In a different thread, I found https://www.fueleconomy.gov/feg/Find.do?action=sbs&id=40076 as a useful way of looking at CO2. That's got the Honda Fit as that's the one that was in discussion previously. Its a 33mpg car and the 'energy and environment' tab puts it at 4.4 tons/year. I've got a 2009 Honda Insight.

> Fuel cost estimates assume national average fuel prices and assume you drive 15,000 miles each year, 45% under highway driving conditions (steady speeds with little or no stopping) and 55% in city driving (low speeds with lots of stopping).

Noting that I'm not the typical home worker, but I went from an average of 600 miles/month (7200 miles/year) to 30 miles/month over the past year and a half. This took my carbon footprint for driving from 1.7 T/y to 0.1 T/y.

The flip side of this number is (for me) that I went from heating the house only a few hours a day in the winter to heating or cooling one room to comfortable. I don't have good numbers on my electrical footprint change. This would again be different with different life circumstances (number of other people in the house, size of house / apartment, etc...)