An intermediate size pipe culvert is defined as a single round pipe with more than 36-in diameter or multiple round pipes each with more than 30-in diameter but having maximum diameter of 60-in in and a total opening (i.e., distance) of 20-ft or less between extreme inside faces as measured along the highway centerline. For arch pipes, use span dimension instead of diameter.

Intermediate size single box culverts are defined as those having only one barrel with maximum height of 60-in. Cross-sectional area of the single box or individual pipe normally should not exceed 25-ft

2

.

The openings of intermediate size single barrel box and pipe culverts are too large to be safely traversed by a vehicle. Recommended safety treatment options should be considered in the following order:

Sloped end treatments with safety pipe runners are preferred from a safety standpoint and are generally cost effective for both new and existing intermediate size culverts, regardless of end location with respect to clear zone criteria. These end treatments should be sloped at a rate of 1V:4H or flatter within the clear zone, 1V:3H outside the clear zone, and should match the side slope rate thereby providing a flush, traversable safety treatment.

Length of new culverts should be governed by the locations of the side slope plane/culvert intercepts rather than by clear zone. Terrain near the culvert end should be smoothly shaped and traversable, and headwalls should not be used.

For existing intermediate size single barrel box and pipe culverts, no treatment is necessary for culvert end offsets beyond the clear zone and below the traffic volume threshold as shown in . Where an improved design is warranted using , the removal of headwalls and installation of sloped ends with safety pipe runners is the preferred safety treatment.

In certain situations, treatment with safety pipe runners may be impractical (e.g., culvert skew exceeds 15 degrees or severe debris problems). For these conditions, locating intermediate size culvert ends to meet desirable clear zone values (see ) is preferred over shielding with barrier. Designs having flared wing walls with safety pipe runners oriented parallel to the stream flow and spaced at 30-in maximum center to center thereby can minimize debris problems. The orientation of pipe runners must also consider the direction of mainlane traffic and be selected properly for cross drainage or parallel drainage.