The most environmentally friendly car: Your Car

Leo Hickman has initiated a discussion at the Guardian regarding a Norwegian study indicating the environmental benefits of electric cars can be absent - in some situations.
The findings reminded me of a controversial 2007 study,  "Dust to Dust: The Energy Cost of New Vehicles From Concept to Disposal ."  Both studies have catchy hooks, but I think both also note the environmental impact of your car depends on the utilization of your car.  The message I recall taking from the hated "Dust to Dust" study was that people drove big vehicles a lot, but the claim was small hybrids seldom got driven - so the LCA was based on one car used for 100,000km vs. a bigger one vs 400,000km.  
This new study states that if you are only going to drive a car for 100,000km the electric car is no better than a small efficient traditional vehicle.  It's hard for me to picture how a car requiring tethering to a supply source every 100-150 km is likely to get a lot over 100,000km, so it seems like a valid criticism.
But ... if you are in that situation it is likely urban, and immediate airshed quality is likely better with electric.
Similarly, for global warming it is almost certain that putting more mileage on your car is more AGW friendly than any new vehicle. and a good mechanic far greener than an electric car.
Again, this may not be true of the impact on the immediate airshed.   I have no particular air quality concerns where I live - so it's a tank of premium gas with a bottle  of 'Guaranteed to Pass' added to burn off for a couple of hours before getting an emissions test on old clunkers when the engine is hot.
It's the earth friendly thing to do.

Summary of Comparative Environmental Life Cycle Assessment of Conventional and Electric Vehicles - Hawkins - 2012 - Journal of Industrial Ecology - Wiley Online Library:

Electric vehicles (EVs) coupled with low-carbon electricity sources offer the potential for reducing greenhouse gas emissions and exposure to tailpipe emissions from personal transportation. In considering these benefits, it is important to address concerns of problem-shifting. In addition, while many studies have focused on the use phase in comparing transportation options, vehicle production is also significant when comparing conventional and EVs. We develop and provide a transparent life cycle inventory of conventional and electric vehicles and apply our inventory to assess conventional and EVs over a range of impact categories. We find that EVs powered by the present European electricity mix offer a 10% to 24% decrease in global warming potential (GWP) relative to conventional diesel or gasoline vehicles assuming lifetimes of 150,000 km. However, EVs exhibit the potential for significant increases in human toxicity, freshwater eco-toxicity, freshwater eutrophication, and metal depletion impacts, largely emanating from the vehicle supply chain. Results are sensitive to assumptions regarding electricity source, use phase energy consumption, vehicle lifetime, and battery replacement schedules. Because production impacts are more significant for EVs than conventional vehicles, assuming a vehicle lifetime of 200,000 km exaggerates the GWP benefits of EVs to 27% to 29% relative to gasoline vehicles or 17% to 20% relative to diesel. An assumption of 100,000 km decreases the benefit of EVs to 9% to 14% with respect to gasoline vehicles and results in impacts indistinguishable from those of a diesel vehicle. Improving the environmental profile of EVs requires engagement around reducing vehicle production supply chain impacts and promoting clean electricity sources in decision making regarding electricity infrastructure.

The study can be read here: