My city is laid out in 1 mile grids The one mile square I live in has 4 lanes on all 4 sides of it. The 3 year old traffic count I found on line gives each side of the square a value, combined its almost 75,000 vehicles, which in this case would also be about 75,000 miles driven.
The national fleet (the whole mix of cars and light trucks) now gets at best 20 mpg. Now I'll spare the math here but it works out to 3,750 gallons burned every day on the perimeter of my square just for the drive. At each of the corners is a traffic light, about 1/3 of the cars get caught at one end or another of this mile and set for about 3 minutes, so thats 75,000 minutes burning 1/4 gallon per hour at idle, for another 312.5 gallons just to go nowhere.
That's 4,063.5 gallons up in smoke every day, and close enough to be a concern. (todays price $3 gal). Tomorrow I will find out how much CO2 that was.