Also note that this is not a HPDE Track Day regulation but is wise advice from the Drift supplementary regulations:
Restraint Systems/Seat Belts and Seats
WARNING: The use of 4/5/6 point belts in a vehicle without a full roll cage can result in serious injury in the event of a rollover. When used in a vehicle without a full roll cage, the design of these systems does not allow side/downward movement of the head and shoulders and thereby exposes the head and neck to impact from a collapsed roof. The use of a 5 or 6-point belt systems in a car equipped with a roll cage is mandatory. NOTE: Refer to “1.3 ROLLOVER PROTECTION – ROLL BARS AND CAGES” in these Supplementary Regulations for a definition of the different types of rollover protection.: Add the following chart, regarding the relationship between harnesses/belts and the type of rollover protection fitted to the vehicle:
*Breakaway and ASM shoulder straps are designed to release or tear away in the event of a frontal impact. The Anti-Submarining (ASM) shoulder belt typically consists of the inboard shoulder belt being fitted with a mechanism that releases an additional loop of webbing to allow the upper torso to twist and move forward in the event of a frontal impact. This, in effect, prevents sliding under the belt and also allows the head of the driver to move away from a collapsed roof in the event of a rollover.