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25 CHAPTER 3 SUMMARY OF STATE SURVEYS ON CURBS AND CURBBARRIER COMBINATIONS INTRODUCTION Sloped curbs are designed to be low with flat sloping faces so that vehicles can cross them readily. AASHTO Type B, C, The objective of this research project was to develop design D, E, F, and G curbs, shown in Figure 18, are all typical guidelines for using curbs and curbbarrier combinations on sloped curbs. Types B, C, and D are considered to be mount- roadways with operating speeds greater than 60 km/h. Seven able under emergencies. The vertical portion on the lower tasks were identified to accomplish this objective. The second face of Types C, D, and F is constructed as an allowance for of these tasks was to conduct a survey of transportation agen- future resurfacing. All the sloped curbs shown in Figure 18 cies to determine current practice, guidelines, and standards can be used as shoulder curbs to control drainage, improve pertaining to the use of curb and curbbarrier combinations delineation, and reduce erosion. on higher-speed roadways. The survey was also intended to The survey respondents indicated the type or types of identify problems experienced by transportation agencies curbs they used for facilities with a design speed of 65 km/h and solutions developed to counter those problems. or greater: AASHTO Type A vertical curb or Type B, C, D, The research team composed a three-page survey (pro- E, F, or G sloped curbs. A summary of the results is presented vided in Appendix A) and distributed it to all 50 states. The in Table 5. survey included 12 questions covering the types of curbs Five states indicated that they used Type A vertical curb used, the guidelines for using them, the typical functional pur- although two of those states indicated that it was not used poses of curbs, alternatives to using curbs, safety problems for speeds much greater than 65 km/h. Three other states encountered, using curbs in combination with barriers, curb employed a curb similar to Type A with a few minor modifi- research, and voids for establishing guidelines. Twenty-seven cations in the dimensions. Thirteen states employed a Type B states completed and returned the survey. Their responses are sloped or similar curb. Type B was used by more of the organized by topic. In lieu of the state's name, when refer- responding states than any of the other curbs. Type C and ence is made to individual states, a numeric identifier is used. Type D had a similar response, with seven states using each or a comparable version with slightly modified dimensions. Types E and G also had a similar response. Type F had the TYPES OF CURBS USED BY THE STATES lowest response rate: only one state used a sloped curb that was similar to Type F. Additionally, seven states identified According to AASHTO, curbs are used extensively on all curbs used in their jurisdictions that could not be categorized types of urban highways but should be used cautiously on with the AASHTO curbs. Seven distinct curbs were identi- rural highways. There are two general classifications of curbs: fied, shown in Figure 19. vertical curbs and sloped curbs. Some raised aspect or verti- Most of the states had guidelines or policies in place for cal element is required to be considered a curb. Vertical curbs when vertical or sloped curbs should be used. Only six states are relatively high and steep-faced. They used to be called indicated that they did not have policies, two of which indi- barrier curbs, but this terminology is no longer used because cated that they followed AASHTO guidelines. these curbs are not redirective devices or traffic barriers. Eight states indicated that they limit the use of curb by AASHTO Type A curb, shown in Figure 17, is a vertical curb facility type. State 8 did not use curbs on roadways with that ranges in height from 150 to 225 mm. It is designed to design speeds greater than 70 km/h with the exception of inhibit or discourage vehicles from leaving the roadway. asphalt concrete dikes. State 13 also restricted their use to Vertical curbs should not be used on freeways and are con- roadways with design speeds less than 70 km/h, but noted that sidered undesirable on high-speed arterials. AASHTO rec- exceptions exist, particularly in urban areas. State 25 limited ommends that vertical curbs not be used where design speeds their use to facilities with design speeds under 80 km/h. State exceed 65 km/h, except in predominantly urban or rapidly 3 limited their use to nonaccess-controlled highways. State developing urban areas in the intermediate speed range. 7 and State 10 limited their use to urban streets. State 18 only