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curbs. States were asked to separately rank the functional
purposes of vertical and sloped curbs used in their state. Most
states identified drainage control as a primary or secondary
purpose for vertical curb. Walkway support and pavement
delineation were also highly rated as typical functional pur-
poses of vertical curb. Only one state said the primary use
of vertical curb was to protect vehicles from steep slopes.
Respondents also identified other functional purposes of ver-
tical curb not listed on the survey, including minimizing
Figure 17. AASHTO vertical curb Type A (1 = 25.4 mm). right-of-way impacts, access control, accommodating pedes-
trians, aesthetics, erosion control, delineating edge parking,
and traffic channelization.
The primary functional purpose of sloped curb was most
used 76-mm asphalt or 100-mm lip curbs for design speeds often listed as drainage. Twenty-four states listed it as the pri-
greater than or equal to 80 km/h. State 19 responded that it mary or secondary purpose. Pavement delineation was listed
did not restrict their use, but noted that the policy was that by 14 states as a primary or secondary functional purpose.
curbs are undesirable for use on roadways with design speeds One state listed walkway support as a primary functional
greater than 80 km/h. State 24 also responded that it did not purpose, and several others listed it as a secondary purpose.
restrict their use, but its roadside design guide prohibits the Protecting vehicles from slopes was listed as a secondary pur-
use of nonsloped curb on new construction projects on high- pose by three states. Respondents also wrote in other func-
ways with operating speeds greater than or equal to 80 km/h tional purposes of sloped curb including erosion control,
and along the mainline of Interstates, freeways, or high-speed minimizing right-of-way impacts, access control, pedestrian
parkways. needs, channelization, and delineation.
TYPICAL FUNCTION OF CURBS ALTERNATIVES TO USING CURBS
AASHTO lists drainage control, pavement edge delin- Eight survey respondents had found an alternative to using
eation, right-of-way reduction, aesthetics, delineation of pedes- curbs for one or more of the functional purposes mentioned in
trian walkways, reduction of maintenance operations and the previous section. State 5 used sloping freeway curbs with
assistance in orderly roadside development as purposes of catch basins to prevent embankment erosion in the gutter on
Figure 18. AASHTO sloped curbs (1 = 25.4 mm).
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TABLE 5 Vertical and sloped curb use among the states surveyed
Number of states
Number of states
AASHTO curb using a curb similar Total
using this curb
to this curb
Type A Vertical 5 3 8
Type B Sloped 6 7 13
Type C Sloped 5 2 7
Type D Sloped 6 1 7
Type E Sloped 3 1 4
Type F Sloped 0 1 1
Type G Sloped 2 3 5
A1 A2
A3 A4
A5
A6
A7
Figure 19. Curbs used by various states that could not be classified as
AASHTO curbs.
