Abstract. We will study some strange traffic rules for cars driving through an interchange: When they enter via an underpass, they just go through. But when they enter via an overpass, they fall down to the underpass with some small probability $p$, and then keep going unharmed, down under.

We will learn that to analyze this traffic game we need matrices and that to play it better we need probabilities that are not numbers between 0 and 1. We will also learn how this game can be used to define some knot invariants (a notion we will explain) which may be the best we presently have.

URL. https://drorbn.net/cumc26.

Handout. Traffic.pdf, Traffic.html, (source files: pensieve).

Talk Video@YouTube.

Talk Video (mp4).