Guard/Guide Rail – Friend or Foe?
Guardrails, technically called guide rails in Ontario, are so common along our roadsides that most motorists do not even notice them. While they are generally effective at protecting motorists from serious roadside hazards, such as bridge piers, steep slopes, or bodies of water, injuries can result from collisions with guide rails. Ontario crash statistics reveal that 37% of crashes associated with guide rail collisions result in property damage, 32% in slight injuries, and 25% in moderate injuries 1. Severe injuries occur in 3% and fatalities in 2% of guide rail associated crashes.
Design, construction, repair and maintenance flaws can have a significant effect on guide rail performance; but even proper care cannot guarantee that guide rail crashes will not result in injuries. It is important to evaluate both the guide rail system and the crash event itself, because even if flaws exist, they do not always affect the outcome of a specific crash.
Figure 1: The pole may be too close to the guide rail and the guide rail end.
Sometimes crash conditions differ substantially from design criteria. Guide rails are crash-tested by vehicles selected to represent the vast majority of passenger vehicles (e.g., vehicle weight, size, type) under reasonably severe crash conditions (e.g., speed and angle of impact). The maximum collision energy for guide rail testing is represented by a 2000 kg vehicle striking the guide rail at 100km/h at an angle of 25 degrees. When actual crash conditions exceed this energy or the vehicle characteristics are substantially different from those used in the crash test, the guide rail may not work as designed. Some severe crash outcomes may be attributed to a mismatch between tested condition and actual field installation.
Figure 2: A potential spearing hazard has been created at an improper termination in a construction zone.
Some of the common guide rail flaws include:
- Too low/high to engage the vehicle, which results in over/under-ride or vehicle tripping.
- Too close to the shielded object, which may allow contact with hazard despite the guide rail.
- Improper anchor at one, or both sides of the shielded object, causing collapse.
- Missing, deteriorated or improper components (such as bolts, posts and cracks).
- Improper termination, causing spearing (penetration of guide rail into vehicle) or launching/tripping of the vehicle.
- Too short, so an errant vehicle cannot stop safely behind it.
- Placed behind a curb, so that a vehicle is launched before reaching the guide rail.
- A combination of different types and rigidity of guide rails, causing vehicles to spin-out.
- When the guide rail itself is a greater hazard than the object being shielded.
When a guide rail is struck during a crash, an expert can evaluate whether its design or installation is flawed and whether this flaw likely contributed to the severity of the collision. Since guiderails are typically repaired quickly, it is important to document guide rail damage immediately after a collision.
1 Ontario Motor Vehicle Accident Database – combined 1st, 2nd and 3rd Events (2005-2009).