I think a colon would be the most apt punctuation here.
The tracks are now unruly and wild, the people tied to them: killed in crosswalks
But to be honest I was fine with no punctuation. The bit that most bothers me is the choice of preposition. You don't go in a crosswalk. You go on it. Or maybe you're at the crosswalk when you're killed. But certainly not in.
Grammar has so many "technically correct" yet odd sentence structures.
The sentence definitely has a weird flow and could absolutely contain reader assistance via punctuation.
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 don't think that word is required. If anything, I think
sometimes you come and pull the lever
sounds more natural, if you have to add a word. They're speaking more colloquially, rather than formally, but I don't think the original is grammatically incorrect.
Seriously though, as much as I hate that we've abandoned so many railroads in this country, even the urban ones should at least be turned into walking/biking trails once they stop being used. It's ridiculous to drive past overgrown train tracks and think, "I wouldn't even need a car if those things were in use, but as it is right now it isn't even safe to use them as a footpath."
A former switchyard in the town where I grew up got turned into a beautiful park and there are trails going through town where the railroad tracks went. Obviously a trolley or some other sort of passenger rail would be better, but at least make that otherwise useless land some sort of public good.