Crocodiles and alligators can run at speeds up to 18kph (11mph) for very short distances. They do this by by trotting, galloping and bounding. Alligators only trot at what seems like a quick-paced walk. Crocodiles also trot, but as they gain speed, they switch to galloping and bounding.
While trotting, a crocodile or alligator lifts and places diagonally opposite legs almost simultaneously. For example, the front right and rear left legs are lifted almost simultaneously and placed on the ground. The process is repeated with the alternate left rear and right front legs.
At a gallop, a crocodile comes down on one back leg, then, almost simultaneously, on the diagonally opposite front leg and the other back leg, and finally on the other front leg.
When bounding, a crocodile moves by lifting the front of its body off the ground and throwing its front limbs out and forward as the hind limbs thrust the body forward. It then lands on its front limbs first and repeats the process.
So, if you see a crocodilian trotting at full speed, it's an alligator. But if it's galloping and bounding then it's a crocodile.
A galloping crocodile is a terrifying sight indeed. But, although a crocodile can run faster than a human, it can do so for only 20-30 metres before its tires out. So as long as you keep your nerve and run for your life, you will probably outrun the crocodile. Besides, crocodiles don't usually chase prey on land. Instead, it is probably running away from a potential threat or trying to reach prey in the water quickly.