What measurement is crucial for a bus driver to monitor for safe operation?

Monitoring air pressure is crucial for a bus driver to ensure safe operation. The air pressure in the bus's braking system is critical for effective braking. A properly maintained air pressure level is essential for the air brake system to function correctly, as it ensures that the brakes engage and disengage effectively. Insufficient air pressure can lead to brake failure or reduced braking capability, which poses a significant safety risk not only to the driver and passengers but also to other road users.

In comparison, while oil temperature, transmission fluid level, and brake light intensity are important factors in vehicle maintenance, they do not have the same immediate impact on the safety and operational capability of the bus as air pressure does when it comes to braking systems. For instance, low oil temperature can affect engine performance, and the transmission fluid level is important for gear functionality, but neither directly influences the bus's ability to stop quickly and safely. Similarly, while brake lights are essential for signaling to other drivers when a bus is stopping, they do not directly affect the mechanical ability of the brakes to function effectively. Thus, monitoring air pressure is key to the safety and operational readiness of the bus.