Land Transport Rule

Heavy Vehicles Amendment (No 2) 2011

Rule 31002/5

Note: This Rule should be read in conjunction with the consolidated version of Land Transport Rule: Heavy Vehicles 2004, which includes previous Rule amendments.


Objective of the Rule

Extent of consultation

Part 1     Rule requirements

Section 1     Application

Section 2     Amendments to Rule requirements

Section 3     Amendment to Schedules

Part 2     Schedule

New Schedule 4 Bolster Attachment Code

Objective of the Rule

Land Transport Rule: Heavy Vehicles Amendment (No 2) 2011 amends Land Transport Rule: Heavy Vehicles 2004 ('the Rule'). This Rule sets out requirements and standards for heavy vehicle safety. It applies to vehicles with a gross vehicle mass of more than 3500 kg.

The objective of the amendment Rule is:

Extent of consultation

For the purposes of consultation, amendments proposed to Land Transport Rule: Heavy Vehicles 2004 and 10 other Land Transport Rules were combined into a single draft Rule, Land Transport Rule: Omnibus Amendment 2011 (the draft Omnibus Amendment Rule).

On 1 June 2011, the NZ Transport Agency (NZTA) sent details of the amendment proposals by letter or email to approximately 2200 groups and individuals who had registered an interest in the Rules to be amended. The draft Omnibus Amendment Rule was made available through the NZTA Contact Centre and, together with Questions and Answers, was also made available on the NZTA's website. The availability of the draft for comment was publicised in the daily newspapers in Auckland, Hamilton, Wellington, Christchurch and Dunedin and in the New Zealand Gazette. The NZTA received 17 submissions on the draft Omnibus Amendment Rule, of which 10 commented on the proposed amendments to the Rule.

Following consultation, the provisions in the draft Omnibus Amendment Rule were split into 11 separate amendment Rules, including this Rule. The submissions that were received were taken into account in finalising this amendment Rule before it was submitted to the Minister of Transport for signing.

Part 1     Rule requirements

Section 1     Application

1.1     Title

This Rule is Land Transport Rule: Heavy Vehicles Amendment (No 2) 2011.

1.2     Date when Rule comes into force

This Rule comes into force on 1 October 2011.

1.3     Scope of Rule

This Rule amends Land Transport Rule: Heavy Vehicles 2004.

Section 2     Amendments to Rule requirements

2.1     Vehicle body and equipment attachment

Subclause 3.2(3) is amended by inserting "or Schedule 4" after "Schedule 2".

2.2     Skid plates and kingpins

Subclause 4.8(6) is amended by:

Section 3     Amendment to Schedules

3.1     New Schedule inserted

Part 3 Schedules is amended by inserting the Schedule set out in the Schedule of this Rule as Schedule 4.

Part 2     Schedule

New Schedule 4 inserted "Schedule 4 Bolster Attachment Code

(Revision 2 November 2010)


1.1     Objective

The bolster attachment system shall be designed as a total system to ensure that all loads imposed, as specified below, are reacted back to the vehicle chassis.

In particular, the Certifying Engineer shall consider all connection systems to the chassis including, but not limited to: bolts and bolt groups, twistlocks, lashings, welded fabrications, load cells, bolster pivot pins, resilient mountings and intermediate structural members. The designer shall also consider the loads the design imposes on the chassis and the bolster.

1.2     Certification life

It is expected that Design Certificates issued according to this Code should remain valid for a minimum of three years and a maximum of ten years. Samples of acceptable forms for compliance certificates are shown in the Appendix to this code.

It is permissible to use components within the bolster attachment system which may have design or service lives shorter than the life specified within the Design Certificate provided that:

Bolster attachments may be recertified at the end of their certified life where justified on the basis of assessment by a Certifying Engineer. Any repair or modification work required to extend certified life must comply with this Code of Practice.

1.3     Proprietary components

Any proprietary components used for the purpose of bolster attachment shall be rated, approved and certified by their original manufacturer, or Certifying Engineer, as being fit for that purpose according to the loading provisions of this Code.

1.4     Repairs and modifications

Repairs and modifications to the bolster attachments should be undertaken by the original manufacturer or their authorised agent.

All modifications shall be recertified by a Certifying Engineer as in 2.8.

1.5     Vehicle and bolster identification

Individual bolsters shall be stamped, indelibly labelled or marked to clearly identify their serial number.

Individual bolster mounts shall be stamped, indelibly labelled or marked to clearly identify their serial number.

At least one tag per vehicle shall be fitted identifying the bolsters, bolster attachments, bolster rating, the certifier, the manufacturer, vehicle, and expiry date compatible with the requirements of NZS 5444.


2.1     Vehicle payload

Vehicle payload shall equal the manufacturer's rated GVM minus tare, and shall not be distributed to exceed the rating on any individual component of the vehicle or vehicles.

Note: The equipment manufacturer has the right to nominate a maximum GVM less than the original vehicle manufacturer's GVM or any NZTA limitations.

2.2     Rated Bolster Load; LR

The Rated Bolster Load is the maximum payload that the bolster may carry, and shall be the greater of:

For different loading cases there may be different numbers of bolsters capable of resisting each load case specified. The bolster load shall be found by dividing by the number of bolsters resisting each loading case.

2.3     Bolster Assembly Mass; D

Bolster Assembly Mass, D shall be taken as the mass of the bolster and any other structure or securing hardware attached with the bolster.

2.4     Design Bolster Load: Static: LDS Dynamic: LDF

The Rated Bolster load calculated in 2.2 above shall be increased to allow for maldistribution within the log payload by a maldistribution of payload factor, M, for static loadings only, where

So; LDS = M x LR + D and LDF = LR + D

2.5     Loads

Where the term 'g' is used this shall be taken as g = 9.81 m/s2. All other variables or quantities shall be taken as measured in SI units unless specified.

Dynamic loads expressed in this Code are given as (Fatigue) Dynamic Load Ranges from which Fatigue Stress Ranges can be calculated and compared with allowable stress ranges.

Static loads are expressed as peak static loads in either direction (ie: up/down, left/right, tension/compression) from which peak static stresses can be calculated and compared with allowable stress levels. All loads shall be applied independently of any other design loads (ie: none shall be considered simultaneous).

Also, fatigue cycle counts in each mode of loading shall be considered independent of every other mode.

The load cycles are therefore to be counted as though no other mode of loading exists.

2.6     General design requirements

Design shall be to AS 3990 for both static and dynamic loadings or alternatively to AS 3990 for static loading and to BS 5400 PT10 or BS7608 for dynamic loading.

Guidance on allowable stresses for materials other than those permitted under these standards should be sought from reputable internationally recognised Standards.

For the dynamic condition the stress at 2 x 106 cycles is to be used (in AS3990, loading condition 3 applies), based on an expected 10-year life. Where applicable a probability of failure of 2.3% should be used. In certain cases, a higher probability of failure could be acceptable, for example, where fatigue cracking would not have serious consequences and where a crack could be easily located and repaired. It is permissible to use shorter design life or components with shorter design life provided that any such component is identified as per Section 1.2.

Where any component is likely to be damaged, worn or distorted during normal operational wear and tear, the Engineer shall select a fatigue stress level, class or category appropriate to the probable damaged condition. The Engineer shall not base allowable stress levels upon the as-new undamaged condition.

At the discretion of the Certifying Engineer a maximum service life may be specified on the Design Certificate.

2.7     Load centre

The Load Centre shall be assumed to exist at the geometric centroid of the area bounded by the bolster bed, inner faces of the stanchions and a horizontal line across the tips of the stanchions or extension pins, if fitted.

Figure 1  Determination of the load centre position

Figure 1: Determination of the load centre position

2.8     Certifying Engineer

The Certifying Engineer (HVEL category) shall be approved by the New Zealand Transport Agency on the recommendation of the Log Transport Safety Council.

2.9     Longs Bolster

Longs bolsters are designed to support logs suspended between separate towing and towed vehicles. Their mounting system allows for articulation between the vehicles.

2.10     Shorts Bolster

For the purposes of this Code, a shorts bolster is one designed to support, in conjunction with one or more other bolsters, a log packet carried on a single vehicle.

2.11     Convertible (longs/shorts) vehicle

A vehicle capable of being used in both longs and shorts operation. The bolster mounting system is able to be rapidly reconfigured to suit either mode.


3.1     Application

The static and dynamic vertical loads shall be applied as a uniformly distributed load across the top of the bolster bed, equal in total to the values specified below.

The weight of the bolster and attachments may be ignored for vertical loadings.

Figure 2  Application of vertical loads

Figure 2: Application of vertical loads

3.2     Static Vertical Load; PV

Downwards: PV = LDS x 2.5g

Upwards: PV = LDS x 0.5g

3.3     Dynamic Vertical Load Range; QV

QV = LDF x 2.0g (ie ± 1.0g)


4.1     Application

The static and dynamic transverse loads shall be applied as forces at the load centre as in Figure 3 below.

Weight due to gravity @1g may be superimposed as a uniformly distributed load (UDL) across the bolster to help resist transverse loadings.

Figure 3.  Application of transverse loads

Figure 3: Application of transverse loads

4.2     Static Transverse Load; PT (applies at the Load Centre)

PT = LDS x ± 0.5g

4.3     Dynamic Transverse Load; QT (applies at the Load Centre)

QT = LDF x 1.7g (ie. ± 0.85g)


5.1     Application

Longitudinal loading shall be checked in each of four cases

as detailed below and weight due to gravity @1g may be superimposed as a UDL across the bolster to help resist longitudinal loadings.

5.2     Static Longitudinal Loads PLF, PLR

Forwards: PLF = LDS x 1g

Applied 300mm above bolster bed height.

Rearwards: PLR = LDS x 0.5g

Applied at the bolster bed height.

Figure 4.  Application of longitudinal loads

Figure 4: Application of longitudinal loads

5.3     Dynamic Longitudinal Loads; QL1; QL2

QL1 = LDF x 2.0g (ie. ± 1.0g)

Applied at Bolster Bed Height

QL2 = LDF x 0.25g (ie. ± 0.125g)

Applied at Load Centre


The design loads specified in sections 3.0, 4.0 and 5.0 were specifically measured as being applicable to bolsters, of high torsional and bending stiffness, rigidly mounted onto a relatively flexible chassis structure.

A wide variety of configurations exists, and may expand in the future, where the connection between the bolster unit and chassis has some measure of compliance in torsion and/or linear location.

In recognition of the fact that:

The reduced dynamic loadings shall only apply to the following types of bolster attachment as defined below. Physical testing may be required to confirm compliance with these definitions.

6.1     Torsionally Independent Bolsters

Typically bolster types relying upon either gravity or resiliently restrained bolts to resist the longitudinal loads. The main connection to the chassis allows torsional displacement of the chassis rails without loading of the bolster bed through the attachment.

A minimum total of 2 degrees angular displacement between the bolster and each chassis rail in the longitudinal vertical plane (see Figure 5), with an increase in contact loads not exceeding 10kNm/degree between bolster and chassis members, shall be achieved.

Figure 5. Angular displacement requirement for torsionally independent bolster attachments.

Figure 5: Angular displacement requirement for torsionally independent bolster attachments (not to scale).

6.2     Sliding Bolsters

Bolsters mounted on sliding attachments where sufficient clearance exists to meet a minimum ± 1 degrees angular displacement (see Figure 6), with an increase in contact loads not exceeding 20 kNm/degree between bolster and chassis members.

Figure 6. Angular displacement requirement for sliding & resilient bolster attachments (not to scale).

Figure 6: Angular displacement requirement for sliding & resilient bolster attachments (not to scale).

6.3     Resiliently Mounted Bolsters

Resiliently mounted bolsters are those for which the incremental rotational stiffness does not exceed 20 kNm/degree (per attachment) for an angular displacement of ± 1 degree about the transverse axis (see Figure 6).

Typically these bolsters will be elastomeric or metal spring mounted with overriding solid connections to prevent excessive displacement.

The term "incremental stiffness" is intended to allow for preloading of resilient mounts such that static deflections under rated loads can be minimized, whilst maintaining relatively low natural frequencies at the loaded condition.

6.4     Longs and Convertible Units

Bolster mounting systems or individual bolster mounts on vehicles designed for longs or longs/shorts (convertible) operation and which are new into service after 31/3/2005 must comply with either section 6.4.1 or 6.4.2 below.

6.4.1     Type Approval

Bolster attachment systems or individual bolster mounts on longs or convertible logging vehicles may be considered to comply with this Code, provided that the manufacturer (who must also be an HVML manufacturing certifier) or an HVEL certifying engineer has evidence available for audit by the New Zealand Transport Agency that the particular design of the bolster attachments has successfully completed, on a single vehicle, 250,000 kilometres of service without any indication of cracking due to fatigue or other significant failure.

For each vehicle incorporating this design, at least one "Statement of Compliance with Type Approved Design" (see Appendix) must be signed and referred to in the Heavy Vehicle Compliance Certificate (LT400) which is issued at the time of first presentation of the vehicle for registration. Expiry date of certification is to be within the period stated in section 1.2.

6.4.2     Certification by calculation

In general, the loads specified in sections 3, 4, 5 and 6 of this Code shall be applied, with the following provisions and exceptions:

The longs bolster shall be able to rotate fore and aft about its transverse axis by at least ±5° where the incremental stiffness of the bolster attachment does not exceed 20 kNm/degree of angular displacement (see Figure 7).

Side to side rotation of the longs bolster about the longitudinal axis of the vehicle shall be limited to avoid instability.

Provision shall be made for the longs bolster to rotate about its vertical axis. This may be done utilising a standard trailer dolly ballrace turntable or slewring. The Engineer shall justify the rating of the ballrace turntable or slewring by applying the turntable manufacturer's requirements for the longs logging application using the static loadings specified in sections 3, 4 and 5 and the reduced dynamic loadings specified in 6.0.

Figure 7. Angular displacement requirement for longs bolster attachments (not to scale).

Figure 7: Angular displacement requirement for longs bolster attachments (not to scale).

In the absence of these requirements, the design bolster load, LDF shall not exceed 1.25 times the manufacturer's static vertical rating for the turntable or slewring when used on a trailer dolly.

The ballrace turntable or slewring shall be supported over at least 50% of the circumferential area of both top and bottom rings, with detailed design of the bolting being carried out by the Engineer.

Where ballrace turntables or slewrings designed for trailer dollies are not used, the loads specified in sections 3, 4, 5 and 6 of this Code shall be applied.


For some detail arrangements of bolster attachments, some bolted connections may rely on the provision and maintenance of pre-tensioned axial loads to avoid premature failure of the bolt(s) or joint. In such critical applications the manufacturer and/or Certifying Engineer shall specify and ensure the provision of:

Bolt design shall be undertaken by the following means:






All welding shall comply with AS/NZS 1554.1 or for quenched and tempered steels AS/NZS 1554.4. The required weld categories (GP, SP or FP) shall be stated on the drawings.


Where an existing primary attachment does not meet the requirements of this Code it is permissible to fit a secondary independent bolster attachment system to ensure restraint of the bolster should the primary system fail. The secondary attachment device is permissible for bolsters manufactured and fitted to vehicles before the introduction of this Code.

The secondary system shall:




Sample forms of NZTA approved acceptable design certificates.

Land Transport Rule - Heavy Vehicles Amendment (No 2) 2011 - Rule 31002/5
NZ Transport Agency, Waka Kotahi