You name me a car capable of getting 40 mpg, and I'll show you how to get 13 (actually 17) mpg out of it.
The car I did it with is my wife's '06 AT Hyundai Elantra. We drove at night, had to run the heater and lights, and didn't hit many stoplights on green. We also had to drive the Strip on a weekend, with its stop and go traffic. Even FASing at lights, I could only get 17 mpg that night.
When I lived in Alaska, I could only expect 5 mpg in the winter with my 4X4 Scout. Winter driving kills fuel economy.
I actually averaged >41 mpg over ~1000 miles on that trip. It just took all day to overcome the effects of that first 13 miles at 17 mpg. When you're doing short commutes every day, you never overcome the cold starts.