Going for an interview is like going for a first date. You want to look and behave your best at your first date/interview, to grab your potential date/employer's attention. Like in a date so in an interview, you get only one chance to create an impeccable first impression, to prove why you are the perfect match for the job.
Emergencies happen. Sure. You can't control the accidents on I-5 freeway, or the bus drivers showing up late. But you can definitely be prepared. Commute to the site of your interview before the day of your interview. See how long it takes to get there. On the day of your interview, give yourself enough time to be there early, even IF unexpected circumstances arise. With all that said, if you are still running late, CALL the interviewer! It's common courtesy. And there is almost a zero-percent chance of getting called back if you are late AND don't call to let them know.