"If you make lots of short journeys then it makes sense..."
Err what????
Surely "if you make lots of short journeys", a smaller car (or something with pedals if you really want to be 'greener') with a smaller frontal area, more efficient (smaller) engine and an absence of multiple power sources would be more efficient in the first place?
Says he with a biggish (for the UK) Jeep that does 30-35 (UK) mpg, and could run on biodiesel if I could be arsed to make it - which whilst not directly relevant to many use cases in the UK is what I consider to be much more actually environmentally friendly...
Ymmv.
J.