Interesting, thanks for compiling. But I think there are some inconsistent data that really affects the numbers. For example, the Atlanta streetcar is listed at 2.7 miles long. That's the total length of all of the track, which operates one-way on paired streets (like parts of Portland's system). But then the DC streetcar is listed at 1.9 miles, while on wiki it's listed as both 2.2 and 2.4 miles, but really the total track length is double that number. Same story for systems like SLC's S line. It's listed as 2 miles, but that's really 4 miles of track.
If something operates more as a loop the total track length is counted, but if something is two-way on a linear path only half the actual track length counts. This makes ridership appear to be 50% of what it actually is on one-way paired systems.
My point is, if this is intended to be a useful comparison across systems, the denominator has to be the same. What does "per mile" mean? Is it per track mile, or per route mile?
Also a quick correction on the ridership for the Atlanta streetcar, since it's not from the wiki source. It's from
here. He says "about 1000 per day," which is true, but the exact number is 1105 per day (100,608 passengers in the first 91 days of 2016). Also of note is this is daily ridership, not weekday ridership, but as far as I know the actual daily counts have never been released. One final note is that 2015 ridership was much higher, when the system was free.
Just to show how big of a difference all of these assumptions and data choices make:
-Using the data in your spreadsheet now, the Atlanta streetcar is listed at 370 daily riders per mile.
-Using a route length of 1.35 miles and
ridership numbers from 2015, it would be 1641 daily riders per mile.