[maxerickson]

The recent Ford F-150s with aluminum bodies were huge news. The frame is still steel.

Personal vehicles are mostly made of steel.

[timthelion]

And steel actually produces even more CO2 to cast. Carbon steel, melting point 1500C vs aluminium, just 600C. http://www.engineeringtoolbox.com/melting-temperature-metals...

[maxerickson]

The specific heat is also important, not just temperature.

You also have to look at refining (it takes a huge amount of energy to produce raw aluminum) and recycling (steel is really, really recyclable).

[timthelion]

Well they both take more energy to cast than my average bowl of mashed potatoes and peas that's for sure!