I wasn't going to post this, but then I realized that I might be able to save others from having a similar experience to me. I've been using the Waze navigation app for almost a year now and generally love it. It still has the occassional hiccup, like the time it decided to get me across DC diagonally by going left-right-left-right-left-right across all the blocks, but there have also been times it's been a real boon. Driving through New Jersey, there's been more than one occassion where it's had us get off the turnpike and route around a traffic jam.
Much of the power comes from crowd sourcing. The servers are tracking the users and can see where they are being slowed down. Unfortunately, I found a failure case a couple weeks ago.
I was on my way through Pennsylvania via I81. Apparently, there was a BAD accident that closed the highway for something like 50 miles. Where I would normally get on, they had blocked off the entrance, and such was the case a long way. Everyone who had been on had been shunted off, and no one was getting on. I think this totally foobared the Waze system. With no one on the road, no one could report a problem or demonstrate it by be stopped. Waze had no data indicating that there was even a slow down. Worse, because people had been shunted off onto surface road, Waze tried to be helpful by shunting me around the resulting congestion which actually took me 20 miles in the wrong direction, where it then told me to get on the clearly closed highway.
Not being familiar with the area, I spent over an hour trying to find ways to convince Waze that the road was closed. You can report road closures, in theory. But you're actually limited to declaring intersections within about of half mile of you as closed. This meant that I could declare the on ramp closed, but then I was just rerouted to the next closed on ramp. I guess I could have done this for mile after mile, but that would have involved driving right through the center of Harrisburg in the least efficient way possible.
In the end, I had to dead reckon my way up the side of the river until Waze finally found another bridge to get me across, and then took me through 50 miles of wilderness area. By this time it was getting dark and I was down to 1/8th of a tank of fuel. The first gas station I passed was closed.
Panic time. "I'm out in the land where gas stations actually close. I'm screwed." Actually, then I hit a town with an open station/convenience store. After I got my blood sugar up, I wasn't ready to reroute to Waze headquarters via the nearest novelty jumbo croquet mallet store. We just have to accept that in a algorithmic world, edge cases can really ruin your day.