I think it’s correct as-is. Inserting a “were” would make that clause read as independent. With how the sentence is currently structured, that doesn’t work.
That’s not to say you couldn’t have
The tracks are now unruley [sic] and wild—the people once tied to them were killed in crosswalks by giant trucks
if you want, but the comma needs to change to something like a dash or a semicolon. With a comma (i.e., as a subordinate clause), “were” doesn’t make sense.
I am pretty sure Ubuntu is still far and away the most popular desktop distro. For servers I would have guessed it was something like RedHat/CentOS or possibly Debian.