The development of a CO₂ calculator is a very useful tool for mobilising public transport customers around climate change issues and the impacts of each trip. This tool enables public transport operators to share information about emissions linked to the services they provide, and to compare these to emissions from other transport modes.

Scope

The carbon emissions of a transport service shall include both vehicle operational processes and energy operational processes, which occur during the operational phase of the transport service. The vehicle operational processes shall include operation of all on-board vehicle systems including both propulsion and ancillary services. The energy operational processes should at least include:

• for fuels: extraction, refining, transformation, transport and distribution of energy at all steps of the production of the fuel used
• for electricity: extraction and transport of primary energy, transformation, power generation.

The assessment shall not include the carbon emissions linked to:

• leakage of refrigerant gases
• external movement devices like elevators and moving walkways
• processes involved in the transport services, like operation of buildings, staff commuting and business trips, computer systems, etc.
• the construction, maintenance and scrapping of vehicles
• construction, service, maintenance and dismantling of transport infrastructures used by vehicles
• non-operational energy processes, such as the production or construction of extraction equipment, transport and distribution systems, power production plants, etc. as well as their recycling and scrapping.

If there is any official regulation, the included or excluded emissions must be in line with the requirements of the country. For instance, in France currently, the regulation calls for communication about carbon dioxide (CO₂).

Calculation

To monitor the emission of a trip, the company must split the trip into different legs (segments). The following data must be known:

• the breakdown of the route into segments and modes (walking, biking, car, bus, tram, etc.)
• a distance estimation for each segment
• a carbon emissions factor value for a reference distance of each segment.

The first two points are directly linked to the route planner of the operator. Each network has its own methodology to evaluate the distance on each segment. It can be:

• real distances
• ‘as the crow flies’ distances
• ‘as the crow flies’ distances multiplied by a correction factor.

To be able to measure CO₂ emissions, the trip calculator has to have access to the distance of the segments for the defined trip. The route planner must be built to allow the trip calculator to include the distance on each segment.

The third point related to the CO₂ emissions factor is derived from performance indicators based on a carbon balancing approach (see the performance indicators section). The total emissions of the trip will be the sum of the emissions of each trip segment. The emission factors have to be updated according to the development of the performance indicators.

To offer users a good understanding of the emissions caused by their travel and to allow them to compare these emissions to those from other modes of transport, the trip calculator must clearly present on the website the methodology that has been used and the chosen emission factors.