Roadway design breaks down into four basic categories; Restricted or triangular gutter flow, sheet flow, retrofit or repair work, or curb return applications. Triangular gutter flow applications are typically seen next to a barrier wall or in the gutter of a curbed section of roadway This design method is also used where a trench drain is placed in a valley. Sheet flow applications are often seen at driveway entrances, across streets without a crown, or access ramps on and off of limited access roadways. Retrofit or repair work is typically seen where an inlet did not get placed in the low point making a sloped trench drain system an easy fix. Curb return systems are placed in the radius of an intersection to keep wheelchair ramps dry and eliminate problems with complex grades associated with placing an inlet structure close to the radius of an intersection.
Roadway systems should meet all AASHTO H-20 load ratings and all AASHTO M309 ratings. There should be no flow restrictions inside the trench cross section to catch debris. Grates should be ductile iron. UV light and thermal degredation eliminate the use of any plastic components.