I cannot begin to stress enough the importance of being punctual for an interview! It is absolutely critical that you show your potential employer that you are reliable, responsible, and flat out want the job. Nothing leaves a more sour taste in an employer's mouth than having to wait to interview a possible candidate for a position. There are no excuses. If you are unsure about the location of the establishment, drive the route the day before. If there is a possibility of traffic being an issue, schedule that into your departure time.
Wedding Crashers Rule #76: No excuses, play like a champion
Stack the odds in your favor. Don't be late.