BARRIER AND TREATMENTS

Early traffic barrier designs often paid little attention to the ends of the barriers, so they either ended abruptly in blunt ends, or sometimes featured some flaring of the edges away from the side of the barrier facing traffic. Vehicles that struck blunt ends at the wrong angle could stop too suddenly or have steel rail sections penetrate into the passenger compartment, resulting in severe injuries or fatalities. As a result, a new style of barrier terminals were developed in the 1960s in which the installers were directed to twist the guardrail 90 degrees and bring its end down so that it would lie flat at ground level (so-called "turned-down" terminals). While this innovation prevented the rail from penetrating the vehicle, it could also vault a vehicle into the air or cause it to roll over, since the rising and twisting guardrail formed a ramp. These crashes often led to vehicles flying at high speed into the very objects which guardrails or barriers were supposed to protect them from in the first place.

To address the vaulting and rollover crashes, energy-absorbing terminals were developed. The first generation of these terminals in the 1970s were breakaway cable terminals, in which the rail curves back on itself and is connected to a cable that runs between the first and second posts (which are often breakaway posts). The second generation, in the 1990s and 2000s, feature a large steel impact head that engages the frame or bumper of the vehicle. The impact head is driven back along the guide rail, dissipating the vehicle's kinetic energy by bending or tearing the steel in the guide rail sections. A guide rail may also be terminated by curving it back to the point that the terminal is unlikely to be hit end-on, or, if possible, by embedding the end in a hillside or cut slope.

All barrier must be made with so carefull..

An alternative to energy absorbing barrier terminals are impact attenuators. These are used for wider hazards that can't be effectively protected with a one-sided traffic barrier.