In the testing literature, the term load testing is usually defined as the process of exercising the system under test by feeding it the largest tasks it can operate with. Load testing is sometimes called volume testing, or longevity/endurance testing.
Keep your taste buds awake, drink an energy drink. This may raise your level of alertness for a reasonable amount of driving time. Suck or munch on an apple, orange, or even a lemon to keep taste buds awake. The more tangy the food item the better. (Pull over somewhere safe before eating anything that you can't just pop in your mouth, however.
Stimulate your senses. The easiest way to stay awake is to stimulate your senses. There are a number of things you can do to make sure your ears, eyes, and even your nose are alert and active. The more parts of your body that are alert, the less likely it will be that you will fall asleep.