Dont understand the "Danger Air Brakes" bumper sticker at reply #28.
Air brakes Dangerous? Since when
Using Air brakes downhill in the Alps for example the follower does not see a brake light, that's probably why (at least back then?) I am no trucker:-)
On a straight truck, function of the brakes air or hydraulic, or even the combination of, still generally requires actuation of the foot pedal, and with this one should enact the electrical brake light circuit luminating the bulb(s), always, at least if all is well.
As far as the signage declaring that the vehicle is equipped with air brakes and potential danger, I believe it is intended to serve as a notice to those with involvement of the vehicles' functioning as there are unique concerns for such verses the hydraulic or mechanical systems, and not all persons may be permitted to operate the vehicle equipped as such.
An example: say the operator of the vehicle jumps in the drivers seat, after a long duration of stoppage, this permitting the air pressure to be lost, starts the engine and places the vehicle in motion prior to permitting a duration of time to pass permitting the air system to regain sufficient pressure, there will be no brakes! My M911 Oshkosh Military Tractor addresses this issue by making the throttle pedal to fuel injection pump (diesel) an air operated function, therefore: no air, no throttle.
Or perhaps to remind the operator that excessive repetitive actuation of the air brakes may tax the delivery rate from the air compressor hence draining the air volume and therefore pressure leading to loss of brake function; this being evident in city traffic congestion, or perhaps long down hill runs, both where the operator would be on and off the brakes and the engine R.P.M.s may be low thereby reducing the pumping rate for the compressor and air supply delivery.
And then maybe as a reminder that when parked, engine off, in the early years of air brakes, you might "set" your brakes and walk away, but when the air pressure bleeds down the brakes will release, as "spring-lock" air cans were developed later. What this vehicle is equipped with I have no idea, but one should always "set" the mechanical parking brake or chock the wheels when the vehicle is unattended, to avoid surprises upon returning to where one thought, they left their vehicle otherwise.
Generally, particular training is required for the operators of air brake equipped vehicles to address these and other concerns unique to it's operation; that meaning that the sign might really be saying: if your not trained and certified to operate vehicles equipped with air brakes, stay away, as otherwise you present a danger to yourself and others!
Scott.