This picture is from the Kilimanjaro Safari, which has tie down hooks similar to the buses. I put it here for illustration.
My daughter's power and manual wheelchairs both are designed for transit with tie down loops on the front and back. Green circle on the photo shows one of the back ones; there is one on each side, back and front. I marked them with bright colored tape, so I can tell the driver to look for that. Most are appreciative.
Both her wheelchairs are even crash tested. Since she can't stand or sit securely on a bus seat, she does stay in her wheelchair because it's safer for her situation.
I watch the tie down like a hawk because I have occasionally found the driver to be attaching the hooks someplace they shouldn't be - for example on the rigidizer bar or canes marked with red X. Pretty much always, the driver is happy when I point it out.
We had one time when the driver refused; he argued that doing it up higher was 'safer' and refused to move it. I said if he wasn't going to move it to the correct spot, he needed to let us off the bus.
We ended up getting off his bus and calling Transportation to put in a complaint
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