or tonne-kilometre. There are two reasons for this:
- Emission and energy use levels are not always linear to the distance travelled. The relationships are linear for road, rail and rail transport modes, but this not true for air where take-off and landing is much more energy demanding than crusing. So if the emissions of an air transport would be recalculated and reported per kilometre or tonne-kilometer, the numbers would, counter-intuitively, only be valid for the originally specified distance.
- It goes for any output that it is valid, and only valid, for the exact combination of parameter values specified in the Transport Activity Specification Wizard (road type, fuel type, cargo load factor, etc), and for this reason it cannot be generally applied to any vehicle of the same type. Reporting per kilometre or tonne-kilometer can lead to a misconception about this important condition.
- The decimal point is denoted with a period, e.g. 1.234
- Scientific notation is used to write numbers that are too big or too small to be conveniently written in decimal form. In scientific notation all numbers are written in the form of a*10b (a times ten raised to the power of b). Because superscripted exponents cannot always be conveniently displayed, the letter E is used to represent times ten raised to the power of, e.g. 2*103 is written as 2E3. Examples:
- 1.2E3 is 1200 with two significant figures
- 1.200E3 is 1200 with four significant figures
- 1.23E0 is 1.23
- 1.23E-1 is 0.123
- 1.23E-3 is 0.00123
Rounding of measurements to significant figures
Most numerical data handled by the system (user input, database values, etc) represent approximate measurements and it is important that reported numbers do not appear to be more accurate than they really are. This will require the system to implement a proper set of rules for rounding, and for this purpose the concept of significant figures has been adopted. In short this means that numbers are rounded to the last figure that has accuracy. If distance would be measured with a measure tape used for carpentry, any measurement smaller than a millimeter would be of very low accuracy due to the precision of the device, and followingly a measurement of 4.5678 meters would be rounded to 4.568 meters (the fourth digit being the last digit of accuracy). Examples:
- 1.234 rounded to two significant figures is 1.2
- 7.5678 rounded to one significant figure is 8
- 1234 rounded to two significant figures is 1200 or 12E2 depending on whether trailing zeroes are considered to be significant or not. In NTMCalc this differs between input and output data, please review the sections below for more detail on this.
Addition and subtraction with significant figures
When adding and/or subtracting measurements with different degrees of accuracy and precision, the accuracy of the final answer can be no greater than the least accurate measurement. This principle can be translated into a simple rule: When measurements are added or subtracted, the answer can contain no more decimal places than the least accurate measurement. Example: 3.0 + 1.025 = 4.0
Multiplication and division with significant figures
The same principle governs the use of significant figures in multiplication and division: the final result can be no more accurate than the least accurate measurement. In this case, however, we count the significant figures in each measurement, not the number of decimal places: When measurements are multiplied or divided, the answer can contain no more significant figures than the least accurate measurement. Example: 2 * 3.3 = 7