A car needs fuel to get running fuel. Thus, no driver in his or her right mind would drive with no or little fuel left. You might get stuck in the middle of the road, and this isn't one of the situations that a driver would want to run into. However, you might just get stuck on the road with an empty tank if you continue ignoring the illuminated gas light on the dashboard.
The gas light – also known as fuel light, low fuel indicator, fuel warning light – doesn’t really turn on when the fuel tank is already empty. Instead, the gas light turns on when fuel in the tank has reached an incredibly low level. Typically, the gas light turns on when there is only between one gallon and two gallons of fuel left in the tank. It totally depends on the manufacturer on how much fuel really remains in the tank.
Nonetheless, the remaining distance that a car can travel after the gas light turns on is totally dependent on its fuel economy rating. For example, if the gas light turns on when only two gallons are left on the tank and your car’s fuel economy rating is around 25 mpg, then you only have around 50 miles to travel before the tank totally empties.
Essentially, the gas light, when turns on, tells the driver that the car’s fuel level is in a dangerous level and it is now time to refuel. Because the fuel tank isn't really totally empty, you have enough fuel to drive off to the nearest gas station. When the gas light turns on, it is also warning you not to wait until the fuel tank empties, as it might lead to a number of dire consequences.