Yes. All airlines overbook, just as hotels, rental car companies and many other travel vendors do. If they didn't, they would not be able to survive. They would wind up with far too many empty seats. In deciding how much to overbook, they rely on their past experience to be able to predict approximately how many people will cancel or simply not show up for a particular flight.
However, you needn't worry. Airlines must ask for volunteers to take later flights before involuntarily bumping anyone. Airlines typically offer a free ticket or $$ to volunteers and rarely have trouble getting enough volunteers to take a fight to their destinations a few hours later than planned.
Just be sure you get assigned seats when you make your reservations and plan get to the airport early enough so that you can comfortably get through that unexpected traffic jam, get through the longer than anticipated check-in line and get through that longer than normal security line in time to board timely.