[greenyoda]

It's not just a question of thermodynamic efficiency. Cars have emission control systems (catalytic converters, etc.) that mitigate some of the pollutants, and perhaps most importantly, use a much cleaner fuel (the heavy fuel oil burned in power plants produces soot, sulfur compounds, etc. which the more highly refined hydrocarbons in gasoline do not).

[sqeaky]

I don't think he was talking about thermodynamic efficiency. But filtering efficiency. Filtering one big power plant is easier than filtering many independently owned cars. Also the power plants filter is stationary and the cars filters must move.

[mcv]

Cars are not as dirty as they used to be, but the internal combustion engine is still incredibly inefficient, and has only a narrow band where it runs at optimal efficiency.

It is of course possible to make power plants even dirtier and less efficient, but it's also possible to make them cleaner and more efficient, which is of course what we should be doing.