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.
To everyone who can’t figure out the missing word, it’s “the people once tied to them ‘WERE’ killed in crosswalks…”
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
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.