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26 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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27 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.