This was my fifth Indy and we had no problems with traffic, pretty much like every other year. Got off at Crawfordsville Rd, park at any one of the dozens of places blocked off, or in someones front yard near the track (for a price, of course) and walk the 1/2 mile or so to the gate thats between turn 4 and the pits. Left Cincinnati about 8:30 and by 11:00 we were already in our seats, and we were going at a very leisurely pace at that.
Certainly a huge volume of people, but everyone was remarkably well behaved, crowds moved fairly orderly, and the police had the roads set up and directed traffic in a way worked very well. We left about 10 minutes after the race ended, it was about a 15 minute walk to the car, and within 10 minutes after that we were on the interstate and never hit a big backup anywhere. Not even really any slow traffic, just a short backup on Crawfordsville trying to get to I-465. By 6:30 pm I was already back in Cincinnati, checked in at a downtown hotel, cleaning up to meet the wife and friends at the Taste of Cincinnati.
I've spent much, much more time trying to get out of parking lots and hitting backups on the highway after a Reds or Bengals game, or after a concert, much worse than anything I've seen trying to get out of Indy after the race.
I've only been to five 500's but this year was by far the hottest. I mean seriously, obnoxiously, horrendously, relentlessly hot. Very little breeze where we were in the stands, the sun was fierce, and even with copious amounts of sunscreen, I got a lot of sun on my arms, legs, and neck. I saw some seriously sunburned people walking out after the race. A few times clouds covered the sun and there was a collective cheering in the crowd the times that happened, it was the only relief you had.
Castroneves smacked the wall right in front of us, you dont have a good idea amazingly how loud that is until it happens right in front of you.
If this is on your bucket list of things to do, I definitely recommend it. My only complaint (other than the heat this year) is you are really packed in up in the stands. You have about a foot and half space to park your rear end and most people have coolers, which will go between your feet, so if crowds and tight spaces arent your thing, watching from up in the stands wont be too enjoyable. The cars are also pretty loud, so consider bringing earplugs, lots of people were using them.