In 1846 train tracks were laid down into 10th, 11th and 12th avenues and used to transport cargo easier into the industrial areas of New York City.
Thus, there were so many pedestrian accidents that something had to be done at street level to help curb deaths and accidents by wandering New Yorkers who happened to be not paying attention as they walked.
So, the Hudson River Railroad, who operated the trains, brought in the Cowboys!! The West Side Cowboys, that is.
These cowboys were shipped in from the west and their main job description was to mount their horses and ride in front of the trains while waving a red flag to warn pedestrians of an oncoming train. Although this helped a little, there were still hundreds of adults and children who were killed and injured from these trains; thus, giving the name Death Avenue to 10th Avenue in particular.
To prevent more deaths, an elevated railway called the High Line was built in 1933. The first train ran on the High Line—which was then called the “West Side Elevated Line.” The line was fully operational by 1934, transporting millions of tons of meat, dairy, and produce. At some points, the lines cut directly through some buildings, creating easy access for factories
In 1941, 90 years after the cowboys were started, the West Side Cowboys trail rides came to an end as trains stopped running at street level. Train use dwindled in the 60's thru the 80's due to the rise in trucking. The southernmost section of the High Line, from Spring to Bank streets, was demolished in the 60s. The decline continued through the 70s, with all traffic stopped by the 80s. Calls for total demolition of the structure soon followed.
And that is how the remaining sections became the park that is now The High Line.