these are really a lot harder to do than i thought when I started on mine. Part of the problem is that they tend to be foreground items and very visible!
I finally went the simple route and trimmmed a piece of sandpaper (same as I use for asphalt roads) and after gluing it to some styrene to bulk it up a bit, just glued it in place. Done!
If you are lucky enough (or plan better than me...) and have straight track at your crossings, you can use pre-scored Evergreen styrene sheet that has the score lines in it to match scale wood planking. Some brown paint like Jeff has done here and you're done.
A modern precast concrete and rubber crossing is going to take some work....anyone game?