and are anchored to small bases by bolts that will shear and separate the pole from the base when struck by a vehicle (see Figure 14-2). Similar break-away technology also has been applied to highway signs (see Figure 14-3).
Guardrails have become a common design feature for major highways, replacing
wooden poles with steel wire rope strung between them. Initially, guardrails had an end
at the same height as the rest of the guardrail. When a vehicle struck the end of the guardrail
just right, the guardrail entered the windshield and pierced through the passenger com-
partment. Today, the ends of some guardrails extend below ground level. In some loca-
tions where the end cannot be buried, a telescoping, energy-absorbing segment is used to
terminate the guardrail. Figure 14-4 illustrates some guardrail features.
Early interstate highway designs had a variety of protective barriers for bridges and
other locations. Subsequent experience and research led to better barrier designs that
prevent vehicles of various sizes from overriding them. Today, there is a standard barrier
with a unique cross-sectional shape (see Figure 14-5). These barriers are used in perma-
and are anchored to small bases by bolts that will shear and separate the pole from the base when struck by a vehicle (see Figure 14-2). Similar break-away technology also has been applied to highway signs (see Figure 14-3).
Guardrails have become a common design feature for major highways, replacing
wooden poles with steel wire rope strung between them. Initially, guardrails had an end
at the same height as the rest of the guardrail. When a vehicle struck the end of the guardrail
just right, the guardrail entered the windshield and pierced through the passenger com-
partment. Today, the ends of some guardrails extend below ground level. In some loca-
tions where the end cannot be buried, a telescoping, energy-absorbing segment is used to
terminate the guardrail. Figure 14-4 illustrates some guardrail features.
Early interstate highway designs had a variety of protective barriers for bridges and
other locations. Subsequent experience and research led to better barrier designs that
prevent vehicles of various sizes from overriding them. Today, there is a standard barrier
with a unique cross-sectional shape (see Figure 14-5). These barriers are used in perma-
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