That's a very good question, and you show a lot of promise for asking it.
You will find "horizontal highway hostesses" all over the place, and in most cases they're harmless. Of course, as with anything, there are exceptions. Some of them are drug addicts, and will do anything for that next fix. Some of them are too lazy to get a real job, and some of them are acting out of desperation, i.e. the economy and kids to feed.
No matter what story they give you, avoid all of them. Think about it. Look around you and check out some of the drivers. Pretty scummy, right? Do you want to take a chance on having relations with someone that was with one of them and maybe get crabs, scabies, vd or the ultimate, AIDS?
Here's something else to be aware of. Nice looking lady, legs up to there, cleavage out to here, approaches you and says she needs a ride somewhere and will do anything for it. Chances are she already has. On top of that, you really don't need to fall asleep with someone you just met and don't know unless you want to wake up with your money and valuables gone or not wake up at all. There are too many cases to count of horny truckers being rolled or killed by these women or their boyfriends.
If you really need to do something about blue balls, get a run through Nevada and stop at one of the legal brothels out there. They are regulated, taxed, and most of all clean. Either that or go home and grab your girlfriend wife or whatever. And if you're married, you should get a run that keeps you close to home so you don't miss each other too much.
Other than all that which I have written, just keep to yourself and be aware of the usual scam artists in this world and don't let anyone in the truck that you do not know. Some of them carry guns and knives.
Be safe and good luck to you. Some of us older guys are counting on you to keep things moving after we're gone. It can be a good life, and you'll get to see country that most people dream about.
Oh, and carry a spare fire extinguisher with you. They're pretty cheap at Wal-Mart, and the look on a girls face just before you shoot her of the running boards is priceless!