School bus drivers are surrounded by driver airbags while they’re on their way to and from work. So, it’s fair to ask: why aren’t frontal airbags in school buses, too?

The simple answer? A car airbag just can’t be easily installed into a school bus. It takes an enormous amount of engineering. While it might sound like a simple upgrade, airbags are not one-size-fits-all. Every airbag system is finely tuned to the vehicle it’s installed in, from the size and shape of the vehicle to how fast it typically moves, even to how the seat and steering wheel are designed. Installing a system that wasn’t made for a school bus just wouldn’t work.

That’s where 4Front comes in. 4Front by IMMI is specifically designed to give drivers extra protection during serious frontal crashes, specifically the kind of crash that would be severe enough to set off an airbag. Industries that already use frontal airbag protection have seen first-hand how this advanced safety system can save lives. Whether in a fire truck rushing to an emergency or a heavy-duty semi-truck crossing the country, IMMI’s 4Front airbags have helped protect drivers from serious injuries in the worst crashes. And now, that same safety technology is available to protect school bus drivers.

What Actually Goes into a School Bus Airbag?

Before any actual crash testing ever happens, IMMI engineers and crash safety experts spend 18-24 months developing and validating a new airbag system for school buses. That time is spent running through multiples stages of development including work like:

• Simulation Testing: Computer modeling plays a critical role in the early stages of airbag system development. These simulations allow engineers to predict how a school bus and its driver would respond during a variety of frontal crash scenarios. By analyzing these virtual crash events, engineers can evaluate potential injuries, study how the body moves during impact, and fine-tune the design of the airbag system accordingly. This approach enables IMMI to test and improve safety performance efficiently, reducing the number of full vehicle crashes required, saving time and resources, and helping to ensure that the final system offers the best possible protection when deployed in the real world.
• Sled Testing: Before a full school bus is ever crash tested, several tests are run using a specialized setup called a sled test. This test uses real bus parts, like the actual driver seat, seat belt, steering column, and steering wheel, mounted to a platform that simulates a crash. There are normally 3 to 5 runs to figure out the exact speeds where the airbag should or should not deploy. These are called “no fire” (airbag does not go off) and “must fire” (airbag does go off) speeds. Important things to look at during these tests are injury numbers and how the body moves (kinematics) to make sure the system protects the driver correctly. The test setup, or “sled buck,” is built by CAPE, the Center for Advanced Product Evaluation, IMMI’s own crash test and safety engineering partner.
• Resonance Testing: Not every part of a school bus is an ideal location for a crash sensor. To ensure accurate performance, various mounting positions are tested to identify the most reliable spots for detecting impact. This process, known as resonance testing, helps confirm that the sensor can distinguish between a true crash event and normal road vibrations. Proper sensor placement is critical to ensure the airbag system deploys only when necessary, contributing to a dependable and effective safety system.
• Barrier Testing: Now that all the simulations, initial sled tests run, and sensors mounted in the correct places, it’s time to crash a school bus! As part of the final validation process, barrier crash testing is conducted at CAPE to confirm the airbag system performs as intended in a variety of real-world crash conditions. Multiple barrier types are used to simulate different crash scenarios. Additional tests include the bus hitting the barrier at different angles (not just a head-on collision), to confirm that deployment occurs only in severe frontal crashes. Each test helps confirm that the 4Front airbag system responds the right way in serious crashes, giving drivers the protection they need, only when it’s needed.

This wraps up development for the airbag program for the school bus.

What Can You Do?

If you’re interested in learning more about 4Front airbags to better protect your drivers, here are a few steps you can take:

• Learn more about 4Front
• Get further information on CAPE’s crashes and capabilities
• Watch a CAPE-led school bus crash demonstration highlighting 4Front in action here:

• Talk to your transportation director about IMMI’s 4Front system
• Contact your bus dealer or IMMI

Every driver deserves to go home safely. Let’s make sure all school bus drivers are protected, too.

Built to Work with Lap-Shoulder Belts

4Front is also designed to work hand-in-hand with another proven safety technology: lap-shoulder belts. More school buses are now being built with these belts because they help keep drivers and students securely in place during a crash, reducing the risk of serious injuries. When used together, lap-shoulder belts and 4Front airbags create a layered safety system that protects the driver from both initial and secondary impacts. If your bus has lap-shoulder belts, you’re already one step ahead. 4Front helps take it even further.

For more than 60 years, IMMI has been a leader in advancing occupant safety across transportation industries. From school buses and commercial trucks to ambulances and fire apparatuses, IMMI designs and manufactures safety systems trusted by OEMs and fleets around the world. With a deep focus on real-world protection and rigorous testing, IMMI has led the way in setting industry standards for seat belts, child seating, and advanced restraint technologies.

The views expressed are those of the content sponsor and do not reflect those of School Transportation News.

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