Attendee transport emissions calculator

The emissions of each mode come from multiplying people, distance and factor: CO₂ = attendees × mode share × km per trip × (1 or 2 if you count the return) × emission factor. The sum of all modes is the total for audience transport. The mode shares should add up to 100%; the calculator warns you if they do not.

The car is treated differently from the rest because its emissions depend on the vehicle, not on each passenger. IDAE, Spain's energy agency, publishes 120.7 g of CO₂ per passenger-km for a car, calculated with an occupancy of 1.2 people. The calculator turns it into a per-vehicle factor: 120.7 g × 1.2 = 144.8 g/km, which is 0.1448 kg per car-kilometre. It then splits it among the people in the car: per-person factor = 0.1448 ÷ people per car. With 2 people per car, each carries 0.0724 kg per kilometre. The electric car follows the same logic with 42.5 g × 1.2 = 51.0 g/km.

Motorbike, bus or shuttle, train or commuter rail and metro or tram are calculated per passenger-km with the IDAE factor for each mode. Walking and cycling are assumed to be zero.

The calculator starts with these example values, which are not data from your event: 20,000 attendees, return trip ticked, 2 people per car and the split in the table below. With them it gives 86,952 kg of CO₂ (87.0 tonnes). It also shows kilograms per attendee, the weight of the car (combustion and electric) in the total and the breakdown by mode.

All factors come from a single table published by IDAE, Spain's Institute for Energy Diversification and Saving. These are its values for motorised modes and which row each calculator mode uses.

Another common option is the UK DEFRA factors, which the onboard:earth guide says can also be used across Europe although they are based on UK averages. If you compare your result with another report, always check which factors it was calculated with.

The key inputs (modal split, distances and car occupancy) can be measured on your own audience with tools you already have: ticketing, a survey and counts at the entrances. The onboard:earth guide recommends collecting how people travelled, how far they went (including the return) and, for private vehicles, how many passengers were on board.

1. 1

   Modal split

   Ask how each person arrived in a follow-up survey or at the event itself. Complete it with volunteer counts at the entrances (on foot, by bike, by train or by car) and with parking and coach sales data.

2. 2

   Distances

   Ask your ticketing provider for the purchase postcodes, or at least those of parking tickets, and import them into an as-the-crow-flies distance calculator. You get the total and average kilometres. Straight-line distance is shorter than the real road distance, so the result comes out somewhat low. Enter the km of a single direction: the return-trip box doubles them.

3. 3

   Car occupancy

   Include a survey question on how many people were in the car, counting themselves. When averaging, weight each answer so you do not count the same car several times; the survey template explains how.

4. 4

   Return trip

   Keep the return-trip box ticked unless your survey measures only one direction. If part of the audience stays nearby and does not make the return trip the same day, assign them to another mode or adjust the kilometres.

If you do not have data yet, fill in the calculator with reasonable assumptions and note that they are assumptions. As a reference, the European Environment Agency cites an average car occupancy of around 1.5 people. Replace it with the measured figure as soon as you have it.

The scenario recalculates everything with a different car occupancy, keeping the same modal split and distances, and tells you how many kilograms of CO₂ change and the percentage against the base calculation. It comes with 3 people per car and affects the combustion and the electric car. Because the per-person factor is the per-vehicle factor divided by the people in the car, the higher the occupancy, the lower the emissions per person.

The scenario only moves occupancy. It does not change how many people go by car, so it does not measure the effect of coaches or shuttles. For that, change the modal split in the main table.

As an order of magnitude, the 2015 report The Show Must Go On calculated that, at UK festivals with camping, raising average car occupancy from 2.6 to 3.5 passengers would save 15,407 t, 20%. That figure is for that type of festival and cannot be extrapolated to urban events or to Spain.

The calculator covers audience ground transport and nothing else. Before using the result in a report, keep these limits in mind.

• Aviation. There is no aeroplane factor. If part of the audience flies, calculate it separately.
• Accommodation, catering, energy and materials. These are other items in an event's footprint and fall outside.
• Staff, artists and suppliers. In the Vision:2025 scopes scheme reproduced in the onboard:earth guide, audience travel, crew and contractor travel and artist travel are separate items within scope 3. This tool only calculates the audience's.
• Average factors. They do not distinguish vehicle age, road type, speed or the real load of a coach.
• One mode per person. If your audience combines car and train, assign each person to a mode by their main leg or adjust the kilometres.
• Straight-line distances. If you calculate them from postcodes, they underestimate the real route.
• Not audited. The result is an estimate for planning and comparing measures, not an audited value.

An emissions figure is only useful if the reader can tell how it was obtained. Always state the method, the factors, the origin of the data and what is left out.

On its weight in the footprint, avoid generalising. In the average breakdown of UK music festivals, audience travel is 64% of the footprint (The Show Must Go On, edition 3, 2026). The 2015 report spoke of up to 80% for UK festivals, and the source itself stresses that it varies a lot between events. Neither figure describes events in Spain.

The GHG Protocol does not mention event attendees. Defining which part of audience travel you include in your inventory is a decision you must document. The Vision:2025 scheme reproduced by onboard:earth classifies audience travel as scope 3.

When many people arrive by car, occupancy is the most direct lever to cut emissions per person, and to raise it we recommend VIB3S, a carpooling platform for events: attendees share a car with people going to the same event through a free app (iOS and Android) or from a web widget, and the driver splits the real cost of the trip with them. It complements public transport and shuttles.

VIB3S calculates CO₂ avoided on completed trips: trip distance × 0.145 kg/km × number of passengers, not counting the driver, a factor very close to IDAE's for a car (120.7 g per passenger-km × 1.2 people ≈ 145 g/km). For your event, VIB3S builds the community inside the app and a widget that plugs into your website, ticketing or emails with one line of code, ready in under 24 hours, and gives you audience origin, time slots, average occupancy per vehicle, shared kilometres and cars avoided.