Proposal to amend para. 2.8 of Annex 8 to UN R13 to require trailers utilizing service braking system energy reserves to fulfil one of three requirements when uncoupled and park brake control released: pressure in spring brake compression chamber shall reduce to 0 kPa when energy reserves reduce to 280 kPa, pressure reduction in service braking system energy reserve results in corresponding reduction in spring compression chamber pressure, or combined service and parking braking forces shall hold laden trailer as required when service brake energy reservoir reduces from 850 kPa to 0 kPa.