I try to avoid it, but it happened anyway: on my cycle-commute I got stuck alongside a city bus at a red light. Inevitably, the bus did its air brake thing right next to my ear: PSSSSSSSSSSSSSSSSSHHHHHT!
The deafening sound of air brakes releasing is frustrating because it is simultaneously painful and trivially avoidable. For literally a few extra dollars, heavy vehicle manufacturers could install a muffler on the brake exhaust valve, easily cutting the sound level by 30 dB (perceptually speaking, about 1/8 as loud). But they choose not to. Thus air brakes continue their assault on our senses.
Good design, they say in 2019, should always consider the environment. That environment includes the air we breathe and the sounds we hear–not just for the owners or operators of equipment, but for those who coexist with them. Designers of city vehicles who specify air brakes that emit sounds above the pain threshold deserve a special place in hell alongside the inventors of backup beepers and gas-powered leaf blowers.