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28 depressed freeway sections. State 4 used portable New Jer- sey shape concrete barrier along the edge of highways for drainage channelization. State 12 used pavement striping or flexible tubes in lieu of curbs for channelization. State 16 used open ditches for drainage but noted that it is not appro- priate at most locations where curbs are specified. State 19 used drainage ditches or swales in place of curbs for drainage Figure 20. Schematic drawing used in the State Survey to and berm guards or other safety barriers to protect vehicles identify curb and barrier placement along roadways. from steep slopes. State 9 used concrete traffic separators in the median. State 25 used a unique curb and gutter adjacent to the travel lane on facilities of greater than 80 km/h. State 24 used a traversable curb that is more like a gutter or berm rail. The authors assume they are referring to a form of non- than a curb. The curb has no reveal and is 100 mm high and yielding, metal beam guardrail (i.e., not cable). The type of 305 mm wide with a 1:3 slope across the top. The curbs used curb used differed greatly. Regarding offset distances, four by States 25 and 24 are included in Figure 19 as A5 and A6, states recommended the curb be placed offset from the bar- respectively. rier, though at distances that varied greatly; one state placed the curb under the barrier; and most states placed the curb face flush with the barrier face. The responses are summa- PREVIOUS CURB SAFETY PROBLEMS IDENTIFIED BY THE SURVEY rized in Table 6. The states were also asked if they had experienced any Only five states indicated that they had experienced safety problems with curbbarrier combinations on higher- safety problems when using curbs alone on higher-speed speed roads. Three states had experienced safety problems. roadways. However, two states indicated that they did not State 6 had experienced vaulting with the 150-mm curb that use vertical curbs on facilities with posted speeds in excess was resolved by only using sloped curbs on higher-speed of 70 km/h and one state indicated it only had ten miles of facilities. State 19 had also experienced vehicles vaulting. curbed high-speed highway in its system. Of the five states The respondent did not elaborate on how this problem was that experienced safety problems, only four states provided solved but did state that even with the curb face flush to the further information. State 25 had experienced cross-median barrier, vehicle wheels can get caught between the curb and fatalities with curbs along higher-speed roadways; median the guardrail. State 27 had experienced W-beam rail failure guardrail was installed to resolve this. State 9 indicated at the splice and switched to ten-gauge rail on all Interstates that it had had problems with vertical curb installed on a and ramps for roadside applications. 90 km/h urban Interstate in the 1960s and was replacing the vertical curb with sloped curb or concrete barrier. State 19 had experienced problems with vaulting and rollover of PREVIOUS CURB-RELATED RESEARCH vehicles in the tests performed for the Midwest State's CONDUCTED BY THE STATES Regional Pooled Research Program. State 27 also experi- enced problems with vaulting. This state reported that curbs Survey respondents were asked if their states had con- are not typically used alone, but rather in combination with ducted any research related to curbs or curbbarrier combi- a guardrail and for protection from runoff or erosion of a nations. Seven states indicated that they had conducted or steep slope. were currently participating in research on curbs or curb barrier combinations. Three states had participated in the Pooled Fund Study by the Midwest Roadside Safety Facil- CURBBARRIER COMBINATIONS ity entitled "Guardrail and Guardrail Terminals Installed over Curbs." One state had conducted crash tests of 100-mm The states were also asked about curb and barriers used in and 150-mm curb beneath guardrail and determined that the combination. The survey included the illustration in Figure 20. 100-mm-high curb met the criteria of NCHRP Report 350, The survey respondents provided the type of curb used, the Recommended Procedures for the Safety Performance Eval- type of barrier used, the offset distance from the edge of the uation of Highway Features. The 150-mm-high curb did not travel lane to the face of the guardrail or barrier (distance A meet the criteria. in the illustration), and the offset from the face of the curb to the face of the guardrail or barrier (distance B in the illustra- tion). Many states indicated that they tried not to use the two VOIDS FOR ESTABLISHING GUIDELINES in combination. Three states said they did not use them in combination on higher-speed roads. Seven states responded The states were asked to identify the most critical void for that guardrail was used but did not specify the type of guard- establishing guidelines for using curbs and curbbarrier com-