So far, the "Passing Index" (I was going to call it something along the lines of "excitement rating", but I was correctly admonished by commenter "Jason" that passing does not necessarily equal excitement) has simply looked at the amount of position changes per race. But some races are longer than others, which likely leads to more passing. And, sometimes passing happens near the front of the pack which is probably more exciting/interesting than passing at the back of the pack.
Short Track: Update On Passing Index
So, we'll first add a measurement to evaluate the passes per minute. Also the rank for the race is now shown to the right of the score. (Same limitations apply as in the original description for these, linked above, such as the shortcuts I'm taking to get to the "position changes".)
Provides a bit of context, for instance Atlanta was 5th in Position Changes, but moves up to #3 in the per-minute index since it was such a short track (median lap time 48 seconds) with a decent number of position changes. And Anaheim 1 drops down two spots because even though it had a fairly large number of position changes, it was a moderately long track (median lap time 64 seconds).
On top of that, we'll introduce an "excitement" measure after all, but describe it as Passing "Excitement" index since it only reflects passing, not how close the race was, or if there were crashes, or comebacks, or whatever--things that may affect how exciting the race was. All the measurement does is weight passes into position 1 the highest, into position 2 the next highest, all the way down the line. It also provides a bump if there was a pass into podium position in the last three laps.
Please take the "excitement" rating for passing with a grain of salt. But, I still think it's moderately interesting, and we see that San Diego 1 is the top race for passing in all three measures. In "excitement", Anaheim 1 jumps back up, largely because there was Jason Anderson coming up from very far behind all the way to #1, and Ryan Dungey made a Lap 20 pass into 2nd place. Anaheim 2 makes it into the top 3 for "excitement" as it had Eli Tomac and Ken Roczen coming from the back of the pack into the top four, plus Roczen passed Tomac for 3rd at the end of Lap 20. Arlington falls a bit because of its 130 position changes, only 10% occurred in the top 6 spots (compared to 20% at San Diego 1 or even 17% last week at Toronto).
Take the Passing Index for what you will. This chart probably doesn't change your life, but it gives some insight into the courses, I think. There are factors it can't capture, of course, like what effect Justing Bogle's first-lap crash had to the position changes at Toronto. But the thing I like best is how clearly it shows that San Diego 2 was a bad track for passing, which was a universal complaint from riders and fans after the race.