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Ideally, at the moment of impact, a vehicle should have all wheels on the ground and the suspension system in a neutral state. Thus, terrain conditions between the traveled way and the barrier are very important. For example, curbs should be avoided and should be no higher than 4 in (100 mm) if used. In […]

Factors to consider in specifying the exact layout of a barrier at a given location include lateral offset from the edge of the traveled way, terrain effects, flare rate, and length of need. (See also Art. 6.10.) 6.7.1 Lateral Offset Roadside barriers should generally be placed as far from the traveled way as condi­tions permit, […]

In most cases, the selection of a roadside barrier should be made on the basis of the system that will provide the required degree of shielding at the lowest cost. The lowest cost should be based on a life-cycle cost analysis, considering initial and maintenance costs None 10 in x 12 in x 7 in […]

The concrete safety shape system (Fig. 6.21), which has a sloping front face, is similar to the concrete median barrier (Art. 6.9.1) but usually has a vertical back face. The reduced cross-section of the roadside barrier version makes it more vulnerable to over­turning, thus requiring more reinforcing steel and/or a more elaborate footing design. The […]

The box-beam (weak-post) system (Fig. 6.16) achieves its resistance through the com­bined flexural and tensile resistance of the box beam. Posts near the impact point are designed to break or tear away and distribute the impact force to adjacent posts. This system meets TL-3. The system is sensitive to mounting height and irregularities in terrain. […]

TABLE 6.2 Classification of Roadside Barriers and Approved Test Levels Barrier system Test level Flexible systems Three-strand cable (weak-post) TL-3 W-beam (weak-post) TL-2 Modified W-beam (weak-post) TL-3 Ironwood aesthetic barrier TL-3 Semirigid systems Box-beam (weak-post) TL-3 Blocked-out W-beam (strong-post) Steel or wood post with wood TL-3 or plastic block Steel post with steel block TL-2 […]

Depending on their deflection characteristics upon impact, roadside barriers can be classified as flexible, semirigid, or rigid. Table 6.2 lists the most widely used barriers in each classification. Details of most of these operational barriers are presented along with other available information in Figs. 6.13 through 6.22. The dynamic deflection listed is that observed during […]

Roadside obstacles include nontraversable terrain and fixed objects, either constructed (such as culvert headwalls or structural supports) or natural (such as trees). Such obstacles account for over 30 percent of highway fatalities. The need for a barrier depends on both the nature of the obstacle and the probability that it will be hit. Table 6.1 […]

As indicated in Fig. 6.12, the main factors considered in determining the need for barriers are the embankment height and the side slope. These criteria are based on studies of the severity of encroachments on embankments as compared with impacts with roadside barriers. The figure does not include the probability of an encroachment or relative […]

Longitudinal roadside barriers are used to shield motorists from natural or human — made obstacles located along either side of the traveled way, and sometimes to protect pedestrians and bicyclists. Median barriers and barrier end treatments are discussed separately in Arts. 6.9 and 6.12. Barriers must contain and redirect vehicles. Because of the complicated dynamic […]