Recommended Guidelines for the Selection of Test Levels 2 Through 5 Bridge Railings (2021) / Chapter Skim
Currently Skimming:
Pages 82-149
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 82... ...
82 DEVELOPMENT OF BRIDGE RAIL SELECTION GUIDELINES The available analysis methods and software products presented in the literature review assess the probability of a roadside feature being struck, the severity of the crash if it has occurred and the resulting crash costs through conditional probabilities then perform a benefit-cost analysis of roadside design alternatives to determine the most costeffective design. RSAPv3 has the added capability of tabulating crash costs such that the lifetime risk of a specified crash severity can be calculated independent of the direct costs (i.e., construction, maintenance and repair costs)
|
From page 83... ...
83 coding problems. In any case, a great deal has changed in the types of bridge railings that are available today in comparison with the early 1990s as reflected in the NCHRP 22-08 report.[Mak94]
|
From page 84... ...
84 Table 23. New Jersey Turnpike Crash Severity Distribution.
|
From page 85... ...
85 determined and the results and distributions are shown in Table 25. The percentages of penetrations and rollovers were determined and confirmed using available narratives of the police reports.
|
From page 86... ...
86 Table 26. Massachusetts After Barrier Contact Behavior.
|
From page 87... ...
87 these crashes; including one that resulted in a fatality. Six of the remaining 13 crashes resulted in non-incapacitating injuries (level B)
|
From page 88... ...
88 The vehicle landed in an unused area under the bridge; a fortunate occurrence as this bridge spans South Fork Tenmile Creek (Route 188) , a 5,000 vehicle per day state route, and a set of railroad tracks.
|
From page 89... ...
89 The 42" F-shape bridge rail had no PRV failures for both the 55 mi/hr and 65 mi/hr speed zones. The number of incidents for each bridge rail and speed zone where a vehicle rolled over after being redirected by the bridge rail are tabulated in Table 30.
|
From page 90... ...
90 Figure 19. Ohio Standard Drawing BR-1 [OH11a]
|
From page 91... ...
91 Table 31. Ohio Crash Severity Distribution.
|
From page 92... ...
92 Table 32. Ohio Bridge Rail After Barrier Contact Behavior.
|
From page 93... ...
93 Table 33. Nebraska Crash Severity Distribution.
|
From page 94... ...
94 Table 33. Nebraska Crash Severity Distribution.
|
From page 95... ...
95 Table 35. Severity Distributions for After Penetration Hazards Hazard K A B C PDO/UNK Total Embankment in 55 mi/hr Speed Zones No.
|
From page 96... ...
96 Table 36. Total Encroachment Frequency by AADT and Highway Type.
|
From page 97... ...
97 mid-life number of encroachments and then uses that value in calculating the expected crash costs. If the mid-life ADT turns out to be on the top of the "hump" the encroachments would be overestimated for the entire life and if the mid-life ADT occurs at the bottom of the "trough" the encroachments would be underestimated.
|
From page 98... ...
98 c.g. location)
|
From page 99... ...
99 Figure 20. Mean Axle Load by Vehicle Classification.
|
From page 100... ...
100 used was 75 percent passenger cars and 25 percent pickup trucks. This strategy results in the traffic mix for each percentage of trucks shown in Table 38.
|
From page 101... ...
101 Table 39. Vehicle Properties Used in RSAPv3.
|
From page 102... ...
102 Using passenger vehicle trajectories would include some trajectories that are clearly difficult to attain for heavy vehicles. Passenger vehicles are smaller, have better braking and acceleration characteristics as well as different inertial properties.
|
From page 103... ...
103 model the vehicle encroachment frequency. The vehicle type is unknown in this dataset since the data was based on tire marks, however, data collectors were instructed to focus on passenger vehicles.
|
From page 104... ...
104 REGIONAL DATA The New Jersey Turnpike has a continuous TL5 concrete median barrier from milepost 1.2 to 104.7. Since the median barrier is continuous and relatively close to the left shoulder it is similar to a direct measure of primary and opposing left encroachments.
|
From page 105... ...
105 Table 40. National Traffic Volumes, Crashes, and Crash Rates by Year.
|
From page 106... ...
106 πΆπ
πΆπ
= ππΆπ
π where: CRT = Crash Rate of Trucks and Buses (crashes / 100 MVMT) , CRA = Crash Rate of All Vehicles (crashes / 100 MVMT)
|
From page 107... ...
107 Table 43. NJ Turnpike Ran Off Road Left Crash Rates, 2005.
|
From page 108... ...
108 Table 44. NJ Turnpike Ran Off Road Left Crash Rates, 2006.
|
From page 109... ...
109 Table 45. NJ Turnpike Ran Off Road Left Crash Rates, 2007.
|
From page 110... ...
110 Table 46. NJ Turnpike Ran Off Road Left Crash Rates, 2008.
|
From page 111... ...
111 Table 47. Truck/Bus Crash Rate Multipliers, by Year and Link.
|
From page 112... ...
112 Encroachment Adjustments for Site-Specific Characteristics The 1989 AASHTO GSBR includes three adjustment factors; a horizontal curvature adjustment factor, a grade adjustment factor and an adjustment factor for deck height and under-structure conditions. The adjustments for the grade and horizontal curvature from the 1989 AASHTO GSBR are shown in Table 48 and Table 49.
|
From page 113... ...
113 bridge railing. The area under the bridge is accounted for in the selection tables and described in full in a later section.
|
From page 114... ...
114 selection. Doing so is conservative for narrower shoulders.
|
From page 115... ...
115 Figure 21. RSAPv3 Crash Prediction Module Flow Chart.
|
From page 116... ...
116 Table 50. Bridge Railing Load Capacities.
|
From page 117... ...
117 conform to the 1989 GSBR PL1 but there was probably still relatively little inventory of PL2 or PL3. It is assumed in Table 51, therefore, that the crash data is mainly representative of PL1 railings.
|
From page 118... ...
118 Table 51. RSAPv3 Predictions of Penetration and Rollovers compared to NCHRP 22-08 TXDOT Crash Data.
|
From page 119... ...
119 Table 52. Comparison to Crash Data of RSAPv3 predictions of Penetrating, Rolling over or Vaulting the Bridge Railing for all Vehicle Classes.
|
From page 120... ...
120 potential for another harmful event if the vehicle is redirected (e.g., rolling over in the roadway or striking another barrier) or leaving the bridge structure and falling to the area below the bridge.
|
From page 121... ...
121 EFCCR65 appropriate for use when the vehicle penetrates, rolls over or vaults over the barrier is discussed in the next section. Bridge Railing Penetration Severity For purposes of estimating crash severity, the 1989 GSBR and NCHRP 22-08 assumed that penetrating the bridge railing resulted in a 35 ft drop.
|
From page 122... ...
122 for the shipment of goods or transportation of people, and/or damage to an urban area which is not densely populated (i.e., single family homes, single office buildings, etc.)
|
From page 123... ...
123 Costs When conducting an RSAPv3 analysis, the crash costs of each feasible alternative are determined. A benefit-cost ratio (B/C)
|
From page 124... ...
124 beneficial at lower traffic volumes. Conversely, a shorter service life amortizes the construction cost over a smaller period so higher performance railings would be costbeneficial at higher traffic volumes.
|
From page 125... ...
125 vocational rehabilitation. This list of cost components is essentially the same as that used by Miller in his 1988 study of nationwide crash costs.
|
From page 126... ...
126 Figure 22. Lane-Mile Cost Comparison by State.
|
From page 127... ...
127 Table 56. Crash Cost Adjustments by State to the National Average.
|
From page 128... ...
128 Figure 23. Regional Crash Cost and Construction Cost Adjustment Factors Relative to a Base of One.
|
From page 129... ...
129 Temporal Cost Variations Further compounding the regional variations in costs are the variations of costs in time due to general economic variations. For example, the U.S.
|
From page 130... ...
130 fatal injury and O for a property damage only crash) and results in a different comprehensive cost.
|
From page 131... ...
131 . Figure 25.
|
From page 132... ...
132 discussed later, but first the costs and adjustments used in the development of the benefit-cost tables are presented. Bridge Railing Agency Costs Construction Costs Construction bid prices for various test level bridge railings from a variety of states were reviewed, adjusted and averaged using the NCHHI index and WSDOT study discussed above to determine the 2012 national average construction prices shown in Table 58.
|
From page 133... ...
133 foot. After applying the state and annual factors then averaging the values, a resulting 2012 value of $23 per linear foot was obtained as the national average cost per linear foot for the removal and disposal of bridge rail.
|
From page 134... ...
134 Table 59. Annual Number and 2005 Cost of Truck Crash by Injury Severity and Truck Type.
|
From page 135... ...
135 The FMCSA updated these costs to reflect the FHWA 2008 updated VSL. These updated 2008 costs are shown in Table 60.
|
From page 136... ...
136 Table 61. NSC Economic Impact Crash Costs.[NSC11]
|
From page 137... ...
137 Table 63. Summary of the Cost of Bridge Rail Crashes Investigated by NTSB.
|
From page 138... ...
138 distance on highways or streets that have two or more traffic lanes in each direction of travel." [AASHTO01] When "horizontal sight distance on the inside of a curve is limited by obstructions" measurements are taken at an average of the stopping sight distance and passing sight distance height (i.e., 2.75 ft)
|
From page 139... ...
139 be used as minimum radii. The Green Book recommendation for the HSD object height is 33 inches.
|
From page 140... ...
140 Table 64. Minimum Radius and Maximum Degree of Curve Based on the HSD Obstruction from a TL4 or TL5 Bridge Railing.
|
From page 141... ...
141 β’ Encroachment characteristics over the project life at low traffic volumes (i.e., averaging out the Cooper data "humps") , β’ Vehicle mix characteristics, β’ Penetration, rollover, and vault potential for each test level of bridge railing, β’ The severity of a bridge rail penetration if it does occur, and β’ An improved understanding of how temporal and regional variations in crash costs and construction costs impact the development of national guidance development.
|
From page 142... ...
142 Benefit-cost analysis has been a valuable tool in roadside safety for nearly 35 years and has been used to both prioritize specific projects as well as develop state and national guidelines for barrier selection and placement. One the one hand, benefit-cost analyses helps transportation agencies make the most effective use of their limited roadside safety funding.
|
From page 143... ...
143 where, P(k) = Probability or risk of observing k failures (i.e., severe or fatal crashes)
|
From page 144... ...
144 RSAPv3 uses the so-called Cooper data to estimate the number of encroachments as a function of highway type and AADT. The Cooper data, which was collected over a wide area in Canada in the 1970's, along with the statistical methods used to develop the relationships pictured in Figure 27 are discussed in much more detail in the RSAPv3 Engineer's Manual.[Ray12]
|
From page 145... ...
145 Figure 27. Cooper Encroachment Frequency Data [after Ray12]
|
From page 146... ...
146 Estimate the Probability of a Severe or Fatal Crash in Any Encroachment The probability of a severe or fatal crash occurring in each particular collision is the next parameter that needs to be calculated for applying the binomial distribution. RSAPv3 uses the conventional police-reported crash severity (i.e., the KABCO scale)
|
From page 147... ...
147 level bridge railing given that a crash occurs so they are only dependent on the vehicle mix (i.e., percent of trucks) and the hazard environment.
|
From page 148... ...
148 characteristics influence the number of encroachments to be expected but not the severity of any particular crash. The severity is influenced by the area under the bridge (i.e., High, Medium, Low)
|
From page 149... ...
149 Table 66. Probability a Collision Will Result in a Severe or Fatal Injury by Hazard Environment and MASH Test Level.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.