Both the Ioniq 9 and Grand Highlander have child safety locks to prevent children from opening the rear doors. The Ioniq 9 has power child safety locks, allowing the driver to activate and deactivate them from the driver's seat and to know when they're engaged. The Grand Highlander’s child locks have to be individually engaged at each rear door with a manual switch. The driver can’t know the status of the locks without opening the doors and checking them.
The Ioniq 9 has a standard front seat center airbag, which deploys between the driver and front passenger, protecting them from injuries caused by striking each other in serious side impacts. The Grand Highlander doesn’t offer front seat center airbags.
To help make backing out of a parking space safer, the Ioniq 9 has standard Rear Cross-Traffic Collision Warning with Rear Cross-Traffic Collision-Avoidance Assist, systems which detect vehicles approaching from the sides and can automatically apply the brakes to prevent a collision. Only the Grand Highlander Limited/Platinum/Nightshade offers Parking Support Brake.
Both the Ioniq 9 and the Grand Highlander have standard driver and passenger frontal airbags, front side-impact airbags, driver knee airbags, side-impact head airbags, front and rear seatbelt pretensioners, height adjustable front shoulder belts, four-wheel antilock brakes, traction control, electronic stability systems to prevent skidding, crash mitigating brakes, daytime running lights, lane departure warning systems, blind spot warning systems, rearview cameras, rear cross-path warning, driver alert monitors and available around view monitors.
The Hyundai Ioniq 9 weighs 602 to 1718 pounds more than the Toyota Grand Highlander. The NHTSA advises that heavier vehicles are much safer in collisions than their significantly lighter counterparts.