It is not just around the waist.
The seat is molded so it goes up between the knees to nearly touch the bottom of the restraint. This makes it impossible to slide out of, either up or down.
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The restrictions for the ride state "When seated, one natural full leg and one natural leg that extends to edge of seat is required. No prosthetic limbs." That restriction means you cannot slide out.
I know all of this because I didn't the first time I rode and had a panic attack thinking my son, seated next to me, was going to fly out. I researched the heck out of it once I got home. I can now ride calmly and enjoy it.
And I cannot stand RNRC.