The are a number of myths surrounding cars and driving, from the advice to heat up your engine in the winter to the idea that red cars are more likely to get pulled over. The rule against letting your engine run while pumping gas, however, is very much rooted in fact. Here's why you should never leave your car on when filling up its gas tank.

Gasoline is extremely flammable, which is why gas stations prohibit smoking and having any sort of open flame around their pumps. It's also why stations ask customers to shut off their engines before refueling. Even though cars are designed for safety, the unique mix of factors at gas pumps can create hazardous conditions.

In rare cases, the heat and electricity produced by your vehicle can be enough to ignite liquid gas that splashes out of the pump or gas vapors in the air. Though it doesn't happen often, this has occurred in the past, according to the Petroleum Equipment Institute [PDF].

In the colder months, it may be tempting to leave your heat on at the gas pump, or wait in the car while you wait for the tank to fill up, but the safest thing to do any time of year is to stand by the pump until you screw the gas cap back on. Even when your engine is off, normal static electricity caused by movement can be enough to ignite gas station fumes. Re-entering and exiting your vehicle can cause static to build up, especially in the winter when the air is drier and you're wearing more layers of fabric. If you want to be safe, swipe your bare hands against the metal side your car door to ground yourself before pumping gas.

For more ways to be a smarter motorist, check out these road safety tips.