Random encounters? I've never run into them, maybe because I fast travel almost everywere because it's borring to walk everywere, nothing to see in the FO games I find...
what kind of random encounters?
All kinds of random encounters, and most outside enemies repsawn, as mentioned. so theres plenty of gun fights out there. How far are you in the main quest? I like to reach the point where the Enclave show up, and then they set up patrols across the wasteland. Adds even more gun fights on top of the random encounters (triggered in specific spots sometimes) and raiders, beasts, etc. Its very rare in this game that you can walk far without running into something. And travel by foot a bit more, it adds to the game experience. You'll encounter more things.