Performance of Longitudinal Barriers on Curved, Superelevated Roadway Sections (2019) / Chapter Skim
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From page 18... ...
18 Literature Review and State DOT Survey 2.1 Introduction A detailed literature review was conducted to gather infor mation and synthesize relevant past efforts. The focus was on studies related to the design, performance evaluation, mainte nance, and application details of longitudinal barrier systems when placed on CSRS with emphasis on crash testing and computer simulations.
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19 • For installations on side slopes, the performance of barriers placed behind the hinge point was significantly worse than when placed before the hinge point. This was the case even though all barriers were installed in relatively gentle slopes (shallower than 4H:1V)
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20 impact conditions consistent with updated crashworthi ness criteria. 2.3 Terrain Effect Studies A more recent study, not directly related but relevant to the topic of this research, was conducted at the Texas Transportation Institute (TTI)
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21 Case 1 Barrier at 13.25 ft Case 2 Barrier at 23.5 ft 34.00 32.00 30.00 28.00 26.00 24.00 0.00 5.00 10.00 15.00 20.00 25.00 N o m in al b u m p er h ei g h t (i n ) Lateral position of the bumper (ft)
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22 showed that the barrier met all NCHRP Report 350 criteria in both cases. It is noted from these simulations that the 813mm (320in.)
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23 2.4 General Curve Safety Guidance Another reference related to the topic of this research is NCHRP Report 500: Guidance for Implementation of the AASHTO Strategic Highway Safety Plan, Volume 7: A Guide for Reducing Collisions on Horizontal Curves (Torbic et al.
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24 2.5 Road Design Guidelines A few guidelines were obtained from respondents of the state DOT survey. An initial review showed that these guide lines are similar to the Green Book recommendations sum marized in the following subsection.
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25 2.5.1.2 Maximum Superelevation Rate Vehicles traveling on curved roads are subjected to a lat eral force known as centrifugal force. This lateral force, which pushes the vehicle outward from the curved road center point, increases as the vehicle speed increases or the radius of the curve decreases.
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26 2.5.1.4 Minimum Curvature Radius The minimum curvature radius defines the sharpest curva ture for a given design speed, maximum superelevation, and maximum side friction factor. It can be expressed as follows: 15 0.01 max max min 2 R V e f D ( )
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27 • Only flexible and semirigid barriers should be installed on slopes steeper than 10H:1V. • A barrier should be placed as far as possible from the trav eled way as practical without hindering its proper operation and performance.
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28 focused on Wbeam, Thriebeam, and concrete barriers of various heights. The information received was grouped and ranked as shown in Table 2.5.
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29 shown in Table 2.6. Concrete barriers were listed most often (by 25 of the 33 states)
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30 barrier in the median of a CSRS because of repetitive hits on the guardrail. One state had a segment of roadway that was the subject of an improvement project to permit the guard rail removal because motorists rebounded from the guardrail into the traveled way of an opposing lane, or else impacted the guardrail on the opposite shoulder.
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