MiradaAcres - 10/8/2024 12:03

571.121 S5.6 Parking Brakes

571.121 S5.6(c)
At the option of the manufacturer, the trailer portion of any agricultural commodity trailer, heavy hauler trailer, or pulpwood trailer may meet the requirements of § 393.43 of this title instead of the requirements of S5.6(a).

A detach/RGN falls under 571.121 S5.6(c) and is exempt from parking brakes if is meets requirements for 393.43 Breakaway and emergency braking.  The trailer has common diaphragm brakes, the emergency/relay valve applies the brakes when supply line pressure drops via the trailer reservoice and also applies with service line applicaiton from the supply reservoir.  This has nothing to do with old vs new trailer.