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.

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.

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.

Fuel Costs

Average fuel cost (for all fuels) is taken at £1.1091 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.

Carbon Dioxide Emissions

The average car will emit 204.6 grams of carbon dioixide (CO2) per kilometre.

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.

Hot Air Balloons

One hot air balloon is equivalent to 1.8 tonnes of CO2.

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.

Passenger trips and savings

All savings calculations assume that car-sharers would otherwise drive alone. To be able to calculate the number of passenger trips and mileage saved through sharing, Liftshare have to make an assumption around which member/s of a BUDi team would drive. Firstly we look at the size of the BUDi team, which impacts the number of people that will be required to drive (we assume that a car can hold 5 individuals). Once we have this, a number of factors are used to rank who would most likely be the driver/s. Those journeys that have been registered as offering or offering & seeking a lift are ranked as most likely to drive. We then further rank members by how often members travel and how far. With drivers selected it then allows Liftshare to estimate the savings that occur through other BUDi team members travelling as passengers. Liftshare are seeking feedback from members upon how often they typically share their journeys. For those shared journeys where no feedback is received, Liftshare will use the frequency of the registered journey as a guide. If a journey was registered as a return trip made on Mondays and Tuesdays – this would be 4 trips. For journeys where members have confirmed their typical level of sharing as less than once per week we assume that this is a return journey that occurs once a month. The number of weekly shared trips we assume is therefore 0.5 (one trip a month is 0.25 trips per week, which is doubled as it is a return journey).

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.