Cindi, if that turtle was a soft shell turtle it was harmless, but the hiss a turtle makes is alarming. The hiss is actually the air being forced out of their lungs by their bodies being compressed as they move in their shell. Most turtles can spring their legs out quickly for one quick jump, but that's it.
The exception is snapping turtles. Their bottom shell is much smaller than that of most turtles, allowing them much more movement. They can run and jump, and they're fast! Very fast!! For short bursts that is.
Around here, in upstate New York, in early summer, the female snappers come out of ponds, lakes and streams to lay their eggs in sand and gravel. They're big turtles, they can be one to two feet long. They often cross roads, and as you notice, people will run them over. My wife and I keep shovels in our trucks all year. During the winter, we use them in case we get stuck in a snowdrift. During the summer, we use them to push or pull female snapping turtles out of harm's way. You gotta be careful with them, if you get too close theyll strike at you like a snake. But they don't deserve to be squashed by cars.
Interestingly, though, when they're in water, they're pretty harmless. I've even stepped on them wadding in our creek, thought I was standing on a rock, when the rock suddenly started moving! /forums/images/graemlins/blush.gif The turtle could've taken off several of my toes, but they just move away. They're not scared in water, because they're graceful swimmers, but on land they're clummsy and defensive. Can't blame them for that!