A small culvert is defined as a single round pipe with 36-in or less diameter, a single box culvert with span of 36-in or less, or multiple round pipes each with 30-in or less diameter, each oriented normal to the roadway. (Note: For arch pipes, use span dimension instead of diameter.)

When skews are involved, the definition of a small pipe culvert is modified as shown in .

Small pipe culverts with sloping, open ends have been crash tested and proven to be safely traversable by vehicles for a range of speeds. Small culvert ends should be sloped at a rate of 1V:4H or flatter within the clear zone, 1V:3H or flatter outside the clear zone, and should match the side slope rate, thereby providing a flush, traversable safety treatment. Single box culverts normal to the roadway with spans of 36-in or less may be effectively safety treated just as small pipes.

When vulnerable to run-off-the-road vehicles (i.e., unshielded by barrier), sloped ends should be provided on small culverts regardless of culvert end location with respect to the clear zone dimensions. For existing culverts, this often entails removing existing headwalls and may include removing the barrier treatment if it is no longer needed to protect an obstacle other than a culvert end.

For new culverts or existing culverts that may need adjusting, culvert pipe length should be controlled by the intercept of the small pipe and the side slope planes. Side slopes should not be warped or flattened near culvert locations. Also, terrain near the culvert ends should be smooth and free of fixed objects, and headwalls should not be used.