The reason our government has highway guardrails across this country along federal, state and local highways, is to form a safety barrier to help protect motorists who have drifted off the road. If a car is running off the road for one reason or another, the best outcome that can happen is the car comes to a rest unimpeded. However, sometimes that is not possible and that is where guardrails come in.
On any given stretch of a road, in certain areas, the roadway may have steep embankments or side-slopes next to it, or even be lined with trees. Utility poles, bridge piers and retaining walls are other obstacles where guardrails are installed. They help lessen the severity of a potential crash and make the roads safer.
The guardrail acts in many different ways from deflecting a vehicle back onto the road, to slowing it down, to stopping the vehicle, or in some cases just slowing it down enough and allowing the vehicle to progress past the guardrail.
Guardrails are not a 100% failsafe, but they do help. The size of a vehicle and the speed in which it hits the highway guardrail plays an important part in how effective the guardrail is in slowing a vehicle down.
Even before you see a guardrail on the road, highway engineers weigh all the potential factors to make sure the placement and type of guardrail used is effective as possible in all kinds of weather and road conditions.
The setting up of a guardrail itself has the guardrail functioning as an entire system rather than just stand-alone pieces. Each piece serves a different purpose as part of the whole system. Everything from the equipment and machinery it takes to drive a post into the ground to the way the guardrail connects to the post is significant and plays an intricate part in the success of the guardrail system. The end terminal of the guardrail and the anchoring system at the end terminal play just as an important part. Overall, the highway guardrail basically consists of two key parts- the guardrail face and the end terminal:
- The guardrail face is the part that extends from the end terminal all along the road. It has the basic function of redirecting a vehicle that runs into the guardrail face back onto the road.
- The end terminal is the starting and ending point of the guardrail and is also known as the end treatment. The end terminal needs to be treated with some kind of energy absorbing treatment because the impact from a vehicle is absorbed and then slides down the guardrail. The end terminal functions in two different ways:
- If a vehicle hits head-on, the impact head slides down the guardrail redirecting it away from the vehicle until the energy from the impact has dissipated and the vehicle has come to a stop.
- When a car hits at an angle, the impact head may extrude the guardrail or gate out, allowing the vehicle to pass behind the guardrail. So when a car hits at an angle, the guardrail is pushed through, just like the action of a gate opening.
The tests by the Federal Highway Administration to determine the safety of a guardrail and the end terminals are conducted at around 60 MPH. Vehicles traveling at very high speeds are especially troublesome because guardrail systems are not meant to accommodate vehicles traveling in far access over the posted speed limit. The faster a vehicle is going when it strikes the guardrail, the more damage will occur because the energy of the impact is so much greater. Even a guardrail system working at peak performance can only absorb so much energy.
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