Comment by decimalenough

That's not how it works. Maps will see that the average speed of cars around Chinatown has slowed to a crawl, and it will route drivers elsewhere. They also get lists of planned closures from local traffic agencies, and you'll see these clearly displayed in black and red with little stop signs. (The quality of this data obviously varies wildly though.)

Accidents on highways are a different story because there are rarely any alternatives, or if there are, they're so much slower that it still makes sense to suffer through the 30 min jam.