Why do you think that traditional martial arts don't work in actual combat?
Experience and history.
Seriously, every traditional martial artist I've seen has had their ass handed to them in a real fight. I've done some of the handing myself.
It might have to do with the overemplasis on forms that most traditional arts have. Forms are great, don't get me wrong, they force the body to develop muscle memory and force the student to develop visualisation and concentration skills. Unfortunately most guys miss the whole point of forms and blaze through them, not even knowing what the hell the motions they are doing represent. Thus in a real fight, they often perform worse than people with no experience whatsoever.
It also might have to do with the sheer lack of strategy in traditional arts. Each art has their own strength, unfortunately most of the time it doesn't teach you how to keep a fight in a phase that benefits you. Case in point, Wing Chun is a friggin awesome art at close range. You can trap your strikes so effectively...except for one problem...how do you get into that range? Same thing with Karate/TKD. They advocate a one strike philosophy...but how do you set that strike up? All one has to do in a fight is to go outside an art's comfort range and that practitioner is majorly screwed.
Which goes to the ultimate point: most traditional arts suck at grappling. And most fights end up in that phase. Even the traditional grappling arts are all but useless if you are up against someone without a gi on. Sorry if it sounds like I am preaching, but I have seen way too many people who have a black belt in TKD or Karate or some sort of Kung Fu get wasted in street fights.
But ultimately it is your decision, and starting off with the intro classes sounds like a good idea.
Good luck with your training, and I hope that you never have to experience a real fight. Lord knows that I wish I did not have to.