Traffic jam at midnight

At about 11:45 last night, I was woken by the sound of loud honking from multiple cars. — definitely not a random car alarm. After about 10 minutes of this, I went to the window and this is what I saw. Mine is a tiny street leading to nowhere in particular, with a major avenue going the same direction only two blocks away, so we generally have very light traffic, especially late at night. I have no idea what caused this bizarre exception.