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From page 150... ... 150 SELECTION GUIDELINES The following section presents the recommended selection guidelines and the process for the application of the guidelines for the selection of MASH TL2 though TL5 bridge railings. A risk approach applicable to new construction, rehabilitation and retrofitting is recommended. Read the entire page →
From page 151... ... 151 2. Encroachments – Estimate the total number of encroachments (NENCR) Read the entire page →
From page 152... ... 152 local transportation routes, however, detours would be possible and reasonable. Penetrating the railing has the possibility of causing at least one non-motor vehicle injury or fatality. Read the entire page →
From page 153... ... 153 f. Regional concerns about snow removal, hydrological impact of flood waters flowing over the bridge, and maintaining scenic views may also play a role in the selection of bridge railings beyond these selection guidelines. Read the entire page →
From page 154... ... 154 Table 67. Encroachment Adjustments. Read the entire page →
From page 155... ... 155 Table 68. AADT – Lifetime Encroachments per 1,000-ft of Bridge Railing. Read the entire page →
From page 156... ... 156 Figure 30. AADT – Lifetime Encroachments/1,000-ft of Bridge Railing Nomograph. Read the entire page →
From page 157... ... 157 Figure 31. Minimum Horizontal Curve Radius Based on Barrier Obstruction to the Stopping Sight Distance Compared to AASHTO Exhibit 3-14. Read the entire page →
From page 158... ... 158 LOW MEDIUM HIGH Figure 32. Test Level Selection Nomograph (Risk<0.01 in 30 years for 1000 ft of bridge railing) Read the entire page →
From page 159... ... 159 Discussion Implementation The LRFD Bridge Design Specifications address the issue of the selection of the appropriate test level for bridge railings in Chapter 13 Section 13.7.2 and the Roadside Design Guide addresses the same issue in Chapter 7 Sections 7.3 and 7.5.[AASHTO11, AASHTO12] Section 13.7.2 of the AASHTO LRFD Bridge Design Specification provides general principles for selecting the appropriate test level for bridge railings. Read the entire page →
From page 160... ... 160 Critical Values for Design The recommended guidelines use a risk-based method where the risk of observing a severe or fatal crash (i.e., A+K) during the design life of the bridge railing was less than 0.01 per 1000-ft of bridge railing. Read the entire page →
From page 161... ... 161 The cost-benefit rehabilitation selection figures assume that a Report 350 TL3 or TL4 bridge railing is already in place and must be demolished and replaced by either a MASH TL4 or TL5 bridge railing. Test Levels Considerations Currently, FHWA requires that roadside hardware developed and tested after January 1, 2011 be evaluated according to the AASHTO MASH but still allows the use of hardware designed, tested and accepted under Report 350. Read the entire page →
From page 162... ... 162 wood railing that were designed for Report 350 TL2.[TF1313] The construction costs of these new TL2 railings are not well documented since there have only been a handful of installations constructed. Read the entire page →
From page 163... ... 163 type ends at the AADT corresponding to the transition from level of service C to D for 40 PT. The engineer is also told explicitly in Step 2b not to extrapolate to the right of the highway type lines because doing so will violate the basic assumptions used to develop the tables. Read the entire page →
From page 164... ... 164 While a MASH TL6 bridge railing might be appropriate for some conditions above the dotted risk line, there is at present only one crash tested TL6 bridge railing, the 90-inch tall TX T80TT bridge railing. Read the entire page →
From page 165... ... 165 was expanded to add the first line to represent the approximately equivalencies for MASH test levels. Table 70. Read the entire page →
From page 166... ... 166 1989 GSBR and 22-08 Findings Risk≤0.01 overlaid on 89GSBR Risk≤.03 overlaid on 89GSBR Figure 33. Comparison of 89GSBR, NCHRP22-08 with Risk values. Read the entire page →
From page 167... ... 167 1989 GSBR and 22-08 Findings BCR=2 overlaid on 89GSBR BCR=5 overlaid on 89GSBR Figure 34. 89GSBR, NCHRP22-08 with BCR values. Read the entire page →
From page 168... ... 168 A MASH TL2 satisfies risk and costbenefit criteria. Read the entire page →
From page 169... ... 169 Table 71. Selected Examples of Existing Bridge Railings Compared to the Recommended Selection Guidelines. Read the entire page →
From page 170... ... 170 Table 71. Selected Examples of Existing Bridge Railings Compared to the Recommended Selection Guidelines. Read the entire page →
From page 171... ... 171 Table 71. Selected Examples of Existing Bridge Railings Compared to the Recommended Selection Guidelines. Read the entire page →
From page 172... ... 172 Table 71. Selected Examples of Existing Bridge Railings Compared to the Recommended Selection Guidelines. Read the entire page →

From page 150...

... 150 SELECTION GUIDELINES The following section presents the recommended selection guidelines and the process for the application of the guidelines for the selection of MASH TL2 though TL5 bridge railings. A risk approach applicable to new construction, rehabilitation and retrofitting is recommended.