On large buses, it is common for the low air pressure warning devices to signal at a higher pressure than the standard below-55-psi threshold used on most air-brake vehicles. What is that typical range?

AAMVA CDL Manual, Section 5, subsection 5.1.11 (p. 5-3), 'Low Air Pressure Warning'

Large buses often carry more passengers and may have different air system designs, so manufacturers set an earlier, higher-pressure warning point to give drivers more margin before a problem becomes critical. Recognizing that the exact threshold can vary by vehicle type keeps you from assuming every warning light behaves identically.