All motorists are familiar with the guardrails that line our nation's streets and highways. We're all familiar with their purpose – to prevent vehicles from straying off the road into dangerous areas such as bodies of water or forests. What most people aren't aware of is that guardrails have gone through many different designs over the past 50 years.
Guardrails initially all had blunt ends, which was fine for a vehicle that came into contact with the middle of the guardrail. However, they posed a serious risk to a vehicle that impacted the guardrail from the upstream end. Acting similar to a spear, the blunted end of the guardrail would pierce the grill, wheel well or side door of the vehicle and lodge its way into the passenger compartment, causing severe injury or death to any passenger in its path.
Eventually, guardrails were switched to a twist turn-down design in which the end of the guardrail was twisted 90 degrees and anchored into the ground. This solved the problem of vehicles impacting the blunt end of the guardrail, but this particular design also served as a ramp, causing vehicles to rollover.
Today, the most commonly used design is the W-Beam guardrail with large flat surfaces on the end to absorb the impact of any vehicle that comes in contact with it. The first energy-absorbing end terminal to be placed at the end of guardrails was the ET-2000, though several other designs have been used as well.
A recent study by the University of Alabama at Birmingham (UAB) School of Engineering analyzed data from eight years of crashes that resulted in fatalities or serious injuries in Missouri and Ohio. The study was designed to compare the relative safety of the ET-2000 design and three other designs:
- Flared Energy Absorbing Terminal (FLEAT)
- Slotted Rail Terminal (SRT)
- The ET-Plus
While the study concluded that the sample size was not significant enough to glean meaningful conclusions from comparing the FLEAT and SRT designs to the ET-2000, it was able to compare the ET-Plus to its predecessor, the ET-2000. Interestingly, the study found that the newer design – the ET-Plus – was 36% more likely to cause severe injury and 186% more likely to cause a fatality.
The researchers cautioned that more studies would need to be done and that the results of this study should not be considered conclusive, but the study serves as an important step towards evaluating and understanding the relative safety of the different designs.