I've been wondering for years if there isnt a hidden nuance in FMVSS applicable to this situation, but admittedly I've never taken the time to read/consider further. Some PTOs are thoroughly integrated for safety - engage the PTO and it causes a fixed high-idle, touch the gas, brake, or clutch and PTO is disengaged automatically. Most PTOs tho are still dumb systems, you can drive away with them engaged so its easy for dump beds to raise without the driver noticing. Similarly, some dump beds have locking pins while others dont. As a wrecker operator and farm and log truck driver in my youth, I occasionally drove a dump or rolloff truck/trailer and always used the locking pins bc I felt they limited bounce and stiffened the chassis, but believe most professional drivers dont. Regardless, it seems like we have the technology but simply dont use it and the dump-bridge issue remains common.