Does Anybody Know What Caused the Back-Up on NYS Thruway on 8/21?

My niece and her daughter were up visiting her parents in Albany and my Mom wanted to see her Great Grandchild --so I agreed to drive her up there. It takes about 2 1/2 to 3 hours each way depending on whether we stop at one of the rest stops on the way-which we did going up. I wasn't sure if we were even going to go yesterday because my Mom kept seeing that it was supposed to rain. But at 7:30 I was woken up by the telephone--"can you get here by 8:30"--I made it! Half asleep but I made it!! Clear sailing all the way--no problems. We had a wonderful time then left around 3:30 because I have to be home before dark. I am almost totally night blind now from the condition that affects my eyes. Again--clear weather-clear sailing--BUT--we kept seeing signs that stated that all lanes were closed after exit 15. Now we could have gotten off and taken a lesser known bridge then the Tappan Zee but there was really no traffic-so I kept driving. No rest stops on the way home-I just wanted to get there! THEN----just after Exit 15--barricades--we were forced off onto another road that took us into New Jersey--I could not get to the place I should have been so I ended up on Route 17. There was traffic but nothing like on the other side of the road!! Meanwhile my Mom found a map-------she hates not knowing where she is or where she is headed. I was finally able to spot a gas station and the guy told her to keep going in the direction we were going then get on 4 East-it would take us to the George Washington Bridge. Remember we are now also in the middle of people driving home from work. Once we hit the bridge and managed to get over it I knew exactly how to get her home from there!! She finally recognized where she was and put away that map!! I dropped her off and got home at 8:00 PM -I just made it before it got dark - to a very angry and upset Cat!! Meanwhile I had to at least attempt to do some of the Facebook threads that I had joined in on before I realized we were actually going--I still have to finish up the comment groups. I may put this in a couple of them tomorrow although I am letting it post today.

Meanwhile I searched the internet and can not find out what caused that calamity. Does anybody know anything about it? Please tell me in the comments!!