Highway Guardrail

Highway Guardrail: What is it’s Purpose?

Did you ever give though to what that Highway Guardrail is actually doing?

The main purpose of a highway guardrail along the highway is to form a safety barrier to help protect a motorist who has drifted off the road.

If a car is running off the road for one reason or another, the best thing that can happen is for that car to come to rest unimpeded.

Sometimes, however, that is not possible and that is where guardrails come in.

In certain places on any given stretch of road, the roadway might have steep embankments or side-slopes next to it, or even be lined with trees.

highway guardrail - Highway Guardrail: What is it's Purpose?
Highway Guardrail Purposes

Utility poles, bridge piers and retaining walls are other obstacles. In these cases, striking a guardrail would be greatly preferable to striking the obstacles, so guardrails are usually installed.

They lessen the severity of a potential crash and make the roads safer.

The guardrail can act in a myriad of ways from deflecting a vehicle back onto the road, slowing it down or stopping it, or in some cases just slowing it down enough and allowing it to proceed past the guardrail.

Guardrails are not a 100% failsafe, but they do help.

Obviously the size of the vehicle and the speed with which it hits the highway guardrail plays a part in how effective the guardrail is in slowing a vehicle.

Before guardrails are installed, engineers weigh all the potential factors to make sure that the placement works as well as possible in all conditions.

The guardrail itself functions as an entire system rather than just stand-alone pieces. Each piece serves a different purpose as part of the whole. Everything from the posts that are driven into the ground to the way the guardrail connects to the post is important and plays a part.

The end terminal and the anchoring system at the end terminal is just as important. But overall, the highway guardrail basically consists of two key parts; the guardrail face and the end terminal.

  1. The guardrail face is exactly what it sounds like; the part that extends from the terminal along the road. Its function is simple and always the same: to redirect a vehicle that runs into it back onto the roadway.
  2. The end terminal is the starting and ending point of the guardrail and is also referred to as the end treatment. The end needs to be treated with some kind of energy absorbing treatment because the impact from a vehicle is absorbed and then slides down the rail. The end terminal functions in two 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 in this instance the guardrail is pushed through, much like the action of a gate opening.
highway guardrail - Highway Guardrail: What is it's Purpose?
Highway Guardrail

A guardrail system is always put through performance tests before it is actually installed along a roadway. The performance of the system is assessed through crash tests that are done in a controlled environment. You can click here to see more about Highway Guardrail Performance direct from the Federal Highway Administration

Safety professionals use certain criteria to determine if the system meets standards.

The guardrail face test is used to determine if a car is directed back onto a roadway when it meets the rail.

The end treatment tests are then conducted by having a vehicle strike the rail dead-on and also at an angle. This will determine if the system is properly absorbing energy from a vehicle.

For head-on impacts, the end treatment should absorb most of the energy so that the guardrail can gate or extrude, and the vehicle can pass through.

This will slow the vehicle down as it passes behind the guardrail, allowing it to come to rest with minimal damage.

The tests used to test a guardrail system are usually conducted at about 60 MPH, so it is important to understand that if a vehicle hits the guardrail at higher speeds, the system may not operate properly.

highway guardrail - Highway Guardrail: What is it's Purpose?
Purpose of a Highway Guardrail

Very high speeds are especially troubling because guardrail systems are simply not meant to accommodate vehicles traveling far above posted speed limits.

The faster the vehicle is going when it strikes the guardrail, the more damage might occur because the energy demonstrated is so much more.

Even a guardrail system that is working at peak performance can only absorb so much energy.

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