3km would be the maximum range you'd expect to acheive. It is when you pretty much have no obstacles between you and the other unit. If you are in a built up area the CB will still work but the range will reduce.
EG: Me and my bro got about 3/4 of a km out of our little toy walkie talkies when I was out in the boat and he was on land. Those things wouldn't work 200m in the suburbs.