Why Is Offset Block Used In Highway Guardrail Systems

highway guardrail offset block featured image

The highway guardrail plays an important role in terms of protecting motorist’s safety and reducing casualty or damages caused by vehicle accidents.

The highway guardrail nowadays is consisting of w beam or thrie beam plate, guardrail post, and offset block.

The definition

The offset block is made of profile steel material. It is normally hot dipping galvanized with electrostatic spray coating to have longer durability. The Chinese standard defines the size of the offset block is 196 x 178 x 200 x 4 mm. The cross-section is a hexagon shape. The design provides a flexible distortion spacing when being hit.

However, the offset block is not the only choice for doing its job. According to the anti-collision level of the road guardrail, there is also the offset bracket. Although the offset block has a better performance on the offset bracket, the cost can be 3-4 times higher.

Therefore, in the real world, the offset block is always seen in the highway where the 4mm thick guardrail and post with a diameter of 140mm is used. The offset bracket, on the contrary, is used in a normal road or suburban road where the guardrail thickness is 3mm.

offset bracket installation
offset bracket
hexagon shape offset block
highway guardrail offset block
round shape offset block
round type offset block

The function

The guardrail plate and the post are connected by an offset block, which is also called block out. The offset block acts as a force bearing and energy-absorbing part.

When the vehicle is colliding with the guardrail plate, the impact energy will be transferred to the offset block, causing its deformation. The deformation adsorbs parts of the force and the energy to protect the driver and passengers from careening off the main road and striking objects out of the guardrail by deflecting the vehicle back in the right direction.

Besides, the offset block is rigidly connected to the guardrail plate and the post, it can spread the impacting force to more areas all across the guardrail track. So the offset block is also and reinforcement to the highway guardrail.

the function of offset block
offset block before and after being crashed
the deformed offset block
the deformed offset block

The advantages of using offset block

  1. The hollow design offset block sits between the guardrail and the post. The hollow space keeps the guardrail from touching directly with the post. When an errant vehicle strikes onto the guardrail, this space gives time for a possibility of deflection.
  2. The offset block can absorb the impacting energy by a distortion. It helps to reduce the severeness of damage from the accident.
  3. For the road with curb, the offset block narrows the distance between the curb and the guardrail, reducing the possible damage caused by the jumping vehicle.
  4. The existence of the offset block makes the highway guardrail even stronger because it helps to transfer the striking force to the whole guardrail structure evenly.
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