Let's look at the wheelchair wildly careening down the hill because the caregiver's hand accidently slipped. There is a solution, and it's surprising no one thought of it before.
It's as simple as customizing a wheelchair with bicycle brakes so the pusher has control. Veech Breakwell received an inventor's award, and he expects to have brake kits available for sale before too long.
But not so fast! Read the comments where a former caregiver and potential wheeler voices his objections to that method of managing an occupied wheelchair on an incline. At any rate, be careful wheelers, when traveling in hilly terrain!