By Roger Bligh, Contributing Author
When a vehicle leaves its intended course of travel and collides with an object, another vehicle or overturns, that is called a roadway departure crash. These types of crashes represent roughly 50% of roadway fatalities in the United States.
Roadside safety hardware refers to a family of devices designed to reduce the severity of roadside crashes. These devices include guardrails, median barriers, bridge rails, crash cushions, end treatments and breakaway support structures.
The Texas A&M Transportation Institute (TTI)—where I manage the Institute’s Roadside Safety Program—has designed, tested and evaluated such safety devices for most of its 75-year history.
I’ve worked at the TTI for nearly 40 years. As electric vehicles (EVs) become more prevalent on North American roadways, recent crash tests reveal that existing roadside safety barriers may not adequately protect EV occupants.
Tests conducted by TTI and the University of Nebraska–Lincoln’s Midwest Roadside Safety Facility (MwRSF) show that guardrail systems, compliant with safety standards for internal combustion engine (ICE) vehicles, fail under EV impact conditions due to factors such as increased weight, lower center of gravity and unique vehicle design characteristics.
With EV adoption projected to rise, researchers stress the need for updated roadside safety standards to prevent fatalities and ensure crash barriers accommodate evolving vehicle designs.
Making Safety the Standard
The current testing standard for these devices is the American Association of State Highway and Transportation Officials’ Manual for Assessing Safety Hardware (MASH). Today’s 276-page document began in 1962 as a single page—yes, one page—of recommendations titled Highway Research Circular 482.
A barrier system that meets MASH standards is expected to contain and redirect a vehicle impacting within design parameters to keep the vehicle from going through, over or under the barrier to prevent a motorist suffering a fatal or serious injury during a crash.
When vehicle specifications change, the MASH standards for testing roadside devices used to contain those vehicles must sometimes change too. Recent testing of EVs using MASH criteria established for ICE vehicles shows that some existing roadside barriers are inadequate when EVs impact them.
Looks Can Be Deceiving
While EVs might resemble their ICE counterparts, the physics that define how each type of vehicle interacts with roadside barrier systems can be different.
In 2023, our colleagues at MwRSF performed two crash tests with EVs on a standard W-beam guardrail system—the most commonly used guardrail system in the United States. The W-beam guardrail has proven to be MASH compliant through full-scale crash testing with ICE vehicles.
MwRSF tested the W-beam guardrail with a Rivian R1T pickup truck and a Tesla Model 3 passenger car, both at a nominal speed of 62 mph and an angle of 25 degrees (the MASH impact conditions for Test Level 3, the basic test level for passenger vehicles on high-speed roadways).
The Rivian pickup ruptured and broke through the W-beam guardrail system. While not unexpected because of the vehicle’s heavier weight, the ease with which it penetrated the guardrail was nevertheless startling.
The Tesla Model 3 test was even more interesting. The Tesla underrode the W-beam, which means it pushed under the guardrail, lifting it over the vehicle as the car’s momentum carried it past the system. At approximately 3,900 pounds, the weight of the Tesla is bracketed by the current MASH design test vehicles, which include a 2,400-pound passenger car and a 5,000-pound pickup truck.
At first, the failure of the guardrail with the Tesla was surprising because MASH’s testing philosophy suggests that vehicles falling within the weight range of the design vehicles should have acceptable impact performance.
It’s an interpolative rather than demonstrative assumption. However, the results of MwRSF’s impact testing challenge this conventional wisdom when it comes to EVs.
The Next Step in Testing
In June 2024, TTI conducted its own EV crash test with a stronger, more robust system: the Thrie-beam guardrail. The Thrie-beam rail element is deeper, which reduces the ground clearance by 5 inches compared to the W-beam guardrail.
We hypothesized that this might address the underride behavior observed in MwRSF’s W-beam test with the Tesla. Also, the deeper Thrie-beam has a greater cross-sectional area, meaning it’s stronger and more capable of resisting the force of impact than the W-beam. This Thrie-beam guardrail was successfully crash tested with ICE vehicles under MASH criteria, so it was a natural choice to test with EVs after the W-beam failure.
To compare with MwRSF’s findings, we performed the Thrie-beam guardrail test with a Tesla Model 3 passenger car weighing approximately 3,900 pounds. The impact speed and angle were 62 mph and 25 degrees, per MASH criteria.
Guardrail: The installation consisted of a Thrie-beam guardrail system, chosen for this next step in testing based on its enhanced strength and containment capabilities.
Vehicle: A Tesla Model 3 was used in the crash test as a representative EV model. TTI selected this vehicle based on its physical characteristics, sales volume and relevance to previous guardrail crash-testing research on EVs.
Impact: The vehicle impacted the Thrie-beam guardrail at 62 miles per hour and 25 degrees. The guardrail ruptured, allowing the vehicle to pass through the system—a failure of MASH’s test criteria. During the impact, the vehicle wedged under the guardrail, compressing its bottom edge, and ruptured and went through the Thrie-beam guardrail.
Results: When tested with ICE vehicles, the Thrie-beam guardrail system passed the industry standard evaluation criteria. However, the EV’s failure to meet these same criteria highlights the need for further research to adapt our hardware systems to accommodate the changing vehicle fleet.
The Thrie-beam’s failure when impacted by the Tesla was unexpected because the severity of the Telsa impact was within the range of current MASH crash testing.
In my nearly four-decade long career, I had never seen a Thrie-beam guardrail rupture, and it has been tested with various sizes and weights of vehicles over the years, including a commercial single unit truck and a passenger bus.
Why Did the Devices Fail?
We know many characteristics of EVs are different from its ICE counterparts, and there are certain differences that affect compatibility with roadside barriers.
The impact severity of a vehicle striking a barrier increases as its weight increases, and EVs are heavier than ICE vehicles. For example, a FORD Lightning EV pickup truck weighs about 2,000 pounds more than a conventional FORD F-150.
This increased weight places more demand on a barrier system upon impact. Understandably, a barrier near its performance limit under MASH-impact conditions can fail when impacted by heavier EVs that push it past that limit.
The center of gravity (or C.G.) height is another key difference. The weight and position of the batteries lowers the C.G. height of an EV compared to an ICE vehicle, which increases the potential for vehicle underride.
We saw this in the MwRSF test of the Tesla Model 3 impacting the W-beam guardrail, and even in the TTI test of the deeper Thrie-beam guardrail.
Crush stiffness and vehicle profile can also contribute to impact performance differences. Lack of a conventional engine compartment changes the crush profile in an EV’s front quarter panel, which interacts with a barrier system.
The lack of resistance or obstruction provided by an ICE vehicle’s engine facilitates guardrail intrusion into the vehicle’s frontal compartment, resulting in an interaction with the guardrail that can cause rail tears.
Many EVs are designed with a low, sloping frontal geometry to promote aerodynamics. This can reduce the point of contact during a crash with a guardrail system, potentially promoting underride such as that seen in MwRSF’s W-beam test and, to a lesser extent, TTI’s Thrie-beam test.
Evolving Standards
EV sales represented approximately 8% of vehicles sold last year, and according to Edmunds, the online resource for automotive inventory, there are more than 3.3 million on U.S. roads. Virta, which produces a digital EV charging platform, estimates that in 2022, 26 million EVs existed worldwide.
Industry projections reported by Investing News Network indicate the EV market share in the United States will increase to 40% by 2030, and to more than 70% by 2035. Continued growth means more opportunities for roadside crashes, which puts drivers at risk.
Roadside safety hardware must evolve to maintain the safety of the motoring public. The tests described here were only the first steps in this process. It highlight the need for more research into how EVs interact with existing infrastructure and more funds to develop new (and retrofit current) roadside safety systems for EVs.
New barrier standards also would benefit drivers of heavier ICE vehicles. Delay only invites more crash fatalities when EVs impact the infrastructure lining today’s roadways. RB
Roger Bligh is a Senior Research Engineer at the Texas A&M Transportation Institute.
