4. The driver
The driver is the most important safety item on the bus.
Explanation:
In every vehicle, the driver is the most important safety item. And for the bus, here too!
The driver has to drive the bus safely and operate all the other equipment. If anything happens to the driver, the safety & security of vehicle and passengers will be in danger.
So, out of anything, the driver safety is utmost important. And, the driver is the most important safety item on the bus.