There’s a great post at The Oil Drum by Jeff Radtke that gives people a good way of evaluating the resource uses in their cars. Now you don’t actually have to do this to figure out that light cars are better than heavy ones – the results aren’t that difficult. But if you think it is fun to figure out smaller distinctions, it is worth doing.
This type of analysis is useful because it is easy to factor in conversion efficiencies and payload versus tare weight. Rather than use motor output power, one can use the thermal power theoretically available in the flowing fuel. EROI may be factored in, as well as GHG emissions. Analysis may be completed at the level of individual trips, vehicles, or an entire system with resource extraction, infrastructure development, manufacturing and direct fuel use.
Kinetic energy divided by required power is considered a residence time for the input energy in the utilized form. This model may provide an intuitive understanding of energy use. Residence time for anything in a container is the quantity residing divided by the flow rate. This is as true for a vehicle containing kinetic energy as it is for a mountain lake holding melted glacier, or the CO2 present in our atmosphere
I do have a bit of a quibble with Radtke’s assumption that one will continue, in the longer term, to be the standard number of car passengers – and indeed, if you want to green your ride, the single best way to green your ride is probably not to buy a brand new car, but to put more behinds in your car when you do drive. Yes, yes, I know the carpool is impossibly retro, but hey, retro is cool.