Assumptions and references used in Liftshare statistics

Miles per gallon

For a car of unknown fuel, the average number of miles per gallon is 33.6.
source: www.defra.gov.uk/publications/files/pb13625-emission-factor-methodology-paper-110905.pdf

Number of Working Days Per Annum

232 - This is assuming that you work a 5 day week and receive the minimum holiday entitlement of 28 days annual leave (including 8 bank holidays). This was updated in April 2009 along with the changes to the minimum holiday requirement.
source: www.direct.gov.uk/en/Employment/Employees/Timeoffandholidays/DG_10029788

Journey Distance

To calculate ‘actual’ journey distance we take the distance that the ‘crow flies’ (i.e. in a straight line) and multiply by 1.25.
source: www.transportdirect.info/Web2/staticnoprint.aspx?id=_web2_help_helpcarbon

Fuel Costs

Average fuel cost (for all fuels) is taken at £1.3165 per litre. These figures are updated fortnightly. We do not take into account past changes in fuel costs. All of our calculations use the current fuel price.
source: www.petrolprices.com 

Carbon Dioxide Emissions

The average car will emit 204.6 grams of carbon dioixide (CO2) per kilometre.
source: www.defra.gov.uk/publications/files/pb13625-emission-factor-methodology-paper-110905.pdf

Nitrogen Oxides Emissions

23 mg of Nitrogen Oxides are emitted per vehicle kilometre for an average petrol car with catalyst.
source: www.lordgrey.org.uk/~f014/usefulresources/aric/Resources/Fact_Sheets/Key_Stage_4/Air_Pollution/26.html

Particulate Matter Emissions

Particulate Matter emitted is negligible in petrol cars, but the population weighted average emissions from cars is 11 mg per vehicle mile. Diesel cars however, emit a significant amount (up to 10 times more PM).
source: www.epa.gov/otaq/emission-factors-research/420r08010.pdf, p.23.

Carbon Monoxide Emissions

42 mg of carbon monoxide is emitted per vehicle kilometre, for an average petrol car with catalyst.
source: www.lordgrey.org.uk/~f014/usefulresources/aric/Resources/Fact_Sheets/Key_Stage_4/Air_Pollution/26.html

Hydrocarbons

19 mg of Hydrocarbons are emitted per vehicle kilometre for an average petrol car with catalyst.
source: www.lordgrey.org.uk/~f014/usefulresources/aric/Resources/Fact_Sheets/Key_Stage_4/Air_Pollution/26.html

Average Occupancy of Shared Vehicles

2.5 people.
source: 2008 survey of liftshare members

Wear and Tear Costs

Average wear and tear cost works out at 9.02p per mile. This figure is taken from the AA’s 2012 document on ‘Running Costs’ and is based on an average purchase price for a new car of £33,500.
source: www.theaa.com/resources/Documents/pdf/motoring-advice/running-costs/petrol2012.pdf

Distance Around the Earth

The circumference of the earth round the equator is 40,075.02km or 24901.46 miles.
source: David R. Lide, "Handbook of Chemistry and Physics", 81st edition, (CRC: 2000)

Hot Air Balloons

One hot air balloon is equivalent to 1.8 tonnes of CO2.
source: http://www.uea.ac.uk/lcic/cred

Carbon Dioxide Absorption

We assume that a tree will sequester atmospheric carbon dioxide at an average of 50 pounds of carbon dioxide per tree per year. This is the equivalent to 22.6796185 kilograms a year.
source: www.plant-trees.org/resources/Calculating CO2 Sequestration by Trees.pdf

Other Assumptions

All of our savings calculations assume that car-sharers would otherwise drive alone. Occasional/Shift journeys are counted as one-off return journeys.