Chapter 4 - Elements of Design

4.3. Vertical Alignments

4.3.3. Minimum Vertical Grades

Minimum vertical grades are typically used to facilitate roadway drainage. This is especially true of curbed roadway sections where drainage or gutter spread is a consideration.

Uncurbed Pavements

For projects involving uncurbed pavements, longitudinal grades may be flat (0%) in areas where appropriate cross slopes are provided. In areas of superelevation transitions and/or flat cross slopes on those projects, minimum vertical grades should be consistent with those listed in Table 4.6.  Minimum Vertical Grades for Roadways where Drainage Spread is a Consideration. However, there are situations with uncurbed pavements where it is prudent that consideration be given to maintaining minimum vertical grades - similar to those for curbed roadway sections. These situations include:

• a new location rural section

• roadways with high truck percentages that experience appreciable pavement rutting

• current rural roadways in urban, suburban or developing areas that have a realistic chance of being converted to a curb and gutter sometime in the foreseeable future

• areas containing superelevation transitions and/or flat cross slope areas
• interstate or other high speed facilities

Table 4.6. Minimum Vertical Grades for Roadways  where Drainage Spread is a Consideration
Type of Facility	Minimum Grade (%)
	Desirable	Minimum
Industrial Roadways with Curb and Gutter Local Urban Streets with Curb and Gutter Urban Collectors with Curb and Gutter Urban Arterials with Curb and Gutter Urban Freeways or Limited Access Facilities	0.30 0.30 0.50 0.50 0.50	0.20 0.20 0.30 0.30 0.30

Curbed Pavements

For curbed pavements, minimum longitudinal grades are controlled by the values in Table 4.6. This includes roadways with concrete median barriers or side barriers, V-gutter and those roadways adjacent to walls. These values will generally ensure that roadway “spread” is not excessive and can be contained within acceptable ranges by a minimum (reasonable) number of roadway drainage catch basins. The minimum values in Table 4.6 should be used only under extreme conditions.