Hi Smock
I'm not sure if you wanted an expert or current student to respond. But I feel your pain so I just wanted to chime in. I actually interviewed on this past Tuesday for Sloan, so I can definitely relate to the nerves and stress of it all.
I'm sorry you had bad luck with the traffic and all! I'm sure it has definitely happened before. At this point, spilt milk right? Maybe you could have brought up the huge accident as small talk, but then again maybe the interviewer didn't notice? My interview started about 5 minutes behind schedule.
It's great that they complemented you and were positive during the interview. For me, I walked out feeling confident about the majority of my answers. And felt great that I had finished my last interview and I had done all that I could do to give myself good chances at a couple schools. I'm trying not to stress about it (as much as possible). Of course, the more I think about it I wish I could've pointed out xyz and emphasized abc. But in the end, it is what it is. I hope I communicated with Sloan my passion for their program and the excitement I have to contribute.
Good luck to us both. Hope your stress has already subsided, if not hope I was able to help..