Its a sort of complex issue though. Buses don't have to meet the same standards are other vehicles for example. And you will never be able to incorporate air bags.
From a safety perspective, you need a seat mount that can carry and absorb the load in the crash without flipping forward/backward. That is simple enough to test with a static pull. Airline seats up until the early 2000s used the same approach for certification.
The other major concern is integrity of the box. It needs to survive a rollover without crushing the occupants. Though there are plenty of vehicles sold with marginal rollover safety.
Finally the design needs to be such that cabinets can't open when deformed by crash loads, ejecting contents. All heavy objects need to be contained, as a 25lb inverter or 100lb water tank can kill just an easily. This is less of a risk with bigger vehicles, as due to their mass, they simply don't have the same deceleration G loading.