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the intended carbon savings from energy efficiency measures are often not realised in practice, because people spend the money they save on other goods or services that require an energy input. This is the so-called ‘rebound effect.’
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http://energysavingtrust.wordpress.com/2012/02/22/reduce-rebound-reoffend
Presume this has some relevance to cycling/driving.
Though obviously there are more good reasons for cycling (especially in urban areas) than energy/carbon.