Years ago when metal tanks were common, fuel was of lower quality, and other factors, it was not uncommon for the car fuel line to freeze up. Today this is not so common, but not impossible. However, freezing is prevented by making sure that the gas level is not below half a tank. When your gas tank has more air, the moisture in the air can freeze and leave ice flakes which then clogs the line. This usually happens when the car is sitting for a few hours in the cold, but the fuel line can also freeze while you are driving if the conditions are cold enough.