I've run into many snakes - all of the North American poisonous ones - in my life. When I was living in Texas. On only one occasion did I ever think a snake was aggressive. That was a water moccasin (a.k.a. "cottonmouth"). He did not "attack" or anything like that, but he stood his ground and wouldn't move out of the way. I've run into many water moccasins and it was only this particular one who appeared belligerent. Most will hightail it towards the water. Don't confuse them running for the water with an attack if you happen to be standing between them and the water. They'll just fly right past you. Every other snake I've run into, including many many rattlers, were more than happy to run away when given the opening to do so.

Walk down the middle of the trail. Not to the sides.