I could never let my 10 month old female run around outside either. My male I could (though I dont, I take them out on leashes) because he is afraid of strangers and doesnt like the road.. Aerowyn .. however.. likes people very much, expecially children. There is a man who drives a motercyle down the street and if I'm in the front yard with her she will look up and trot after him until her leash gets to the end of it. O_O I know its hard sometimes to keep cats inside (We have a porch with a door so its a bit easier for us) you probably will just have to watch your door better. My cats try to sneak outside the main door somtimes but we can catch them 80 percent of the time. Also maybe you should think about investing in leashes and harnesses? pet stores should sell cat harnesses and leashes ( I reccommend retractable) and sometimes you can find cheap leashes at discount stores ( we have a liquidators down the road and I bought two, 25 foot leashes for three dolllars each (compared to like 13 each at kmart or petco/petsmart) Cat harnesses are usually pretty cheap also, the one i bought for my girl kitten cost only four dollars, though I had to buy a small dog harness for Elliot because he is a big cat( it cost me like 7 or 11 dollars. i dont remember O_O I think 11 though). They might not like the harneses and leashes at first, but if you put the harnesses on them inside the house for a while, and try to get them used to a leash, you could at least take them outside for a while and let them walk around ( mine are a bit better than most because they would stay in the back yard even w/o leashes, and they usually just lay around in the back yard) O_O Hope that helps a bit! I know some people cant stand to let their cats be inside only cats so a leash and harness, besdies an escape proof area, are your best bets.
Heck if its just that ONE cat then it should be alot easier than training all three of them. Hm... have you ever tried tying cans to the back of your car, and having him in a carrier or something, anpull up into the driveway? or drive by on the street? (might want to do this sometime when it wont bother anyone, lol) :P your cat might get so freaked by the noise it wont go on the street anymore