Adding a second string of x-values?

I have a series of charts that I’m working on that display the maximum authorized speed (Y-axis) on a rail line over a numerical distance (X-axis). What I’d like to do is add text for stations or other points of interests along the line corresponding to their distance, but I can’t seem to figure out how to do so.

Can you share an example of what you’ve tried so far to help us help you?