The technology car stock model based on work presented in   [Daly, H. Ó Gallachóir, B.P., 2011. “Modelling private car energy demand using a technological car stock model.” Transportation Research Part D: Transport and Environment. 16(2), 93-101] and Daly, H., Ó Gallachóir, B.P., 2011. “Modelling Future Private Car Energy Demand in Ireland.” Energy Policy, 2011. 39, 7815-7824

Ireland’s yearly vehicle licensing data from 2000 to 2008 is used to generate a technological stock profile by disaggregating the cars by fuel type, by engine size bands (0–900 cc, 901–1000 cc, etc.) and by vintage. Age, engine capacity and fuel type are strong determinants of a car’s efficiency. The engine size profile of a fleet is an important technological parameter, as a car’s cc is directly proportional to its power output. Specific fuel consumption then depends on the engine’s efficiency, which depends on individual vehicle technology. Age is also influential: with average new-car energy intensity decreasing over time and with ageing cars’ intensity increasing over their lifespan, a younger fleet with a higher turnover rate will be more efficient. Also, due to the different technologies behind diesel and petrol vehicles and the higher energy content of diesel, the fuel mix is an important parameter in the fleet’s intensity.

It should be noted that measuring the stock of in-use cars can be difficult because of the discrepancies that typically exist between the number of cars registered in a year, the number of cars taxed at any particular time, and the average number of cars in-use. The car stock model is created from databases including the fuel type, engine capacity and year of manufacture of cars taxed for each year between 2000 and 2008. If data on the age profile of the fleet are not collected, it may be modelled using historical scrappage rates. If the retirement rate of the fleet is known, the age profile of the fleet can be derived from sales data.

For more information on this model please contact Dr Brian O Gallachoir.

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