BUilding a new road, culvert suggestions?

[rScotty]

Most effective trash racks will be smooth pipe or tubing 4 to 6 inches apart with the lower ends on or in the dirt in the bottom of the ditch with the upper end higher then the culvert it is protecting, this is laid at a low angle to allow the trash to push up and over or off the rack.

Right on. The low angle is the key. You want the water to be able to push trash up the rack so the water flows under.
rScotty