The original overpass uses way too much filament. I cut out some large chunks of the models for a quicker print. I've split the main part into two pieces with pins that connect for easy glueing.
Note that you may need to print at 105% scale - I found the overpass slightly too narrow.
Print the sides with the ramp part up in the air (as pictured). No supports should be needed. Print the two body parts with the flat side down. Glue together with a few drops of super glue.