ETA Travel Advisor Assumptions

This page outlines the values assumed in the ETA Travel Advisor for emissions of CO2, NOx and Dust, plus Calories consumed.

By default, emissions are expressed relative to distance, by mode. For public transport, mode is sub-divided by vehicle category (for example bus, coach, national rail, light rail). Where no mode-specific information is available, the average of bus and rail is assumed. Car (and taxi) are expressed here per vehicle, but automatically factored by group size in the App to show analysis by passenger. Other modes/vehicles are shown by passenger kilometre (“pkm”).

Carbon Dioxide

Carbon Dioxide emissions are taken from the UK Department for Environment, Food, and Rural Affairs’ Greenhouse Gas Conversion Factor Repository, 2015. Carbon Dioxide equivalent values are used.

• Bicycle and Walking: 0 kg/km. App assumption. The inclusion of food consumed by the person would be contentious, since many people already consume more than they need to live, and thus many (shorter) journeys by bicycle or foot represent a marginal use of CO2 already generated.
• Bus: 0.1003 kg/km.
• Car (including taxi): 0.1823 kg/km. Assumes diesel.
• Coach (intercity): 0.0293 kg/pkm.
• Ferry: 0.116 kg/pkm.
• Light Rail (metro, subway, tram and trolleybus): 0.0546 kg/pkm.
• Rail (generic, heavy, commuter): 0.045 kg/pkm.
• High Speed Rail: 0.012 kg/pkm. Assumes international rail.

Good (100%, happy score) value for Carbon Dioxide is 0 kg/pkm. Bad (0%, unhappy score) is 0.18 kg/pkm (single occupancy car).

Dust (PM10)

Source for road-based modes is the UK National Atmospheric Emissions Inventory (Fleet Weighted Road Transport Emission Factor 2011). Rail-like modes are sourced from the AEA Energy & Environment “Tool for calculation of CO2 emissions from organisations”, 2010. Dust is particularly dependant on fuel and age of vehicle. Diesel emissions can be 20 times higher than petrol. Euro-3 standard engines (common since 2001) produce 10 times more Dust than Euro-5 (2011).

• Bus: 0.0079 g/pkm. Base 0.081 g/km divided by a 20% load factor for 51 seats (consistent with Carbon Dioxide calculation).
• Car (including taxi): 0.011 g/km. Unweighted average of urban, rural and motorway driving for all car type “hot exhaust and cold start emission factors” (which attempt to account for the initial starting of the vehicle when the exhaust is cold).
• Coach (intercity): 0.0015 g/pkm. Base 0.081 g/km divided by a 60% load factor for 91 seats (consistent with Carbon Dioxide calculation).
• Light Rail (metro, subway, tram and trolleybus): 0.00000396 g/pkm.
• Rail (generic, heavy, commuter, high speed): 0.00923 g/pkm.

Good (100%, happy score) value for Dust is 0 kg/pkm. Bad (0%, unhappy score) is 0.011 g/pkm (single occupancy car).

Oxides of Nitrogen

Source for road-based modes is the UK National Atmospheric Emissions Inventory (Fleet Weighted Road Transport Emission Factor 2011). Rail-like modes are sourced from the AEA Energy & Environment “Tool for calculation of CO2 emissions from organisations”, 2010. Like dust, NOx varies with fuel and age, although the differences are not as great as for dust.

• Bus: 0.64 g/pkm. Base 6.5 g/km divided by a 20% load factor for 51 seats (consistent with Carbon Dioxide calculation).
• Car (including taxi): 0.38 g/km. Unweighted average of urban, rural and motorway driving for all car type “hot exhaust and cold start emission factors” (which attempt to account for the initial starting of the vehicle when the exhaust is cold).
• Coach (intercity): 0.12 g/pkm. Base 6.5 g/km divided by a 60% load factor for 91 seats (consistent with Carbon Dioxide calculation).
• Light Rail (metro, subway, tram and trolleybus): 0.000136 g/pkm.
• Rail (generic, heavy, commuter): 0.399 g/pkm.

Good (100%, happy score) value for Dust is 0 kg/pkm. Bad (0%, unhappy score) is 0.64 g/pkm (bus).

Calories

Assuming an average individual weight of 77 kilograms, based on BUPA, walking at an average speed of 3 miles per hour, or bicycling under 10 miles per hour, uses 5.1 kcals per minute, 0.085 per second. Car and public transport modes are assumed to expend zero calories.

Good (100%, happy score) value for Calories is 0.085 kcal/s (cycling and walking). Bad (0%, unhappy score) is 0 (passive modes).

Money

Driving costs use the HM Treasury value of £0.45 per mile. This covers the total cost of driving, not just the fuel cost.