Hyundai Mobis has developed Active Rear Safety Control. When a trailing vehicle follows dangerously close at highway speeds, the system first warns the driver, then automatically increases speed to secure a safe distance. It enables predictive defensive driving against rear traffic. Senior research engineer Jun-young Lee and research engineer In-hyuk Seo from the Driving Advanced Logic Design Team gave us the inside story.
The spark came from Hyundai Motor Group’s idea competition in 2022. The concept drew inspiration from existing ADAS functions that rely on sensors to monitor the road ahead. This fresh approach—focusing on rear traffic—earned top honors in the contest, setting the stage for development.
What made this idea stand out was that it didn’t require any additional sensors. By leveraging only existing ADAS radars and cameras, the team was able to shorten development time dramatically. As senior research engineer Jun-young Lee explains:
“Even though we’re an advanced R&D group, we believe advanced tech should never drift too far from production reality. We focused on innovations that can go straight into mass production, which is why we built this system on sensors already being used in vehicles.”
Until now, rear crash-prevention technologies in the market mostly consisted of warnings and pre-crash seatbelt tightening. Hyundai Mobis’ solution goes a step further, autonomously adjusting the gap between the lead car and trailing vehicle to avoid risk altogether—a major leap in autonomous control.
The system engages when Smart Cruise Control is active on the highway. If a trailing car follows within 10 meters, the driver receives both visual and audible warnings. If the situation persists, the vehicle automatically accelerates to reestablish safe distance. Side radars on the rear bumper track the approaching vehicle, while the forward-facing camera identifies lanes and the lead car to ensure the acceleration maneuver is safe.
It sounds simple—speeding up slightly to escape a tailgater—but implementing it safely required a host of considerations, from traffic laws to countless real-world driving variables. Research engineer In-hyuk Seo explains:
“The system only begins acceleration if a trailing car maintains a dangerously close distance for more than 5 seconds. Acceleration is capped to the posted speed limit, and the following distance never goes below Smart Cruise’s minimum Level 1 setting. If the driver set the following gap at Level 2, the system only uses the unused margin down to Level 1. That way, safety remains the priority.”
Just as important, the system uses sensors already present on production cars. Distance from the rear vehicle is measured using Hyundai Mobis’ Corner Radar MAR130, which also powers Blind-Spot Collision Avoidance (BCA), Rear Cross-Traffic Collision Avoidance (RCCA), and Safe Exit Assist (SEA).
The real trick was identifying whether the trailing car is in the same lane. Adding new sensors would have been easier, but the team held firm to their principle of maximizing existing equipment. Instead, they turned to the front camera.
“Detecting a car behind with corner radar is easy. But figuring out if it’s approaching in your lane requires knowing the lane shape. Since the rear lane is essentially the road you just passed, we realized we could use front camera data. That gives us about four seconds of rear-lane information—one of the core breakthroughs of this system.”
Research engineer In-hyuk Seo shared his perspective. “At 100 km/h, this system can read the lane behind for about 110 meters, which means it can spot an approaching car early. But if you warn the driver too soon, it just leads to fatigue. That’s why the system constantly monitors the rear vehicle and only issues a warning when the time-to-collision (TTC) shrinks to a critical threshold.”
Seo also explained that Active Rear Safety Control makes its decisions not just on relative speed but also on distance. “If the trailing car slows down and starts tailing closely, the relative speed difference drops, so in that case the system switches to distance-based judgment. If your car is within the distance that the trailing vehicle can cover in about 0.38 seconds, the driver gets a warning. And if that risk continues for more than 5 seconds, the system initiates acceleration control. For example, if the trailing vehicle is traveling at 100 km/h, that’s about 27.8 meters per second—so the warning kicks in once it comes within roughly 10.5 meters.”
Active Rear Safety Control is a prime example of the “fusion” power Hyundai Mobis is betting on. Creating something new out of existing technologies requires broad expertise and know-how. Hyundai Mobis has specialists across software, semiconductors, integrated control, and E/E (electrical/electronic) architecture. That depth of talent makes it possible to fuse different technologies into real mobility innovation.
As public awareness grows around defensive driving against tailgaters, Hyundai Mobis is already pitching this system to domestic and global automakers for mass production. Because it works without changing the fundamental ADAS setup, leading carmakers worldwide are showing strong interest.
And Mobis isn’t stopping here. The next stage of Active Rear Safety Control expands the scope of autonomy even further: after acceleration, the system will automatically change lanes to escape risky situations. Once in production, this upgrade could make the driving experience even safer. The two engineers explained further:
“We planned Active Rear Safety Control as a phased rollout. First, functions that can be realized with the standard sensor set. Then, for different models and trims, we’ll add more features that match additional sensors. For example, lane-change capability requires front corner radars. On vehicles equipped with those, both acceleration control and automated lane change will be possible. In short, the technology expands feature by feature depending on the hardware installed.”
As a mobility platform provider, Hyundai Mobis delivers modular technologies as integrated solutions tailored to customer needs. The company’s mission is to safeguard users, provide comfort, protect the environment, and help shape a new mobility ecosystem. It’s a vision for safer, smarter mobility—and one we can all get behind.
Photography by Hyuk-soo Cho
HMG Journal Operation Team
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