They are saying you can't simply drive past the 365 cars. You need to observe those 365 cars for the entirety of your commute. Otherwise comparing 365 drive by comparisons to your 365 commutes isn't exactly the same.
So, it’s more like you observe somewhere in the range of 5-10 cars for the duration of the commute depending on how densely you’re surrounded on average? That’s really interesting, and if you see 1 mistake per commute, then the average driver is actually quite a bit worse than the gp assumed!
The unit I'd use is car-minutes. In a 30-minute commute you might observe 200 car-minutes (this is a total shot in the dark to be clear) closely enough to notice a mistake if it happened. So if you notice 1 mistake per commute on average, and you yourself make a mistake every 200 minutes of driving, you could estimate that you're an average driver.
