Engineering Safer EV Structures: The Next Frontier in Body-in-White Design

A Global Call for Safer Vehicle Structures

With 69 million electric vehicles (EVs) now on the world’s roads in mid-2025, and annual EV sales racing toward 22 million units this year, the automotive landscape is witnessing a profound shift. At the same time, the World Health Organization reports 1.19 million annual traffic fatalities worldwide and up to 50 million injuries each year. Side-intrusion crashes remain especially deadly, with 46,000 road deaths recorded in the U.S. alone in 2022.

For EVs, the stakes are even higher. Unlike an internal combustion engine (ICE) car, where the relatively small fuel tank can deform without catastrophic consequences, an EV’s massive battery pack—often weighing around half a ton—sits under the floor and cannot tolerate intrusion. A punctured cell can trigger a thermal runaway event, turning what should be a survivable crash into a life-threatening fire. While the rise in EV numbers often dominates discussions of sustainability and energy efficiency, ensuring safety remains paramount and poses many technical challenges for engineers.

What Exactly is the Body in White (BIW)?

The BIW is the complex structural framework of stamped metal panels, beams, reinforcements, and welded joints that form the foundation of the vehicle. It’s a hidden skeleton that largely decides whether a car will protect its occupants in a crash. It is the “safety shield” for passengers—and now for the battery pack too. When the unavoidable happens, the BIW is the last line of defense after all “active safety measures” fail to avoid the crash.

I’ve spent over 25 years designing these structures for passenger vehicles, and I can tell you this:
If the BIW is not robust, everything else—safety, handling, and durability—is compromised.

Key functions of the BIW:

1. Crash Energy Management – Directs and absorbs crash forces to protect the occupants.
2. Structural Stiffness – Ensures predictable handling, reduced noise, and durability.
3. Platform Integration – Supports drivetrain, suspension, battery packs (in EVs), and interior fitment. Almost everything is mounted to the BIW structure.
4. Weight Efficiency – Balances strength and lightness to improve fuel economy or EV range.

FIG. 1 – Body in White Structure of a passenger vehicle

Global Safety Regulatory Landscape that Shapes BIW Design

Safety standards are evolving rapidly to reflect the risks of heavier EVs with large underfloor batteries. In the U.S., FMVSS 214 defines stringent side-impact protection, while FMVSS 305a now requires that after any crash, no electrolyte leakage occurs, no fire ignites for at least five minutes, and the battery remains electrically isolated (>60 ohms/volt).

The IIHS updated side crash test now uses a 1,900 kg barrier striking at 60 km/h, simulating modern SUVs. Euro NCAP protocols penalize deformation around the battery pack, while Bharat NCAP, launched in 2023, has begun driving similar advances in India.

When I was part of the Mahindra BEV program, these requirements were very real constraints. The vehicle was designed not only to achieve Bharat NCAP’s top rating but also to pass export homologations. Aligning the same structure to meet global crash norms requires a delicate balancing act. For example, side-pole impact requirements in Euro NCAP and Latin NCAP pushed for additional reinforcements, while FMVSS frontal offset criteria demanded optimized energy absorption at the front crush cans.

Such multi-standard compliance has now become the norm in global platform design. Meeting these global standards requires precise BIW load-path engineering, particularly around the rockers and front rails, where crash energy must be absorbed before reaching the battery and occupants.

BIW Design Strategies for Occupant and Battery Safety in EVs

As discussed above, regulatory frameworks impose stringent requirements, while EV architecture introduces new dynamics. The battery pack adds considerable weight, shifts the center of gravity, and creates a “no-compromise” safety zone. Here are the BIW strategies that worked for me and their significance in EV design:

1. Side Sill (Rocker) Reinforcements

The side sill, or rocker, is one of the most critical structures in an EV. In side-pole (T-bone) crashes, intrusions can puncture the battery, creating risks of thermal runaway. Research shows that extruded aluminum side sills (EN AW-6082 T6) can absorb up to 40% more crash energy than steel, though they come with significant cost penalties.

In practice, I’ve found that multi-cell UHSS roll-formed sills can offer nearly the same crash performance with only a 5–8% mass penalty and much lower cost, making them an ideal solution for high-volume EV programs.

2. Front Rails and Crush Cans

FMVSS 208 frontal crash tests and Euro NCAP offset frontal tests put immense demand on front crash structures. For EVs, the BIW must hold a 600 kg battery pack while still folding gracefully in a crash. Unlike traditional vehicles, engineers can’t run a driveshaft tunnel through the middle of the BIW for strength and energy absorption.

Instead, by designing three-stage deformation zones, we were able to reduce peak deceleration forces by almost 25% in CAE simulations, ensuring compliance with IIHS injury criteria while protecting the EV battery from high g-force transmission.

The welded or bolted crush cans absorb energy in low-to-medium speed impacts and prevent direct load transfer into the battery pack’s front edge by acting as a sacrificial structure. In recent BEV programs I worked on, we adopted splayed front rail designs with a unique three-point buckling strategy. This enabled three-dimensional staged distortion of the rail for maximum energy absorption.

3. Roof Crush and Rollover Protection

FMVSS 216 roof crush resistance requires that roofs withstand three times the vehicle’s weight. With heavier EVs, BIW teams can’t afford to cut corners. Advanced hot-stamped boron steel reinforcements in the A- and B-pillars distribute rollover loads. The front headers and roof bows, along with the B-pillar, also play a significant role in absorbing roof crush loads, which simulate rollover incidents often seen on highways.

I’ve seen this save precious cabin space in test sleds where battery packs remained untouched.

4. Seamless Load Path is the Key

Although the individual strength and design of critical BIW components like the side sill and front rail are essential, the holistic approach of seamless load-path design is paramount for achieving structural efficiency in EVs.

Rather than each component acting in isolation, they must work together as an integrated system to channel crash energy smoothly from the front crush can, through the side sill, and onward to the rear long members. This continuous and uninterrupted load path ensures that impact forces are absorbed and dispersed over the entire structure in a controlled manner.

For EVs, where protecting heavy battery assemblies beneath the floor is critical, a seamless load path reduces the risk of intrusion and catastrophic battery breaches.

FIG. 2 – Load paths of a typical EV Body in White 

5. Newer Trends: Structural Battery Packs

Tesla and some leading Chinese OEMs have pioneered the use of structural battery packs that replace traditional floor panels with the battery pack itself, forming a critical part of the vehicle’s load-bearing structure.

This innovation integrates the battery cells directly into the vehicle’s frame, creating a single, rigid unit that improves overall structural stiffness but introduces engineering challenges for BIW design. The BIW must now be intricately designed around the battery’s rigid shape, requiring new strategies for crash energy absorption and protection, especially in side impacts and underfloor intrusion scenarios.

Repairability and safety standards also become more complex because any damage to the structural battery pack can affect both the vehicle’s integrity and battery safety.

FIG. 3 – Tesla Model Y Structural Battery Pack

6. Use of Advanced Materials

Beyond geometry, the choice of materials plays a crucial role in overall BIW strength and energy absorption efficiency. High-strength hot-formed boron steels have become indispensable in critical sidewall components such as the A-pillar, B-pillar, and outer rocker panels due to their exceptional tensile strength and crash resilience.

These materials enable slimming down components without sacrificing safety, providing superior intrusion resistance during side impacts. Meanwhile, aluminum alloys are often employed inside rocker reinforcements, offering a lightweight solution that complements the boron steel outer shell.

For underbody elements like the front and rear long rails, dash panels, and floor cross members, we frequently use dual-phase (DP) grades or ultra-high-strength steel (UHSS), which combine high strength with excellent energy absorption ability.

These carefully selected materials and their strategic placement within the BIW architecture ensure optimal crash performance by minimizing deformation and intrusion, thereby protecting both the occupants and sensitive components like battery packs in EVs. Some Chinese automakers claim they are using around 90% high-strength steel (HSS), while most OEMs use around 60% by weight.

FIG. 4 – Xiaomi  YU7 Mixed Material Strategy

Emergence of AI and Computational Intelligence in EV Safety

The rise of advanced computational methods—especially AI-driven topology optimization—is accelerating innovation in BIW safety. Traditional finite element crash simulations remain essential, but AI-based approaches can suggest novel load paths and reinforcement strategies that human intuition may miss.

Many startups are entering this space with optimization tools. Companies such as Nature Architects and Dassault have developed software that automatically evolves BIW geometries for crash energy management once we define the design space and target KPIs. They consistently identify optimized areas—branched rocker geometries or hollow cross-sections—that improve stiffness and energy absorption while cutting weight.

In one recent study, my team leveraged AI-enhanced optimization to redesign a rocker section. The output revealed unconventional ribbing layouts that improved crash energy management by 12% while reducing mass by nearly 8%. Integrating such design intelligence early in the product cycle is now becoming a competitive necessity.

The next logical evolution of AI will be linking BIW to driver-assistance tech. In the near future, we will see ADAS data feeding back into BIW design loops, creating structures optimized for real-world crash behavior rather than only lab tests.

FIG. 5 – Bracket and Reinforcement Design optimization using AI tools 

The Path Forward

We can celebrate advancements in ADAS, solid-state batteries, or predictive AI. But when metal meets concrete, it is the BIW that decides who walks away. No airbags or driver-assist technologies can make up for a weak body structure.

The United Nations has called for halving global road deaths by 2030. That may appear idealistic, but each innovation in BIW design brings us closer. For EVs, this means designing reinforced sills that resist pole intrusions. It means multi-stage crush cans and rails that deform in a predictable manner. It means roofs and pillars that preserve cabin space even under a rollover.

It also means smarter use of steel, aluminum, and composites, guided by AI tools that cut weight without cutting safety. All are tangible steps toward vehicles that not only survive crashes but prevent fatalities.

As EVs become mainstream, the fusion of occupant and battery safety through optimized BIW design will be the deciding factor in achieving the UN’s 2030 target.

As body-structure engineers, we are not just responding to regulations—we are shaping the very confidence with which society embraces sustainable mobility. With the rise of EVs, autonomous vehicles, and advanced materials, BIW design will continue to evolve rapidly.

By embedding innovation at the heart of BIW design, the next generation of EVs will not only be greener but also demonstrably safer.

So, the next time you step into a car, remember—your safety starts long before the paint dries.

Author Biodata:

Prasad Kulkarni is Manager – Body Structures Engineering at Mahindra Integrated Business Solutions (formerly Mahindra Automotive North America), with over 25 years of global experience in Body-in-White (BIW) structural design. His expertise spans crashworthiness, lightweighting, and advanced manufacturing for passenger vehicles battery electric platforms.

He has led programs across the complete vehicle development cycle with a strong focus on occupant protection and EV safety. His work has supported platforms aligned with Bharat NCAP, Euro NCAP, and FMVSS standards, pioneering the use of hot-stamped steels, aluminum, and AI-driven optimization for safer, lighter, and sustainable vehicle architectures.

Alongside his professional work, Prasad mentors the next generation of engineers by conducting STEM sessions for students, channeling their interest in design engineering and real-world applications, and guiding them toward careers in automotive engineering through STEM education.

An internationally recognized expert, he remains passionate about advancing crash-safe, sustainable mobility and sharing insights with the global engineering community