PBS Directional Stability Under Braking Transitional Arrangements Discussion Paper

Consultation closed Friday 12 February 2021. We would like to thank everyone who took the time to provide feedback.

What is it?

The purpose of the Directional Stability Under Braking (DSUB) Standard is to manage the safety risk of vehicle instability when braking in a turn or on pavement cross slopes. A vehicle must not exhibit gross wheel lock-up behaviour in any loading condition and must remain in a straight lane of width equal to that specified in the standard Tracking Ability on a Straight Path for the corresponding level of operation when it is braked from 60 km/h. Compliance with this Standard is currently achieved through ‘deemed to comply' provisions (e.g. a vehicle that has a functioning anti-lock or a load proportioning brake system that effectively prevents gross wheel lock-up on each axle group is deemed to comply with the Standard).


The endorsement of the National Transport Commission’s PBS Marketplace project outlined four recommendations, one of which was for the NHVR to complete a review of the PBS Standards. To deliver on this recommendation the NHVR commenced the PBS Review Project and contracted consultant Dr John de Pont from TERNZ Transport Research Ltd (TERNZ Transport), to undertake a review of the first three standards, including the Directional Stability Under Braking performance requirements. The NHVR has undertaken consultation, meetings and workshops with industry and jurisdictions to obtain feedback throughout the development of the Standard.

The NHVR is delivering the recommended amendments to this Standard and the recommendations from TERNZ Transport and industry, along with a set of transitional arrangements to manage the impact the change may have on the existing PBS fleet.

Why we’re consulting

In order to provide industry and affected stakeholders with sufficient time to make required business changes as a result of the DSUB Standard amendments, the NHVR is proposing to use a staged approach to the implementation. The NHVR has committed to giving industry the opportunity to provide input to these arrangements prior to implementation.

Key document