DRAFT  Australian Design Rule 3 8/05 Trailer  Brake Systems   1 
 
 
 
  
Vehicle Standard (Australian Design Rule  38/05 – 
Trailer Brake Systems ) 2018  
I, PAUL FLETCHER, Minister for Urban Infrastructure, determine this vehicle standard under section 7 of the Motor Vehicle Standards Act 1989.     Dated      2018 
             
Paul Fletcher  [DRAFT NOT FOR SIGNATURE]  
  
Minister for Urban Infrastructur e
 DRAFT  Australian Design Rule 38/05 Trailer  Brake Systems  2 
 
   
  
CONTENTS  
 
1. LEGISLATIVE PROVISIO NS .......................................................................... 3  
2. FUNCTION  ........................................................................................................ 3  
3. APPLICABILITY  .............................................................................................. 3  
4. DEFINITIONS  ................................................................................................... 5  
5. DESIGN REQU IREMENTS FOR TRAILER S UP TO 4.5 TONNES ‘ATM’  . 5 
6. GENERAL DESIGN REQUI REMENTS FOR TRAILERS  OVER 4.5 
TONNES ‘ATM’  ................................................................................................ 5  
7. SERVICE BRAKE SYSTEM  ............................................................................ 8  
8. EMERGENCY BRAKE SYST EM .................................................................. 12  
9. PARKING BRAKE SYSTEM  ......................................................................... 12  
10. GENERAL PERFORMANCE ROAD TEST CONDITIONS  ........................ 13  
11. SERVICE BRAKE EFFECT IVENESS TEST CONDITIONS  ....................... 14  
12. DOG TRAILER FRICTION UTILISATION  .................................................. 15  
13. SERVICE BRAKE FADE EFFECTIVENESS TEST ..................................... 15  
14. EMERGENCY BRAKE SYST EM EFFECTIVENESS TES T ....................... 16  
15. PARKING BRAKE EFFECT IVENESS TEST ............................................... 16  
16. TIME RESPONSE MEASUREMENT ............................................................ 17  
17. SERVICE BRAKE EFFECT IVENESS CALCULATION  ............................. 19  
18. SERVICE BRAKE FADE C ALCULATION  .................................................. 21  
19. EMERGENCY BRAKE SYSTEM CALCULATION.  ................................... 21  
20. PARKING BRAKE CALCULATION  ............................................................ 21  
21. TIME RESPONSE  ........................................................................................... 22  
22. SPECIFICATION OF BRA KE SYSTEM COMPONENTS  ........................... 22  
23. ALTERNATIVE STANDARDS ..................................................................... 26  
APPENDIX 1  ................................................................................................................. 33  
APPENDIX 2  ................................................................................................................. 35  
APPENDIX 3  ................................................................................................................. 36  
APPENDIX 4  ................................................................................................................. 38  
   DRAFT  Australian Design Rule 38/05 Trailer  Brake Systems  3 
 
   
 1. LEGISLATIVE PROVISIONS  
1.1. Name o f Standard  
1.1.1. This Standard is the Vehicle Standard (Australian Design Rule 
38/05 – Trailer Brake Systems ) 2018. 
1.1.2. This Standard may also be cited as Australian Design Rule 38/05 — Trailer Brake Systems . 
1.2. Commencement  
1.2.1. This Standard commences on the day after it is registered.  
2. FUNCTION 
2.1. The function of this vehicle standard is to specif y requirements for 
braking  of traile rs under both normal operating and emergency 
conditions. 
2.2. Compliance can be demonstrated by road testing and/or calculations based on data for ‘ Approved’ components. 
3. APPLICABILITY  
3.1. This standard applies to category T vehicles 
with a ‘ Gross Trailer Mass’ 
exceeding 750 kg from the dates set out in clauses 3.1.1 to  3.1.2 and the 
table under clause 3.3 below  (except those trailers designed for use 
behind a drawing vehicle with a maximum speed less than 50 km/h). 
3.1.1. 1 [July 2019]  for all new model vehicles.  
3.1.2. 1 [November 2019]  for all vehicles.  
3.2. For the purposes of clause 3.1 a "new model" is a vehicle model first produced with a 'Date of manufacture' on or after the agreed date in clause 3.1.1.   DRAFT  Australian Design Rule 38/05 Trailer  Brake Systems  4 
 
   
 3.3. Applicability Table  
Vehicle Category  ADR 
Category Code * UNECE Category Code *  Manufactured on or After  Acceptable Prior Rules  
Moped 2 wheels  LA L1 not applicable   
Moped 3 wheels  LB L2 not applicable   
Motor cycle  LC L3 not applicable   
Motor cycle and sidecar  LD L4 not applicable   
Motor tricycle  LE L5 not applicable   
Passenger car  MA M1 not applicable   
Forward -control passenger vehicle  MB M1 not applicable   
Off-road passenger vehicle  MC M1 not applicable   
Light omnibus  MD M2 not applicable   
Heavy omnibus  ME M3 not applicable   
Light goods vehicle  NA N1 not applicable   
Medium goods vehicle  NB N2 not applicable   
Heavy goods vehicle  NC N3 not applicable   
Very light trailer  TA O1 not applicable   
Light trailer  TB O2 [1 July 2019 ]** /03, /04 
Medium trailer  TC O3 [1 July 2019 ]** nil 
Heavy trailer  TD O4 [1 July 2019 ]** nil 
* The category code may also be in the format L 1, L2, L3 etc. 
** See clause 3 .1. 
 
   DRAFT  Australian Design Rule 38/05 Trailer  Brake Systems  5 
 
   
 4. DEFINITIONS  
4.1. For vehicle categories, definitions and meanings used in this standard, 
refer to : 
4.1.1. Vehicle Standard (Australian Design Rule Definitions and Vehicle Categories) 2005 ; and 
4.1.2. Definitions in clause 1 of APPENDIX 3 of this standard.  
5. DESIGN REQUIREMENTS  FOR TRAILERS UP TO 4.5 TONNES 
‘ATM’  
5.1. Every trailer must be equipped with an efficient ‘ Service Brake System’ 
which, with the exception of trailers equi pped with an ‘Over -run Braking 
System’ , must be designed so that the braking force can be progressively 
increased and decreased by means of the ‘ Control Signal’ from the 
towing vehicle.  
5.2. In the case of trailers with a ‘ Gross Trailer Mass’ of greater than 2 tonne, 
the ‘Brake System’ must operate on all wheels.  
5.3. The ‘ Brake System’  on trailers with a ‘ Gross Trailer Mass’ up to 2 tonnes 
may be actuated for both ‘ Service Brake System’ and ‘ Secondary Brake 
System’ by the over -run of the trailer.  
5.4. Every trailer having a ‘ Gross Trailer Mass’ over 2 tonnes must be 
equipped with an efficient ‘ Emergency Brake System’ which will cause 
immediate automatic application of its ‘ Brakes’ in the event of the trailer 
accidentally becoming disconnected from the towing  vehicle.  ‘Brakes’ so 
applied must remain applied for at least 15 minutes. 
5.5. Trailers up to 4.5 tonnes ‘ATM’ are not required to comply  with  
subsequent sections of this standard.  
6. GENERAL DESIGN REQUI REMENTS FOR TRAILERS  OVER 
4.5 TONNES ‘ATM’  
6.1. A ‘Service Brake System’ must be fitted to all trailer wheels and be in 
accordance with the requirements of part 7.  
6.2. The trailer ‘ Brake System’ must be capable of being actuated from the 
towing vehicle by means of a connection between the trailer and towing vehicle with a performan ce not less than that specified for the 
‘Emergency Brake System’ in part 8 after any one failure in a ‘ Brake 
Device’ in the trailer ‘ Brake System’ . 
6.3. A ‘Parking Brake System 38/...’ must be fitted and must meet the 
requirements of part 9.  
6.4. The trailer ‘ Brake System’ must restrain the trailer automatically in the 
event of a trailer break -away with a performance not less than that 
specified for the ‘ Emergency Brake System’ in part 8. 
6.5. A ‘Brake System’ which utilises ‘ Stored Energy’ to actuate the ‘ Service 
Brake System’ must be designed so that when the ‘ Supply Line’ energy 
level is reduced at a rate of not less than 0.15E/sec (100 kPa/sec) the following conditions are met;   DRAFT  Australian Design Rule 38/05 Trailer  Brake Systems  6 
 
   
 6.5.1. the ‘Brake System’  must not start to automatically apply the ‘Brakes’  at a 
‘Supply Line’  energy level of more than 0.65 ‘E’  (420 kpa) and,  
6.5.2. the ‘Brake System’ must start to automatically apply the ‘ Brakes’ at a 
‘Supply Line’ energy level not less than:  
6.5.2.1. 0.31 ‘E’ (200 kPa) where the maximum braking effectiveness of the 
‘Brakes’ so applied is dependent on ‘Stored Fluid Energy’ or;  
6.5.2.2. 0.24 ‘E’ (155 kPa) where the maximum braking effectiveness of the  
‘Brakes’ so applied is not dependent on ‘Stored Fluid Energy’ and;  
6.5.2.3. with the  ‘Supply Line’ energy level at 0.0  ‘E’ the braking effectiveness 
must be at least that specified for the  ‘Emergency Brake System’ in 
clause 8.1.  
6.6. The ‘ Brake System’ must be designed so that no single failure in a ‘ Brake 
Device’ in the ‘ Service Brake System’ , except of a ‘ Supply Line’ or 
‘Control Line’ , must  cause the ‘ Brakes’ to apply without a ‘ Control 
Signal’ provided by the towing vehicle.  
6.7. Manual devices for the isolation of faulty devices or brake circuits may be included in the ‘ Brake System’ but automatic devices of the type that 
normally remain passive and whose function cannot readily be checked during normal operation of the trailer are not permitted. For the purposes of this clause normal operation also includes the activity of coupling and 
uncoupling the trailer connections. 
6.8. Where a trailer is fitted with an auxiliary park brake release device, enabling stored energy actuation or release of any part of the ‘ Brake 
System’ to be cut out, the device must be such that the ‘ Brake System’ is 
restored to normal no later than on the resumption of the supply of ‘Stored Energy’ to the  trailer from the towing vehicle.  
6.9. All components and devices in the ‘ Brake System’ must meet or exceed 
at least one appropriate and recognised international, national or association standard, where such standards exist, or the relevant parts thereof.  ‘Recognised’ can be taken to include SA, SAE, BS, JIS, DIN, performance and design related ISO standards and UN regulations . 
6.10. Brake line couplings must not be interchangeable and must be polarised. Couplings must comply with the requirements – AS 4 945:2000, 
‘Commercial road vehicle – Interchangeable quick release couplings for 
use with air -pressure braking systems’ where applicable or compatible 
couplings which meet the requirements of ISO 1728: 2006 ‘Road vehicles 
– Pneumatic Braking connections between motor  vehicles and towed 
vehicles – Interchangeability’ may be used.  
6.11. Each air reservoir in a compressed air ‘ Brake System’ must be fitted with 
a manual condensate drain valve at the lowest point.  An automatic condensate valve may be fitted provided it also dra ins the lowest point. 
The manual drain valve may be incorporated in the automatic valve.  
   DRAFT  Australian Design Rule 38/05 Trailer  Brake Systems  7 
 
   
 6.12. Each ‘ Brake System’ must incorporate devices which automatically 
compensate for any increased movement of its components arising from 
wear.  Such devices must themselves contain provision for securing them throughout their working range in any position to which they adjust. 
6.13. Except for braking systems capable of producing asymmetric braking in response to prevailing tractive conditions , or as required by the ‘ Braking 
Systems’  of clause 7.2, each ‘ Brake System’ must, when applied, produce 
a resultant braking force acting along the longitudinal centre line of the trailer . 
6.14. Where the ‘Supply Line’ supplies energy to devices other than ‘Brake 
Power Unit 35/...’ including spr ing brakes , the design must be such that 
all the ‘ Brake Power Unit 35/...’ are preferentially charged  until the 
supply line reaches an energy level of not less than 0.69 ‘ E’ (450 kPa ); or 
6.14.1. the spring brakes must not release before there is sufficient pressu re in 
the service air tank to allow  application of a service brake to at least the 
emergency ERC as required by clause 8.1.  
6.14.2. Systems that utilize spring brakes for emergency and parking brakes are 
deemed to comply with this requirement if the parking/emergency brakes do not release until a service tank pressure of 0.435 ‘ E’ (283 kPa) is 
reached.  
6.14.3. Spring  brake release is deemed to occur when the brake friction materials 
cease to contact.  
6.15. The first call on the ‘ Stored Energy’ must be that of the ‘ Brake System’ .  
Any other demand for ‘ Stored Energy’ must be disconnected 
automatically if the ‘ Stored Energy’ level falls below 0.69 ‘E’ (450 kPa).  
6.16. Where separate methods of actuation are provided for any of the functions of the ‘ Brake System’ , the actuat ion of one function must not 
cause the operation of another function.  
6.16.1. Where a trailer is equipped with both a pneumatic ‘Control Line’  and an 
electric ‘Control Line’ , ‘Control Signals’  for both ‘Control Lines’  must 
be present at the coupling head and the t railer must use the electric 
‘Control Signal’  unless this signal is deemed to have failed. In this case 
the trailer must  automatically switch to the pneumatic ‘Control Line’ . 
6.17. ‘Stored Energy’ devices must be safeguarded to prevent depletion of the 
‘Stored F luid Energy’ through failure of any part of the supplying 
system.  
6.18. In the case of a compressed air ‘Brake system’,  a pressure test connection 
complying with clause 4 of ISO Standard 3583- 1984 must be fitted at 
either the inlet to, or in the body of, the bra ke chamber with the slowest 
reaction time in each ‘Axle Group’ (in respect of brake timing as specified in part 16 ). 
   DRAFT  Australian Design Rule 38/05 Trailer  Brake Systems  8 
 
   
 6.19. Where a ‘Retractable Axle’ is fitted, a trailer  has a number of 
‘Configurations’. It must be demonstrated by physical testing or by 
calcu lation as described in the appropriate sections of this rule that in 
each ‘Configuration’, the trailer complies with the laden condition 
requirements of this rule for that ‘Configuration’. The laden condition for  
‘Configurations’ with the  ‘Axle’ retracted must be considered to be when 
the ‘Axle Group’ is laden to the  ‘Prescribed Transition Mass’ for the  
‘Configuration’ being considered. As the trailer must automatically change its  ‘Configuration’ at the ‘Prescribed Transition Mass’ by 
lowering an ‘Axle’ , for the purpose of demonstrating compliance with the 
requirements of this clause, the automatic system for lowering the axle may be rendered inoperative.  
6.19.1. The requirements of clause 6.19 do not apply to:  
6.19.1.1. the ‘Service Brake System’ compatibility requirements  as described in 
clause 7.1.6. This requirement must only be demonstrated in the conditions as specified in clause 10.6; or  
6.19.1.2. the service Brake Actuation Time Test as described in clause 16.1  
6.19.2. When determining the Park Brake Effectiveness either by test as in  part 
15 or by calculation as in part 20, the ‘Aggregate Trailer Mass’ is  to be 
multiplied by the ratio of the ‘Prescribed Transition Mass’ for each ‘Configuration’ divided by the ‘Group Gross Axle Load Rating’. 
6.19.3. When determining the Emergency Brake Effecti veness either by test as 
in part 14 or by calculation as in part 19, the ‘Gross Trailer Mass’ is to 
be multiplied by the ratio of the ‘Prescribed Transition Mass’ for each ‘Configuration’ divided by the ‘Group Gross Axle Load Rating’. 
7. SERVICE BRAKE SYSTEM  
7.1. General Requirements  
7.1.1. The ‘ Service Brake System’ must be designed so that the braking force 
can be progressively increased and decreased by means of the ‘ Control 
Signal’ from the towing vehicle.  
7.1.2. The combined total energy capacity of energy storage devices incorporated into the ‘ Service Brake System’ must be not less than 8 
times the combined maximum energy capacity of the service brakes actuating devices.  
7.1.2.1. In the case of compressed air ‘ Braking Systems’ , the ratio of air reservoir 
volume to actuator volume will be taken as being the ratio of energy capacity.  
7.1.2.2. The volume of an actuator  (brake chamber ) of a type specified in Table 2 
is taken as being either the rated volume listed in th is table or the actual 
volume of the actuator  at the maximum travel of the a ctuator 
piston/pushrod, whichever is lower.  
7.1.2.3. The volume of a n actuator not listed in Table 2 is the actual volume of 
the actuator  at the maximum travel of the actuator  piston/pushrod.  DRAFT  Australian Design Rule 38/05 Trailer  Brake Systems  9 
 
   
 7.1.3. The elapsed time, as measured in accordance with the procedure 
specified in part 16 for measuring brake actuation time response must not 
exceed in the case of:  
7.1.3.1. any brake actuator of any ‘ Axle Group’ on the trailer, 0.4 seconds; and  
7.1.3.2. any trailer or dolly rear service coupling for towed trailers , 0.4 seconds.  
7.1.4. In the case of trailers, other than ‘ Pig Trailers ’ that are not ‘ Converter 
Dollies ’, the elapsed time as measured in accordance with the procedure 
specified in part 16 for measuring brake release time must not exceed, in 
the case of:  
7.1.4.1. any trailer or dolly rear service cou pling for towed trailers, 0.65 seconds.  
7.1.5. At least one ‘Axle’  in each ‘Axle Group’  of each ‘Unique’  trailer ‘Service 
Brake System’  must be shown to commence to develop a braking force, 
at a ‘Control Signal’  (measured at each ‘Control Line’  coupling) not 
exceeding 0.154 ‘E’ (100 kPa for the  pneumatic ‘Control Line’  and the 
equivalent digital demand value in the case of any electric ‘Control 
Line’ ), when at ‘UTM’ with the energy storage devices charged to the 
‘Nominal Minimum Energy Level’ . 
7.1.5.1. For the purpose of this clause, an ‘Axle’  is deemed to have commenced to 
develop a braking force, when the total static brake torque for the axle concerned reaches the lesser of:  
(a) 100 N.m; or  
(b) 1 per cent of the product of the static vertical load (N) on the ‘ Axle’  
concerned and the rolling radius of the tyre s (m) fitted to the wheels, 
at ‘UTM’.  
7.1.5.2. Compliance with this clause may be shown by:  
(a) Lifting the wheels of the ‘Axles’  of each ‘Axle Group’  above the 
ground, so they can be freely rotated by hand when t he pre ssure in 
the ‘Control Line’  is 0 kPa;  
(b) Setting any ‘Variable Proportioning Brake System’  (including an 
electronic load proportioning system) to the ‘UTM’ operating condition, without increasing the torque required to rotate the wheels;  and 
(c) Gradually increas ing the ‘Control Signal’  (measured at the ‘Control 
Line’  coupling) until the total torque required to begin to rotate the 
wheel s/hubs of at least one ‘Axle’  in each ‘Axle Group’ , reaches the 
lesser of:  
i. 100 N.m; or  
ii. 1 per cent of the product of the s tatic vertical load (N) on the 
‘Axle’  concerned and the rolling radius of the tyre s (m) fitted to 
the wheels, at ‘UTM’.   DRAFT  Australian Design Rule 38/05 Trailer  Brake Systems  10 
 
   
 7.1.6. Each ‘ Unique’ trailer ‘ Service Brake System’ must  be shown by either 
testing  in accordance with part s 10 and 11, or by calculation based  on 
data for ‘ Approved’ components in accordance with clause 17, to have 
‘Established Retardation Coefficients’ between the ‘ Upper Boundary’ 
and the ‘ Lower Boundar y’ of: 
(a) Figure 1 when fully laden; and 
(b) For trailers not equipped with an ‘Antilock System’  (only where 
permitted by clause 7.2.1.1) , but fitted with a ‘Variable 
Proportioning Brake System’ , Figure 2 when at ‘UTM’, and 
progressively between Figure 2 and Figure 1 for intermediate 
states of load.  
7.1.6.1. The requirements specified in this clause are applicable for trailers equipped with a pneumatic ‘Control Line’ , as well as for trailers with an 
additional electric ‘Control Line’ . In both cases, the reference value 
(horizontal coordinate  of the figure) will be the value of the transmitted 
pressure in the ‘Control Line’ : 
(a) For a pneumatic ‘Control Line’ , this will be the actual pneumatic 
pressure in the ‘Control Line’ ; 
(b) In the case of  an additional electric ‘Control Line’ , this will be the 
pressure corresponding to the transmitted digital demand value in the electric ‘Control Line’ , according to ISO 11992:2003 including 
ISO 11992- 2:2003 and its Amd.1:2007. 
 Trailers equipped with both pneumatic and electric ‘Control Lines’  must  
satisfy the requirements of this clause  for each  ‘Control Line’ . However, 
identical braking characteristic curves are not required  for each of  these 
‘Control  Lines’ . 
7.1.6.2. ‘Established Retardation Coefficients’  may be determined by calculation 
for intermed iate states of load between ‘UTM’ and fully laden.  These 
calculations must include not less than 5 points and include any critical point. 
7.1.6.3. The ‘Upper Boundary’ of Figure 2 may be increased by up to 40 per cent in the case of  a trailer with a ‘Variable Proportioning Brake System’ , 
which can be set to achieve a retardation response between the conventional ‘Upper Boundary’ and the ‘Lower Boundary’ of Figure 2, but is adjusted to allow for the braking responses of particular towing vehicles not equipped with a  ‘Variable Proportioning Brake System’ . 
7.1.7. Each ‘ Unique’ trailer ‘ Service Brake System’ must be shown by either 
testing in accordance with parts 10 and 13 or by the calculation based on 
data for ‘ Approved’ components in accordance with part 18, to meet the 
requirements of clause 13 .1. 
7.1.8. Trailers fitted with a ‘Variable Proportioning Brake System’ , including 
an electronically controlled brake force distribution system ( including for 
example as part of a ‘Vehicle Stability Function’ ), must meet the  
requirements of APPENDIX 1.   DRAFT  Australian Design Rule 38/05 Trailer  Brake Systems  11 
 
   
 7.2. Electric ‘Control Line’ , ‘Antilock System’ and ‘Vehicle Stability 
Function’ r equirements  
7.2.1. Except as set out in clause 7.2.1.1 below , trailers  must  be equipped on 
each ‘Axle Group’  with  an ‘Antilock System’  which meets the 
requirements of APPENDIX 2.  
7.2.1.1. A ‘Converter Dolly’  and any trailer fitted with an ‘Axle Group’  
arrangement consisting of more than four tyres in a row of ‘Axles’  or 
more than four ‘Axles’  in an ‘Axle Group’ , need not be equipped with an 
‘Anti lock System’ . 
7.2.1.1.1. Where a trailer is not equipped with an ‘Antilock System’  (only if  
permitted by clause 7.2.1.1 above ) or a ‘Variable Proportioning Brake 
System’ , the information on the Vehicle Plate referred to in clause 8 of 
ADR 61/... must include the words ― “THIS VEHICLE  IS NOT 
FITTED WITH ANTILOCK BRAKES  OR VARIABLE 
PROPORTIONING BRAKES ”. 
7.2.1.1.2. Where a trailer is not equipped with an ‘Antilock System’  (only if  
permitted by clause 7.2.1.1 above ) but is fitted with a ‘Variable 
Proportioning Brake System’ , the information on the Vehicle Plate 
referred to in clause 8 of ADR 61/... must include the words ― “THIS 
VEHICLE  IS NOT FITTED WITH ANTILOCK BRAKES”.  
7.2.1.2. Notwithstanding clause 7.2.1.1 above, the requirements of APPENDIX 2 must als o be met if  an ‘Antilock System’  is fitted to a ‘ Converter Dolly’  
or any trailer fitted with an ‘Axle Group’  arrangement consisting of more 
than four tyres in a row of ‘Axles’  or more than four ‘Axles’  in an ‘Axle 
Group’ . 
7.2.2. Except as set out in clause 7.2.2.1 below , category TD trailers must be 
equipped with a ‘Vehicle Stability Function’  which include s at least 
‘Roll-over Control ’ and meet s the requirements of APPENDIX 3.  
7.2.2.1. A ‘Converter Dolly’  and any trailer  fitted with an ‘Axle Group’  
arrangement consisting of more than four tyres in a row of ‘Axles’  or 
more than four ‘Axles’  in an ‘Axle Group’ , need not be equipped with a 
‘Vehicle Stability Function’. If a ‘Vehicle Stability Function’ is fitted  to 
such a trailer , this function may be manually disabled , provided this does 
not adversely affect the performance of any ‘Antilock System’ , the power 
supply to any towed trailer (s) and/or the transmission  of any electric 
‘Control Signal’ . 
7.2.3. Trailers equipped with an electric ‘Control Line’ , an ‘A ntilock System’ , 
or a ‘Vehicle Stability Function’ , must meet the requirements of 
APPENDIX 4.  
7.2.4. Notwithstanding the fitment pre conditions  of clause 7.2.3 above  (i.e. 
fitment of  an electric ‘Control Line’ , an ‘Antilock System’,  or a ‘Vehicle 
Stability Function’) , any trailer (including a ‘Converter Dolly’) equipped 
to tow another trailer with an ‘ATM’ greater than 4.5 tonnes, must meet 
the requirements of part  3 (clauses 3.1 and 3.2) of APPENDIX 4.   DRAFT  Australian Design Rule 38/05 Trailer  Brake Systems  12 
 
   
 8. EMERGENCY BRAKE SYST EM 
8.1. Each ‘ Unique’ trailer ‘ Emergency Brake System’ must be shown by 
either test in accordance with part 10 and clause 14 .1 or by the 
calculation based on data for ‘ Approved’ components in part 19, to have 
an ‘Established Retardation Co- efficient’ of not less than 0.18 and to be 
able to sustain a ‘ Brake’ force required to obtain an ‘ ERC’ of 0.18 for a 
period not less than 15 minutes. 
8.2. The ‘ Emergency Brake System’ may utilise parts of the ‘ Service Brake 
System’ on the condition that any one failure of a ‘ Brake Device’ in the 
‘Service Brake System’ does not prevent the ‘ Emergency Brake System’ 
from achieving its performance requirement. For the purpose of this  
clause, the ‘ Brakes ’ and any mechanical linkage connected directly 
thereto, must be considered as not subject to failure.  
8.3. In the case of  ‘Semi-Trailers’, when disconnected  from the ‘Pri me-
Mover’, the failure of  any structure designed to support the front of the 
trailer must not reduce the effectiveness of the ‘ Emergency Brake 
System’ to less than half that required by clause 8.1. 
8.4. ‘Emergency Brake Systems’ that employ ‘ Stored Fluid Energy’ to hold 
them in the release position must be provided with an auxiliary release 
mechan ism. The auxiliary device, control or tool, may rely on fluid 
energy stored within the trailer brake system, and must be attached to the trailer chassis rail, or equivalent structure, forward of the forward most ‘Axle’ on the rear ‘ Axle Group’ on the right hand side of the trailer.  
8.4.1. If the auxiliary device utilises stored energy then, with the energy  storage 
devices initially charged to 1.0 ‘ E’ the release system must have 
sufficient reserve to provide at least 3 applications and releases of the ‘Emergency Brake System ’ when the towing vehicle is disconnected.  
9. PARKING BRAKE SYSTEM   
9.1. The ‘ Parking Brake System 38/...’ must be independent of the ‘ Service 
Brake System’ except that the brakes and any mechanical system attached directly thereto may be common.  
9.2. The ‘ Parking Brake System 38/...’ must be able to be applied by means of 
a single ‘ Cont rol’ and once applied, must be able to be held in position 
by purely mechanical means.  
9.3. It must not be possible to release the Parking Brake unless a means of 
immediately reapplying it is available.  
9.4. The parking brake must operate when the ‘Supply Line’  ener gy level 
drops below 0.24 ‘E’ (155 kP a). The provisions of clause 9.3 do not 
apply to the auxiliary release mechanism required by clause 8.4 but the other provisions of clause 8.4 must apply.  
9.5. Additional parking brake facilities are permitted provided that the requirements of clauses 9 .2, 9.3 and 9.4 are met.   DRAFT  Australian Design Rule 38/05 Trailer  Brake Systems  13 
 
   
 9.6. Each ‘ Unique’ trailer ‘ Parking Brake System 38/...’ must be shown to be 
capable of holding the trailer stationary on an 18 percent gradient in 
either direction by either:  
9.6.1. test in accordance with part 10 and clause 15.1; or  
9.6.2. test in accordance with part 10 and clause 15.2; or  
9.6.3. calculation based on data for ‘ Approved’ components in part 20. 
10. GENERAL PERFORMANCE ROAD TEST CONDITIONS   
10.1. The ambient temperature at the test site must be greater than 0°C and less than 40°C. 
10.2. All road tests must be conducted with tyres fitted of the size specified by the ‘Manufacturer’ as original equipment and must be inflated to 
pressures not less than those recommended by the ‘ Manufacturer’ . 
10.3. Braking tests must be carried out on appr oximately level surfaces.  
10.3.1. Where the levels are unsurveyed, the test must be completed in both 
directions, the brakes being applied over the same section, and the two results averaged to determine the final result.  
10.3.2. Where the difference in start and finish elevations for a brake test, 
expressed as a percentage of the ‘Stopping Distance’, is known, the brake test need only be completed in one direction and the result corrected for any difference in elevation exceeding 1 percent.  
10.4. The wind speed difference betwe en two tests in opposite directions, or 
against the direction of travel in the case of a single brake test, must not exceed 15 km/h. 
10.5. The towing vehicle used to facilitate the tests must be of a type normally employed to tow the particular trailer under test and must have enough power to attain the initial speed required for the specified braking tests.  
10.6. All road tests must be conducted with energy storage devices charged to ‘Nominal Minimum Energy Level’  and the  ‘Axle Groups’ loaded , unless 
otherwise requ ired by this rule , to: 
10.6.1. The ‘GTM’ and in a separate series of test s to the values allowed by 
Table 1 if this results in a trailer mass lower than ‘GTM’;  and 
10.6.2. In the case of trailers fitted with a ‘Variable Proportioning Brake System’  
in a separate test to the ‘UTM’; and  
10.6.3. In the case of trailers not equipped with an ‘Antilock System’ , solely in 
accordance with clause 7.2.1.1 above, but fitted with a ‘Variable Proportioning Brake System’ , in a separate series of tests to the ‘UTM’.  
10.7. The t est surface must be either concrete or bitumen pavement and must 
be free from loose material.  
10.8. No towing vehicle braking system or other contrived means must contribute to braking effort and the towing vehicle engine must be declutched or neutral engaged, during the braking tests required by this rule.  DRAFT  Australian Design Rule 38/05 Trailer  Brake Systems  14 
 
   
 10.9. The ‘ Brakes’ may be burnished before conducting any effectiveness tests 
according to the brake manufacturer’s recommended procedures.  
10.10. The ‘ Brake System’ must be adjusted in accordance with the brake 
manufactur er’s recommendations before performance tests are 
conducted.  
10.11. The performance requirements must be met with no deviation of the 
vehicle from its course greater than 300 millimetres.  
10.12. No part of the ‘ Brake System’ shall  exceed 100°C immediately prior to 
the commencement of a brake test sequence.  
11. SERVICE BRAKE EFFECT IVENESS TEST CONDITI ONS  
11.1. Except as provided in clause 11.1.1 below, t he initial speed at the point 
where trailer braking commences must be, 58 to 64 km/h. 
11.1.1. For special trailers having a design speed l ess than 58 km/h, t he initial 
speed at the point where trailer braking commences must not be less than the ‘Manufacturer’s’ nominated design speed.  
11.2. The trailer must be braked to a stop from initial speed starting with a ‘Control Signal’ of 0.2 ‘ E’ and in increasing increments of not greater 
than 0.2 ‘ E’ for subsequent stops until an ‘Established Retardation 
Coefficient’  of not less than 0.45 is achieved.  
11.3. In the case of a compressed air ‘ Brake System’ the ‘ Control Signal’, 
applied  to the ‘Control Line’ at t he front of the trailer, must reach 65 
percent of the final value in less than 0.4 second.  
11.4.  ‘Stopping Distance’ or ‘Stopping Time’ may be used to calculate the ‘ERC’ according to the equations in clause 11.5.  
11.5. The ‘ Service Brake System’ ‘ERC’ must be determ ined according to the 
following as required:  
 
 
 where:  
 V  is the initial speed in km/h  
 S  is the  ‘Stopping Distance’ in metres  
 T   is the ‘Stopping Time’ in seconds  
 T
R  is the response time measured from the time the ‘Control’ leaves the 
‘Initial Brake Control Location’ until the energy level at the least favoured actuator reaches 65 percent of final value  
 ‘Total Combination Mass’  in tonnes  
 ‘Total Trailer Axle Load’  in tonnes with the trailer loaded as specified in 
clause 10.6   
 
 DRAFT  Australian Design Rule 38/05 Trailer  Brake Systems  15 
 
   
 11.6. The comput ed ‘Established Retardation Coefficients’  determined from 
clause 11.5 must comply with clause 7.1.6.  Where a test was not 
conducted at 1.0 ‘E’  the ‘ERC’  from a test conducted at 0.8 ‘E’ or greater 
may be increased pro -rata to derive the ‘ERC’  at 1.0 ‘E’.  
11.7. No trailer wheels must remain locked, except below 15 km/h, during completion of the braking tests required by part 11. 
11.8. Allowance must be made for the effect of the increased rolling resistance resulting from the combination of vehicles being used to carry  out the 
tests.  
11.9. Computer simulation of the requirements of this part  11 is allowed where 
the simulation is sufficiently sophisticated and has been  ‘Approved’ on 
the basis of an adequate back to back comparison with physical test results.  
12. DOG TRAILER FRICTI ON UTILISATION 
12.1. In the case of ‘Dog Trailers’ and with any ‘ Antilock System’  disengaged 
or otherwise made not operational, at least one front ‘Axle’ must skid before at least one rear ‘Axle’ at an ‘ERC’ greater than:  
 (a) 0.3 in the case of two ‘Axle’ ‘Dog Trailers’;  
 (b) 0.15 in the case of ‘Dog Trailers’ with three or more ‘Axles’.  
12.2. The test must be conducted in accordance with part 11 with the ‘Control Signal’ and surface type selected to demonstrate the requirement of clause 12.1 above.  
12.3. The initial speed requirement of part 11 does not apply.  
13. SERVICE BRAKE FADE E FFECTIVENESS TEST  
13.1. The ‘Service Brake System’ must, on the next application after not less than 20 successive applications, each not more than 70 seconds after the preceding one and with the total of 20 applications completed within 20 minutes, of the trailer ‘Brakes’ from an initial speed of V
1 km/h to a final 
speed as calculated below or by clause 13.2, achieve a calculated ‘Established Retardation Coefficient’, when tested in accordance with part 11, at a nominated ‘Control Signal’ level, of not less than 60 percent 
of the value obtained at that ‘Control Signal’ level for the Service Brake Effectiveness Test required by part 11 nor less than 80 percent of the value specified by the lower boundary of Figure 1 at that ‘Control Signal’ level. The nominated ‘Control Signal’ level chosen must not be less than that necessary to produce a calculated ‘Established Retardation Coefficient’ of 0.45 under the Service Brake test conditions described in part 11 without prior fade conditioning stops.   DRAFT  Australian Design Rule 38/05 Trailer  Brake Systems  16 
 
   
 13.2. The final speed to which the trailer has to be successively braked as part 
of the brake fade conditioning procedure must be determined from the equation:  
 
 where:  
 V
1   is the initial speed in km/h;  
 V2   is the final speed in  km/h;  
 Masses and Loads in tonnes  
13.3. The temperature (100°C) requirement of clause 10 .12 does not apply to 
the test required by clause 13.1. 
14. EMERGENCY BRAKE SYST EM EFFECTIVENESS TES T 
14.1. The ‘ Established Retardation Coefficient’, as  deter mined by clause 11.5 
must be determined by a test to the requirements of part 11 except where clause 14.2 applies, and except that:  
14.1.1. The ‘ Control Signal’ source must be left in the “off” position with no 
‘Control Signal’ being provided to the trailer control line; and  
14.1.2. The energy level in the ‘ Supply Line’ must be reduced to zero (in a 2- line 
compressed air system this will be the emergency line).  
14.2. Where the actuation of the ‘ Emergency Brake System’ depends on one or 
more sources of ‘ Stored Energy’ that are co mmon to the ‘ Service Brake 
System’ , for the purposes of testing for compliance with the requirements 
of clause 14.1, the trailer energy storage devices must be charged to an energy level no greater than 0.05 ‘ E’ above the supply level determined 
for clause 6.5, or the energy storage device level if higher, at which the ‘Emergency Brake System’ commences to activate the ‘ Brakes’ . 
14.3. Wheel -locking at ‘Established R etardation C oefficients’  above 0.18 is 
permitted.  
15. PARKING BRAKE EFFECT IVENESS TEST  
15.1. The ‘ Parking Brake System 38/...’ must be able to meet the requirements 
of clause 9.6 for a 5 minute period in each direction with the force required to actuate the parking brake not exceeding 685 N in the case of a foot operated brake and not exceeding 590 N i n the case of a hand 
operated brake.  
15.1.1. The necessary longitudinal force will be considered to have been applied 
if the sum of the force applied to the trailer towing point and the force due to the effect of gravity on the laden trailer mass, in the direction parallel to the test surface and trailer longitudinal axis, is greater than 0.18 times the ‘ Aggregate Trailer Mass’ . 
15.1.2. Where the test involves a force depending on the slope of the test surface, 
the slope must not be less than 10 percent.  
 DRAFT  Australian Design Rule 38/05 Trailer  Brake Systems  17 
 
   
 15.1.3. When the test involves the action of slope on the trailer or combination 
mass, and the towing vehicle remains connected, 1.5 percent of the 
towing vehicle mass must be subtracted from the other forces parallel to the test plane, to allow for rolling friction.  
15.1.4. The test slope  must be specified in terms of unit vertical per unit 
horizontal distance expressed as a percentage.  
15.2. The ‘ Parking Brake System 38/...’ must meet the requirements of clause 
14.1 when the ‘ Foundation Brakes’ geometry is such that a reversal of 
the required b raking torque will not reduce the ability of the ‘ Parking 
Brake System 38/...’ to generate the required braking torque.  
16. TIME RESPONSE MEASUR EMENT  
16.1. Except where hydraulic brakes are used, each ‘ Unique’ trailer ‘ Brake 
System’ must be shown to meet the requir ements of clause 7.1.3 and 
7.1.4 by testing in accordance with clause 16.3, or in accordance with part 21. 
16.1.1. Where a trailer is fitted with a ‘ Variable Proportioning Brake System’ the 
test must be conducted with the ‘ Variable Proportioning Brake System’ 
set for the fully laden case. 
16.2. A variant of a ‘ Unique’ trailer ‘ Brake System’ will be considered to be 
identical in regard to time response, when the only variation from the 
‘Unique’ ‘ Brake System’ is one or more of the following:  
16.2.1. Plumbing or energy transmissio n line lengths and number of fittings are 
reduced but other characteristics including diameter, material, type of connecting fittings and the characteristic transmission loss per unit length are not changed.  
16.2.2. Entire subsections of the ‘ Brake System’ have be en removed, as would be 
the case in converting a modular three ‘ Axle’ system to a modular two 
‘Axle’ system, such that the effect if any is to slightly increase the energy 
flow rate to and from the remaining brake sub- systems.  
16.2.3. The energy required to actuat e the substitute brake actuators to their 
maximum design level is less.  
16.3. Where a trailer ‘ Brake System’ is required to be tested for compliance 
with clauses 7.1.3 and where applicable 7.1.4 in the case of compressed air ‘Brake System’ : 
16.3.1. for a pneumatic ‘Control Line’ , the test rig described in Figure 3 must be 
calibrated in accordance with clause 16.4 and connected as described in Figure 4;  
16.3.2. for an electric ‘Control Line’ , Figure 5 gives an example of the correct 
configuration of the simulator for setting  and use and must  be used 
according to clause 1 6.10 to comply with clause 7. 1.3. 
16.3.3. Where the trailer has both a pneumatic and an electric ‘Control Line’ , the 
response time measurement for each control line must be determined independently according to the re levant procedure.   DRAFT  Australian Design Rule 38/05 Trailer  Brake Systems  18 
 
   
 16.4. The test rig described in Figure 3 must be calibrated by adjustment of the 
orifice (O) such that : 
16.4.1. upon application of the brake control valve (V) with the storage reservoir (R1) charged to 1.0 ‘ E’ (650 kPa), the time interval is between 0.18 and 
0.22 seconds from when the initial pressure drops measured between the storage reservoir and the control valve (V), or the initial pressure rises at the output of brake control valve (V) , to when the pressure at the end of 
the calibrating vessel (R2) increases to 0.65 ‘ E’ (420 kPa) ; 
16.4.2. after the pressure in the calibrating vessel (R2) has stabilised, upon release of the brake control valve (V) must be such that the time between the initial pressure drop in the calibrating vessel (R2) and the pressure  in 
the calibrating vessel (R2) reaching 0.05 ‘E’ (35.0 kPa) is between 0.4 and 0.5 seconds.  
16.4.3. Where one setting of the orifice (O) does not meet both of these conditions simultaneously, two different settings meeting the appropriate  
condition can be used in the tests prescribed in clauses 1 6.7 and 16.8.  
16.5. Where a rear service coupling for towed trailers is provided, time responses must be measured with an 800- millilitre vessel attached to the 
rear service coupling as in Figure 4.  
16.6. The test rig and the trailer e nergy storage devices must be charged to 1.0 
‘E’ (650 kPa) prior to the test being conducted and no additional energy 
must be added to the storage vessel (R1) or the trailer ‘ Supply Line’ 
during the period of the test. 
16.7. The brake actuation time must be taken from when the pressure level, measured between the storage reservoir and the control valve (V) initially drops, or measured at the output of brake control valve (V) initially rises to when the pressure in the least favoured brake actuator reaches 0.65 ‘ E’ 
(420 kPa).  
16.8. With an initial service brake application level of 1.0 ‘ E’ (650 kPa) the 
brake release time must be taken from when the pressure level, measured between the control valve and the orifice, initially drops to the greater of when the pressure in the least favoured brake actuator reaches 0.05 ‘E’ 
(35 kPa) or when the friction materials cease to contact each other.  
16.9. The brake control valve must be of a configuration such that;  
16.9.1. it permits energy to flow from the storage reservoir to the orifice (O) 
when in the “ON” position and from the orifice to waste when in the 
“OFF” position; and,  
16.9.2. it must not allow additional energy to flow into the test rig ‘ Control Line’ 
by way of its own ‘ Control Signal’;  and 
16.9.3. it must be designed so that the manner of its operat ion has no effect on 
the output response of the test rig; and  
16.9.4. it may be arranged to provide a modulated test rig output signal for other brake development purposes which will be rendered inoperative for the purpose of measuring trailer ‘ Brake System’ respo nse in accordance with 
clause 16.3.   DRAFT  Australian Design Rule 38/05 Trailer  Brake Systems  19 
 
   
 16.10. The simulator must  produce a digital demand signal in the electric 
control line according to ISO  11992- 2:2003 and its Amd.1:2007 and 
must  provide the appropriate information to the trailer via pins 6 and 7 of 
the ISO 7638:2003 connector.  For the purpose of response time 
measurement , the simulator may at the manufacturer's request transmit to 
the trailer information that no pneumatic control line is present and that 
the electric control line demand signal is generat ed from two independent 
circuits (see paragraphs  6.4.2.2.24 and 6.4.2.2.25 of ISO  11992 -2:2003 
and its Amd.1:2007).  
16.10.1. For the purpose of response time measurement  the signal produced by the 
electric simulator must  be equivalent to a linear pneumatic pressure  
increase from 0.0 to 650 kPa in 0.2 ± 0.01 second. 
17. SERVICE BRAKE EFFECT IVENESS CALCULATION  
17.1. In the case of an ‘ Axle Group’ fitted with a ‘Brake Reactive Suspension’ 
the distribution of braking effort  amongst the ‘ Axles’ in an ‘ Axle Group’ 
must be in the r ange of ‘Skid Limit’ values determined for the suspension 
in accordance with clause 22.4. 
17.2. In the case of ‘ Dog Trailers’ at least one front ‘ Axle’ must have a higher 
friction utilisation than that of at least one rear ‘ Axle’ at decelerations 
greater than:  
 (a) 0.3 g in the case of 2 ‘ Axle’ ‘ Dog Trailers’,  
 (b) 0.15 g in the case of ‘ Dog Trailers’ with 3 or more ‘ Axles’.  
17.2.1. In the case of two -‘Axle’ ‘Dog Trailers’ -the friction utilisation factors 
may be calculated according to : 
 
 
 so:  
 
 and: 
 
   
 
 
 DRAFT  Australian Design Rule 38/05 Trailer  Brake Systems  20 
 
   
  T1  Tangential Force at front wheel (N)  
 T2  Tangential Force at rear wheel (N)  
 F1   Friction utilisation factor for front wheel  
 F2   Friction utilisation factor for rear wheel  
 P 1  front ‘Axle’ static load (N)  
 P 2  rear ‘ Axle’ static load (N)  
 P total static ‘ Axle Load’ (N)  
 h height of trailer and load centre of mass (m)  
 L ‘Wheel Base’ (m)  
 z deceleration, as a proportion of acceleration due to gravity.  
17.2.2. No friction utilisation factor (F) must exceed 0.7 at z = 0.45 (a friction 
utilisation factor  of greater than 0.7 is taken as to mean that wheel lock 
would have occurred in the physical test otherwise required by part 11.  
17.3. The ‘Established Retardation Coefficient’ of the trailer must be 
calculated using the formula in clause 17.3.2 at levels of input ‘ Control 
Signal’ starting no higher than 0.2 ‘ E’ and increasing in increments of 
not more than 0.2 ‘ E’ until an ‘Established Retardation Coefficient’  of 
not less than 0.45 is achieved.  
17.3.1. All calculated ‘Established Retardation Coefficient’ values must lie 
between the upper and lower boundaries of Figure 1 or Figure 2 , as 
specified in clause 7.1.6.  
17.3.2. The ‘Established Retardation Coefficient’ must be calculated by : 
 
 where:  
 e  is the value of  ‘E’  
 C is the ratio of output Signal Level to ‘Control Signal’ strength for 
the ‘Control System’ for the ‘Axle’ concerned  
 T is the ‘ Brakes’ output torque per unit input signal to the ‘ Brakes’ 
actuator from output of the ‘ Control System’ for the ‘Axle’ 
concerned  
 R is the rolling radius of the tyre on the wheel  
 P is the static load on the ‘ Axle’ concerned  
 1, 2, etc.  are subscripts referring to the concerned ‘ Axle’  
 ‘Total Trailer Axle Load’  in tonnes with the trailer loaded as specified in 
clause 10.6   
 DRAFT  Australian Design Rule 38/05 Trailer  Brake Systems  21 
 
   
 18. SERVICE BRAKE FADE CALCULATION 
18.1. The ‘ Service Brake System’ will be considered to have sufficient brake 
fade resistance to meet the r equirements of this rule if the  ‘Gross Axle 
Load Rating’ of each ‘Foundation Brake’ rated according to the fade test 
in clause 22.3.6 is gr eater than the ‘Gross Trailer Mass’ multiplied by the 
percentage of total brake torque provided by that  ‘Foundation Brake’ for at least one ‘Control Signal’ level necessary to produce a calculated  
‘Established Retardation Coefficient’ of not less than 0.45 under the Service Brake test Conditions described in part 11  without prior fade 
conditioning stops. 
19. EMERGENCY BRAKE SYST EM CALCULATION.  
19.1. The ‘Established Retardation Coefficient’  for the ‘Emergency Brake 
System’  must be determined by computing the total braking force (kN) at 
the wheels to which emergency brakes are fitted and dividing by 
[9.81 ×  ‘Gross Trailer Mass’ (tonnes)]. 
19.2. The braking force at each ‘ Axle’ must be calculated according to : 
 
 where:  
 F is the tangential force at the braked wheels on the  ‘Axle’ concerned  
 A is the input to the emergency brakes actuator in units of ‘ E’   
 T is the ‘ Brakes’ output torque per 1.0 ‘ E’ for the ‘Emergency Brake 
System’   
 R is the rolling radius of the tyre fitted to the wheel  
19.2.1. Where the actuating force is depen dent on the stroke, as in the case of 
spring brakes, the value of A used in the equation above must be that 
corresponding to the ‘ Brakes’ actuator stroke achieved by the  
‘Emergency Brake System’ . This can be determined by plotting on a 
graph of  ‘Control Si gnal’ versus stroke as detailed in clauses 19.2.2 and 
19.2.3:  
19.2.2. The input to the emergency brakes actuator in units of ‘ E’ from the data 
provided for the  ‘Control System’ at various strokes; and 
19.2.3. The ‘Foundation Brake’ stroke achieved at various  ‘Control Syst em’ 
inputs. 
20. PARKING BRAKE CALCUL ATION  
20.1. The gradient, expressed as a percentage, on which the ‘Parking Brake System 38/...’ can hold the trailer must be determined by computing the total braking force at the wheels (N) to which the  ‘Parking Brake System 
38/...’ is fitted and dividing by [98.1 x ‘Aggregate Trailer Mass’ 
(tonnes)] . RT A   F×= DRAFT  Australian Design Rule 38/05 Trailer  Brake Systems  22 
 
   
 20.2. The braking force at each ‘ Axle’ must be calculated according to : 
 
 where:  
 F is the tangential force at the braked wheels on the ‘ Axle’ concerned  
 A is the input to the park brake  actuator in units of ‘ E’  
 T is the ‘ Brakes’ output torque per 1.0 ‘ E’ for the ‘Park Brake System’   
 R is the rolling radius of the tyre fitted to the wheel.  
20.3. The provisions of clause 19.2.1, 19.2.2 & 19.2.3 must apply.  
20.4. When ‘ Emergency Brake System’ perfo rmance data is used to 
demonstrate compliance of the ‘ Parking Brake System 38/...’ , the 
geometry of the ‘ Brakes’ must be such that brake effectiveness will be 
not less in the reverse direction. 
21. TIME RESPONSE  
21.1. The time response of a ‘ Service Brake System’ m ay be taken as 
complying with the requirements of this rule if the ‘ Service Brake 
System’ is installed in a manner identical to that prescribed in the 
documentation describing the ‘ Approved’ ‘ Control System’ used, except 
as allowed in clause 21.2 . 
21.2. Actuator  volumes at full  ‘Foundation Brake’ stroke and line lengths may 
be reduced and actuator volumes at the point when the ‘Foundation Brake’ friction materials cease to contact each other may be increased (for release response test) from those specified in the  ‘Approved’ 
‘Control System’ documentation, but other devices, fittings and 
dimensions may not be changed.  
22. SPECIFICATION OF BRAKE SYSTEM COMPONENTS   
22.1. Sub- assemblies of ‘ Brake System’ components may be ‘ Approved’ by the 
‘Administrator’ as part of the ‘ Brake System’ approval process where 
information has been supplied in accordance with the requirements of the appropriate sub -paragraphs of part  22. 
22.2. ‘Control System’  
22.2.1. The ‘Control System’ must be characterised by determining the ‘Control 
System’ ratio at no t less than five points in the range of  ‘Control Signal’ 
inputs at 0.2 ‘E’ to 1.0 ‘E’. These points must be equally spaced except where the relationship within that range is non- linear, in which case the 
points must include each critical point . 
22.2.1.1. The ‘Control System’ ratio for each axle is the Output Signal level as a percentage of ‘Control Signal’  level.  
22.2.1.2. The input must be taken at the trailer coupling.  
22.2.1.3. The output must be taken at the outlet end of the line to the service brake actuator.  RT A   F×= DRAFT  Australian Design Rule 38/05 Trailer  Brake Systems  23 
 
   
 22.2.2. The input signal strength must be the final value of the applied signal and 
must be applied to the ‘ Control System’ such that it rises from zero to 65 
percent of the final value in not more than 0.22 second. In the case of air ‘Brake System’s’ the input ‘ Control Signal’ st rength (kPa) will be 
measured at the trailer ‘ Control Line’ coupling.  
22.2.3. The output signal strength must be the final value of the signal generated for control of the ‘ Brakes’ actuator and which must be reached in not 
more than two seconds. The output signal strength will be measured in the actuator attached to each output having a fundamentally different relation to the input. In the case of air ‘ Brake Systems’ a  ‘Control Signal’ 
path having additional pressure limiters, relay valves or other active devices w ill be considered as being fundamentally different.  
22.2.4. Time response must be measured where necessary in accordance with part 16. 
22.2.5. Where the ‘ Control System’ is not installed on an actual trailer, it must be 
installed in an essentially identical manner, in the  laboratory, with all 
bends, fittings and worst case line lengths and representative actuator volumes installed.  
22.2.6. For the application test, clause 16.7, the actuator displacement must be the largest volume for which the ‘ Control System’ is designed and it m ay 
be represented by an equivalent fixed volume. 
22.2.7. The release test, clause 1 6.8, must commence at an actuator displacement 
corresponding to the largest volume for which the ‘Control System’ is 
designed. Alternatively , the actuators may be replaced by an equ ivalent 
fixed volume . 
22.2.8. All relevant test conditions pertaining to part 10 must be complied with.  
22.2.9. The relationship between brake actuator volume and stroke must be measured and plotted from zero to full actuator stroke. 
22.2.9.1. If the relationship between stroke and volume is not linear, all critical 
points must be measured and plotted. 
22.2.9.2. The value of the maximum brake actuator design stroke and volume must be stated.  
22.3. ‘Foundation Brakes’  
22.3.1. The effectiveness of the ‘ Foundation Brakes’ must be characterised by 
comparing th e energy level of the signal provided to the ‘ Brakes’ 
actuator against the output brake torque of the ‘ Brakes’ device at not less 
than five points in the range 0.2 ‘ E’ to 1.0 ‘ E’. These points must be 
equally spaced .  Where a test was not conducted at 1.0 ‘E’, the torque 
from a test conducted at 0.8 ‘E’ or greater may be increased pro -rata to 
derive output torque at 1.0 ‘E’.  
22.3.2. Parameters relevant to the specification of the ‘Brakes’ actuator including its stroke at each energy level of the signal provided to the ‘ Brakes’ 
actuator must be recorded. In the case of ‘ S-Cam’ air systems this will 
include the actuator size, slack adjuster length and any other special feature.   DRAFT  Australian Design Rule 38/05 Trailer  Brake Systems  24 
 
   
 22.3.3. Measurements must be taken in accordance with the relevant conditions 
for the road test described in parts 10 and 11.  
22.3.4. The ‘ Brakes’ must be burnished before conducting any effectiveness tests 
according to the brake manufacturer’s recommended procedures.  
22.3.5. Specification of effectiveness for ‘Foundation Brakes’ must be on the 
basis of ‘ Axle’ performance with two brake assemblies rather than wheel 
performance.  
22.3.6. The ‘Foundation Brake’ must, on the next application after not less than 
20 successive applications, each not more than 70 seconds after the preceding one and with the total of 20 applications completed within 20 minutes, of the trailer  ‘Brakes’ from an initial speed of V
1 km/h to a final 
speed as calculated by clause 22.3.6.1, achieve a calculated brake tor que, 
when tested in accordance with part 11, at a nominated energy level of the signal provided to the ‘ Brakes’ actuator, of not less than 60 percent of 
the brake torque achieved at that Actuator Supply Energy level when 
tested in accordance with clause 22.3.1. The chosen, nominated energy 
level of the signal provided to the ‘ Brakes’ actuator, must not be less than 
that necessary to produce a calculated ‘Established Retardation 
Coefficient’ of 0.45 under  the Service Brake T est Conditions described in 
part 11 when laden to the  ‘GALR’ without prior fade conditioning stops.  
22.3.6.1. The final speed to which the trailer has to be successively braked as part of the brake fade conditioning procedure must be determined from the 
equation:  
 
 where:  
 V
1 is the initial speed in km/h 
 V2  is the final speed in km/h  
 Masses and Loads in tonnes  
22.3.6.2. The temperature (100 °C) requirement of clause 10 .3 does not apply to 
the test required by clause 13.1. 
22.4. Suspension Behaviour, ‘Brake Reactive Suspensions’  only.  
22.4.1. ‘Suspension Systems’  for other than hinged drawbar ‘ Pig Trailers ’. 
22.4.1.1. The suspension must be installed according to the ‘Manufacturer’s’ 
instructions to a representative trailer, be fitted with ‘ Axles’ , wheels and 
tyres of a size appropriate to the mass rating of the suspension,  and be 
fitted with identical “Pre -calibrated” ‘ Brakes’ at each ‘ Axle’ . 
22.4.1.1.1. “Pre- calibrated” in this case means that the relationship between the 
input actuation energy level and the output torque for the ‘ Brakes’ on 
each ‘ Axle’ has been measured.   
 DRAFT  Australian Design Rule 38/05 Trailer  Brake Systems  25 
 
   
 22.4.1.2. To determine  the ‘Service Brake System’ ‘Skid Limit’ a Service Brake 
Effectiveness Test must be conducted applying the brakes on all  ‘Axles’ 
of the trailer and using the General Test Conditions of part 10 and 
generally in accordance with the particular conditions of p art 11 with  not 
less than 50% of the  ‘Suspension Systems’ rated ‘Axle Group’ load used 
in place of  ‘Gross Trailer Mass’.  Clause 11.2 need not be complied 
with.  
22.4.1.3. The test result must be reported as the value of the computed retardation force for each ‘ Axle’  divided by the greatest of the ‘ Axle’ retardation 
forces at which an ‘Established Retardation Coefficient’ of 0.45 can be 
achieved without wheel lock. 
22.4.1.3.1. In the case of ‘ S-Cam’ air ‘ Brake Systems’ the overall effect of changing 
actuator and slack adjuster si zes can be simulated by individually 
adjusting the air pressure to each ‘ Axle’.  
22.4.2. ‘Suspension Systems’  for hinged drawbar ‘ Pig Trailers’ . 
22.4.2.1. The suspension must be installed according to the manufacturer’s instructions to a representative trailer, be fitted with ‘ Axles’ , wheels and 
tyres of a size appropriate to the mass rating of the suspension, and be fitted with identical “Pre -calibrated” ‘ Brakes’ at each ‘ Axle’ . 
22.4.2.1.1. “Pre- calibrated” in this case means that the relationship between the 
input actuation energy leve l and the output torque for the ‘ Brakes’ on 
each ‘ Axle’ has been measured.  
22.4.2.2. The trailer must be laden such that the  ‘Axle Group’ load equals the 
suspension system’s rated ‘ Axle Group’ load and that the centre of 
gravity of the trailer is at the same height as for a typical trailer laden to the rated ‘ Axle Group’.  
22.4.2.3. To determine the  ‘Service Brake System’ ‘Skid Limit’ a Service Brake 
Effectiveness Test Conditions test must be conducted applying the brakes on all  ‘Axles’ on both the trailer and the towing vehicl e such that the 
computed retardation of the trailer is within 0.05 m/s
2 of that of the 
towing vehicle.  
22.4.2.4. The computed retardation must be derived from tests of each vehicle braked alone comparing the  ‘Control Signal’ at the truck to trailer 
coupling with the  retardation achieved.  
22.4.2.5. The test must be conducted using the General Test Conditions of part 10 and the generally in accordance with the particular conditions of part 11. Clause 11.2 need not be complied with. 
22.4.2.6. The test result must be reported as the value o f the indicated retardation 
force for each ‘ Axle’ divided by the greatest of the ‘ Axle’ retardation 
forces at which an  ‘Established Retardation Coefficient’ of 0.45, 
calculated with  ‘Total Combination Mass’ held equal to  ‘Gross Trailer 
Mass’,  can be achiev ed without wheel lock.  
22.4.2.6.1. In the case of ‘ S-Cam’ air ‘ Brake Systems’ the overall effect of changing 
actuator and slack adjuster sizes can be simulated by individually adjusting the air pressure to each ‘ Axle’.   DRAFT  Australian Design Rule 38/05 Trailer  Brake Systems  26 
 
   
 23. ALTERNATIVE STANDARDS  
23.1. The technical requirements of  the United Nations Regulation No. 13 – 
UNIFORM PROVISIONS CONCERNING THE APPROVAL OF 
VEHICLES OF CATEGORIES M, N AND O WITH REGARD TO BRAKING, incorporating the 11 series of amendments, are deemed to be equivalent to all  technical requirements of this s tandard, except  for the 
requirements of : 
23.1.1. Clause 7.1.4, in the case of trailers, other than ‘ Pig Trailers ’ that are not 
‘Converter Dollies ’; 
23.1.2. Clause 7.2.1, in the case of  trailers with more than three ‘Axles’  in an 
‘Axle Group’ ; 
23.1.3. Clause 7.2.2, in the case of trailers with more than three ‘Axles’ , or 
trailers without air suspension ; 
23.1.4. Clause 7.2.3, in the case of trailers equipped to tow another trailer with 
an ‘ATM’ greater than 4.5 tonnes ; and  
23.1.5. Clauses 9.2 to 9.4, in the case of trailers with an ‘ATM’ greater than 4.5 
tonnes .  DRAFT  Australian Design Rule 38/05 Trailer  Brake Systems  27 
 
   
 TABLE 1  
GROUP ‘AXLE LOAD’  LIMITS  
 
Number of ‘ Axles’  
 in ‘Axle Group’  Tyre Type “a” and  
Configuration  Group ‘Axle Load’  
Limit (tonnes)  
1   
 S 6.0 
 D 9.0 
 W1  6.7  
 W2 7.0  
 D 10.0 (RFS)  
2    
 S S 11.0 
 S D 13.0 
 W 1 W 1 13.3  
 D D 16.5 
 W2 W 2  14.0  
 D D   17.0 (RFS)  
3    
 S S S  15.0 
 D D D  20.0 
 W1 W 1 W 1 or W 2 W 2 W 2 20.0 
 D D D 22.5 (RFS)  
4   
 S S S S  15.0 
 W1 W 1 W 1 W 1 or D D D D 20.0 
 D D D D  27.0 (RFS) (PBS)  
 
Tyre Type “a”:  
 S Single tyre per wheel  
 D Dual tyres per wheel  
 W 1  ‘Wide Single Tyre’ (375 to 450 mm width)  
 W 2  ‘Wide Single Tyre’ (over 450 mm width)  
 RFS ‘Road Friendly Suspension’  (Note: for information only. Not part of this 
standard).  
 PBS ‘Performance Based Standards’  approved vehicle  as defined under 
Division  3 of the Heavy Vehicle (General) National Regulation (Note: for 
information only. Not part of this standard)  
 DRAFT  Australian Design Rule 38/05  Trailer  Brake Systems   28 
 
   
 TABLE 2  
BRAKE CHAMBER RATED VOLUMES  
 
Brake c hamber type (nominal area 
of piston in square inches)  Stroke  
(inches ) Rated V olume  
(ml) 
Type 9  ≥ 1.75  
≤ 2.10  409 
Type 12  ≥ 1.75  
≤ 2.10  491 
Type 14  ≥ 2.25  
≤ 2.70 655 
Type 16  ≥ 2.25  
≤ 2.70  753 
Type 18  ≥ 2.25  
≤ 2.70  819 
Type 20  ≥ 2.25  
≤ 2.70  884 
Type 24  ≥ 2.50  
≤ 3.20  1097 
Type 30  ≥ 2.50  
≤ 3.20  1458 
Type 36  ≥ 3.00  
≤ 3.60  2212 DRAFT  Australian Design Rule 38/05  Trailer  Brake Systems   29 
 
   
    
DRAFT  Australian Design Rule 38/05  Trailer  Brake Systems   30 
 
   
  
 
   
DRAFT  Australian Design Rule 38/05  Trailer  Brake Systems   31 
 
   
 USE OF TRAILER COMPRESSED AIR BRAKE TEST RIG  
 
FIGURE 3 – CALIBRATION OF TEST RIG  
 
FIGURE 4 – TESTING THE TRAILER  
 
NOMENCLATURE  FOR FIGURES 3 AND 4  
A = supply connection with single check valve and regulator set at 650 kP a 
CF  = trailer brake actuator  
L  = coupling hose, 13 mm nominal bore and 2.5 metres long 
M  = pressure gauge  
O  = orifice (see clause 16.4) 
R1  = reservoir of not less than 30,000 ml  
R2  = calibrating vessel of 800 ± 5 ml  
RA  = shut off valve  
TA  = coupling head -  supply (emergency)  
TC  = coupling head -  control (service)  
TOA  = transducer point for timing inlet to brake actuation  time 
TOR  = transducer point for timing inlet to brake release time  
T1  = transducer point for calibration at end of R2 reservoir  
T2 = transducer point for testing rear tow coupling of trailer  
T3  = transducer point for testing trailer  
V  = brake control valve   
 
DRAFT  Australian Design Rule 38/05  Trailer  Brake Systems   32 
 
   
 FIGURE 5 – EXAMPLE ELECTRIC ‘ CONTROL LINE’ TEST RIG  
 
 
NOMENCLATURE  FOR FIGURE 5  
ECL  =  Electric Control Line corresponding to ISO 7638  
SIMU  =  Simulator of Byte 3,4 of EBS 11 according to ISO 11992- 2:2003 including its Amd -1 
   2007 with output signals at start, 65 kPa and 650 kPa  
A =  Supply connection with shut -off valve  
C2 =  Pressure switch to be connected to the brake actuator of the trailer, to operate at 75  
   per cent of the asymptotic pressure in the brake actuator CF  
CF =  Brake cylinde r 
M =  Pressure gauge  
PP =  Pressure test connection  
TA =  Coupling head, supply line  
VRU  =  Emergency relay valve  
DRAFT  Australian Design Rule 38/05  Trailer  Brake Systems   33 
 
   
 APPENDIX 1  
Additional r equirements  for t railers  (over 4.5 tonnes ‘ATM’) f itted 
with a ‘Variable Proportioning Brake System’  
1. Requirements  
1.1. Trailers fitted with a ‘Variable Proportioning Brake System’ must  have 
markings affixed in a visible position on the trailer in indelible form and 
containing the following information:  
1.1.1. Where the ‘ Variable Proportioning Brake System’  consists of a device 
mechanically controlled by the suspension of the trailer, the useful travel (recommended units of mm) of the device between the positions corresponding to ‘ UTM’  and ‘ GTM’, as well as any further information to 
enable the setting of the d evice to be checked in service.  
1.1.1.1. Where the ‘ Variable Proportioning Brake System’  consists of a device 
controlled via the suspension of the trailer by any other means , the 
information necessary to enable the setting of the device to be checked in service.  
1.1.2. Where the ‘ Variable Proportioning Brake System’  consists of a device 
which modulates the air pressure in the brake transmission, the ‘Axle’  
load(s) (recommended units of kg) corresponding to the ‘UTM’ and ‘GTM’  
for the ‘Axle(s)’ which control(s) the device and the corresponding nominal inlet and outlet pressures (recommended units of kPa) of the device, as well as any further information to enable the setting of the device to be checked in service. The inlet pressure must be not less than 80 per cent of the maximum design inlet pressure, as declared by the trailer manufacturer.  
1.2. Trailers fitted with an electronically  controlled ‘ Variable Proportioning 
Brake System’  (including as part of a ‘Vehicle Stability Function’), that 
cannot fulfil the requirements of clause 1.1 of this appendix above , must  
have a self -checking procedure of the functions which influence brake force 
distribution.  
1.3. Each ‘Unique’  trailer ‘Service Brake System’  must be shown by either 
testing in accordance with par ts 10 and 11 (excluding clause 11.2)  of this 
standard , or by calculation based on data for ‘ Approved’ components using 
the formula in clause 17.3.2, to develop an ‘ Established Retardation 
Coefficient’  of at least 0.45, for at least one ‘Control  Signal ’ (measured at 
the ‘Control Line’  coupling) not exceeding 0.8 ‘E’ (520 kPa in the case of a 
pneumatic ‘Control Line’ ), when at ‘UTM’.  
1.3.1. Linear i nterpolation of data obtained from  tests conducted in ‘Control  
Signal ’ increments not exceeding 0.2 ‘E’ may be used  to demonstrate 
compliance with this clause . 
1.3.2. Trailers equipped with both pneumatic and electric ‘Control Lines’  must  
satisfy the requirements of this clause for each  ‘Control Line’ . In the case of  
an additional electric ‘Control Line’ , the pressure in the ‘Control Line’  is the 
pressure corresponding to the transmitted digital demand value in the electric ‘Control Line’ , according to ISO  11992:2003 including ISO 
11992- 2:2003 and its Amd.1:2007. DRAFT  Australian Design Rule 38/05  Trailer  Brake Systems   34 
 
   
 2. Example Markings  
2.1. An example of markings for a mechanically contr olled device in a trailer 
fitted with a compressed air ‘ Brake System’ that meets clause 1.1.1 of this 
appendix  is shown below. 
Control data  Vehicle 
loading  Axle No. 2 
load at 
the ground  
[kg] Inlet 
pressure  
 
[kPa]  Nominal 
outlet 
pressure [kPa]  
 Laden  
 Unladen  7000 
 
2000 600 
 
600 600 
 
240 
 
2.2. An example of markings for an air pressure controlled device in a trailer 
fitted with a compressed air ‘Brake System’  that meets clause 1.1.2 of this 
appendix is shown below. 
Control data  
 Vehicle 
loading  Axle No. 2 
load at the ground  
[kg] Suspension 
Pressure [kPa]  Nominal 
outlet pressure 
[kPa]  
Inlet pressure 
[kPa]   600  Laden  
 Unladen  
 7000 
 
2000 300 
 
100 600 
 
240 
DRAFT  Australian Design Rule 38/05  Trailer  Brake Systems   35 
 
   
 APPENDIX 2  
Performance and installation  requirements for ‘ Antilock System s’ 
fitted to t railers with an ‘ATM’ greater than  4.5 t onnes  
1. Performance requirements  
1.1. The ‘Brake System’  of trailers equipped with an ‘ Antilock System ’, must : 
(a) Comply with the requirements of c lauses 7.1.3 to 7.1.8 of  this AD R with 
the ‘Antilock Systems ’ operational and in the event of an y one  electrical 
failure of the  ‘Antilock System ’; and  
(b) Be capable of developing, including by actuation through a ‘Control 
Line’  connect ed to a towing vehicle, an ‘Established Retardation Co-
efficient’  of at least  that required  for the ‘Emergency Brake System’ in 
part 8  of this ADR , in the event of any one failure of the ‘ Antilock 
System ’. 
1.2. At speeds exceeding 15 km/h the wheels on the  ‘Axle(s)’  specified in clause 
2.1 of this appendix  must remain unlocked when a  ‘Cont rol Signal’  of 
1.0 ‘E’ (650 kPa) is suddenly applied from an initial speed of 40 km/h +5 to -1 km/h and from an initial speed of at least 80 km/h on a road surface 
having approximately uniform surface friction on both sides of the trailer . 
1.2.1. This test is to be performed  according to the general test conditions of 
part 10 with the trailer laden to both  ‘Lightly Laden Test Mass’  and 
‘Maximum Loaded Test Mass’ . 
1.2.2. Brief periods of locking of the wheels are allowed, but stability must not be affected.  
1.3. The operation of an  ‘Antilock System ’ must not be adversely affected by 
magnetic or electric fields.  
2. Installation r equirements  
2.1. An ‘Antilock System ’ complying  with clause 1 of this appendix  must be 
fitted to: 
2.1.1. each ‘Single Axle’ ; 
2.1.2. at least one ‘Axle’  in any  ‘Tandem Axle Gr oup’; 
2.1.3. at least two  ‘Axles’  in any  ‘Triaxle Group’ ; 
2.1.4. at least three ‘Axles’  in any  ‘Axle G roup’  with four ‘Axles’ . DRAFT  Australian Design Rule 38/05  Trailer  Brake Systems   36 
 
   
 APPENDIX 3  
‘Vehicle Stability Function’  requirements  for category TD t railers   
1. Definitions  
1.1. ‘Vehicle Stability Function ’ means an electronic control function for a 
vehicle which improves the dynamic stability of the vehicle.  
1.2. A ‘V ehicle S tability Function’  includes one or both of the following:  
(a) ‘Directional C ontrol ’; 
(b) ‘Roll-over C ontrol ’. 
1.3. Control functions within a ‘V ehicle S tability F unction’ : 
1.3.1. ‘Directional control ’ - means a function within a ‘ Vehicle S tability 
Function’  that assists the driver, in the event of understeer and oversteer 
conditions, within the physical limits of the vehicle in maintaining the 
direction intended by the driver in the case of a power -driven vehicle, and 
assists in maintaining the direction of the trailer with that of the towing 
vehicle in the case of a trailer.  
1.3.2. ‘Roll-over control ’ - means a function within a ‘V ehicle S tability F unction’  
that reacts to an impending roll -over in order to stabilise the power -driven 
vehicle or towing vehicle and trailer combination or the trailer during 
dynamic  manoeuvres within the physical limits of the vehicle.  
1.4. ‘Automatically Commanded Braking ’ and ‘Selective Braking’  events : 
1.4.1. ‘Automatically Commanded Braking’ – means a function within a complex electronic control system where actuation of the braking system(s) or brakes of certain axles is made for the purpose of generating vehicle retardation with or without a direct action of the driver, resulting from the automatic evaluation of on board initiated information. 
1.4.2. ‘Selective Braking’ -  means a function within a complex electronic control 
system where actuation of individual brakes is made by automatic means in which vehicle retardation is secondary to vehicle behaviour modification.  
2. Functional r equirements  
2.1. For each category TD  trailer  required to be equipped with a ‘ Vehicle 
Stability Function’  as defined  above, the following shall apply:  
2.1.1. In the case of ‘D irection al Control ’ the function must  have the ability to 
automatically control individually the speed of the  left and right wheels on 
each ‘A xle’ or an ‘A xle’ of each ‘Axle G roup’  by ‘Selective Braking ’ based 
on the evaluation of actual trailer behaviour in comparison with a determination of the relative behaviour of the towing vehicle.  
2.1.2. In the case of ‘R oll-over Control ’ the function must  have the ability to  
automatically control the wheel speeds on at l east two wheels of each ‘Axle’ 
or ‘Axle G roup ’ by ‘S elective B raking ’ or ‘A utomatically C ommanded 
Braking ’ based  on the evaluation of actual trailer behaviour that may lead to 
roll-over.  DRAFT  Australian Design Rule 38/05  Trailer  Brake Systems   37 
 
   
 2.1.3. The ‘Vehicle Stability Function ’, including the  ‘Roll-over Control ’ function, 
does not need to be operational during system initialisation, at trailer 
operating speeds below 2 0 km/h , when the trailer is being reversed,  or if 
disabled by an operator according to clause 2.1.3.1 below. 
2.1.3.1. A separate and distinct means (for example an off road mode selector/switch  
on the trailer ) may be provided to enable an operator to disable  the ‘ Vehicle 
Stability Function ’ for trailer operating speeds up to 40 km/h.  
2.2. To realise the functionality defined above a ‘Vehicle Stability Function’  
must  include, in addition to ‘A utomatically C ommanded B raking ’ and 
where appropriate ‘Selective B raking ’, at least the following:  
2.2.1. The determination of actual trailer behaviour from values of the vertical force on the tyre(s), or at least lateral accelerat ion and wheel speeds. Only 
on-board generated information may  be used. If these values are not directly 
measured, the ‘Manufacturer’  must supply to the  ‘Administrator’  sufficient 
evidence of the appropriate correlation with directly measured values under all driving conditions (e.g. including driving in a tunnel). 
2.3. Trailers equipped with an electric ‘Control Line’  must , when electrically 
connected to a towing vehicle with an electric ‘Control Line’ , provide the 
information "VDC active" via the data communications part of the electric ‘Control Line’  when the ‘Vehicle Stability Function’ is  in an intervention 
mode. Interventions of the ‘Vehicle Stability Function’ used in any learning process to deter mine the trailer operational characteristics must not generate 
the above information (note: VDC or Vehicle Dynamic Control, as defined 
within ISO 11992- 2:2003 including Amd.1:2007, is defined within this 
national standard as a ‘Vehicle Stability Function’) . 
 DRAFT  Australian Design Rule 38/05  Trailer  Brake Systems   38 
 
   
 APPENDIX 4  
Electrical  requirements for all trailers ( over 4.5 tonnes  ‘ATM’)  incorporating 
an electric ‘Control Line’ , an ‘Antilock System’,  or a ‘Vehicle Stability Function’  
1. Electrical supply system requirements  
1.1. Each trailer must be fitted at the front with a  special connector conforming 
to ISO  7638- 1:2003 configured for 24 volt operation or ISO 7638 -2:2003 
configured for 12 volt operation.  The ‘Vehicle Stability Function’ and the 
‘Antilock Systems’  of the trailer must be abl e to be simultaneously powered 
by an  electrical supply  from a towing vehicle  through this connect or. 
1.2. Each  ISO 7638 connector1 must be wired to have the following functions:  
Contact  1 +ve high current trailer solenoid valve supply ; 
Contact  2 +ve low current  trailer electronic unit supply ; 
Contact  3 -ve low current trailer electronic unit supply ; 
Contact  4 -ve high current trailer solenoid valve supply ; and  
Contact  5 trailer warning signal, switched to - ve (e.g. contact  3 or contact  4) 
upon fault detection as  well as for the signal check  required by clause 1.4 
below . 
1.3. The continuous current capacity of the electrical conductive material 
between each contact of an ISO 7638 connector at the front of a trailer and 
the brake systems ( e.g. electr onic control unit (s), solenoid val ves) which 
current flows to or from within the trailer , must be at least the following : 
 12 volt connector  24 volt connector  
Contact  1 20 amps  10 amps  
Contact  2 4 amps  2 amps  
Contact  3 6 amps  3 amps  
Contact  4 20 amps  10 amps  
Contact  5 2 amps  1 amp  
1.4. Each  trailer equipped with an ‘Antilock System’ , must connect contact  5 of 
the applicable electrical connector to - ve (e. g. contact  3 or contact  4) for at 
least 2 seconds once  initially energised , and if  no fa ult / defect is present , 
then disconnect contact 5 from - ve at this time or before  the trailer reaches a 
speed of 15 km/h.  
  
                                                 
1 ISO 7638 connector means an ISO 7638- 1 (24 volt) connector or an ISO 7638- 2 (12 volt) 
connector.  DRAFT  Australian Design Rule 38/05  Trailer  Brake Systems   39 
 
   
 1.5. Each  trailer equipped with a ‘Vehicle Stability Function’ and/or an ‘Antilock 
System’ , must connect contact  5 of the applicable electrical connector to - ve 
(e.g. contact  3 or contact  4) when ever: 
1.5.1. There is a break in the supply of electricity to a ‘Vehicle Stability Function’ 
and/or an  ‘Antilock System’  and any electrical failure of a ‘Vehicle Stability 
Function’  and/ or an ‘Antilock System’ , other than a failure of one or all of 
the electrical conductors between contacts  3, 4 and 5 on the electrical 
connector and the vehicle stability/ antilock control module;  or 
1.5.2. The supply voltage to the trailer falls below a value nominated by the 
manufacturer at which the prescribed requirements for any of the braking 
functions required by clause 7.2 of this standard can no longer be met . 
1.6. Each  category TD trailer  other than a ‘Converter Dolly’ , which is equipped 
with a ‘Vehicle Stability Function’ , must also connect contact  5 of the 
applicable electrical connector to - ve (e.g. contact 3 or contact 4) , if/when  
its ‘Vehicle Stability Function’ is disabled in operation above 20 km/h , by a 
means satisfying  clause 2.1.3.1 of APPENDIX 3.  
1.7. The power supply  transmitted  through an ISO 7638 connector must be used 
exclusively for braking and running gear functions and that required for the transfer of trailer related information not transmitted via an  electric ‘Control 
Line’ . 
1.7.1. However, in all cases, whenever power transmitted  through an ISO 7638 
connector is used for the functions defined in this clause above, the braking system must have priority and be protected from an overload external to the 
braking system. This protection must be a function of the braking system.  
1.7.2. The p ower supply for all other functions must use other measures.  
2. Electric 
‘Control Line’  requirements  
2.1. In the case of a trailer equipped with an electric ‘Control Line’ : 
2.1.1. The communications  via the electric ‘Control Line’  must  conform to 
ISO 11992- 1:2003 and ISO 11992- 2:2003 including its amendment 1:2007 .2 
2.1.2. The electric ‘Control Line’  must  be a point -to-point type using a  seven pin 
(or tube) connector in accordance with ISO 7638- 1:2003 or ISO 7638 -
2:2003;  as per which, contact 6 must be wired  for the CAN_H signal  and 
contact 7 must be wired  for the CAN_L signal.  
2.1.3. The electric ‘Control Line’  must meet the requirements of 
ISO 11992- 1:2003 including:  
(a) The wiring must be an unshielded twisted pair ; and 
(b) The maximum cable length of the electric ‘Contr ol Line’  within the 
trailer must not exceed 18 m and the bus capacitance of the cable must not exceed 2.9 nF, except where otherwise permitted  by clause 2. 3 of 
this appendix below.  
                                                 
2 These include specific CAN voltage range requirements for 12 volt and 24 volt nominal voltage 
systems.  DRAFT  Australian Design Rule 38/05  Trailer  Brake Systems   40 
 
   
 2.1.4. The message "illuminate stop lamps" must be transmitted by the trailer via 
the electric ‘Control Line’  when the trailer ‘Service Brake System’  is 
activated during ‘Automatically Commanded Braking’ initiated by the trailer. However, the signal may be suppressed, when the retardation generated is less than 0.7  m/s
2. 
2.1.5. The message "il luminate stop lamps" must not be transmitted by the trailer 
via the electric ‘Control Line’  during ‘Selective Braking’ initiated by the 
trailer (note: during a ‘Selective B raking ’ event, the function m ay change to 
‘Automatically C ommanded B raking ’). 
2.2. The da ta contacts of an  ISO 7 638 connector incorporating an electric 
‘Control Line’  must  be used to transfer information exclusively for braking 
(including the  ‘Vehicle Stability Function’ and ‘Antilock System’ ) and 
running gear (steering, tyres and suspension) functions as specified in 
ISO 11992- 2:2003 including its a mendment 1:2007. 
2.2.1. The braking functions have priority and must be maintained in the normal and failed modes. The transmission of running gear information must not delay braking functions. 
2.3. The overall  length of the  electric ‘Control Line’  installed with in a trailer 
may exceed the 18  m permitted by ISO 11992- 1:2013, where a device (e.g. 
CAN repeater) is installed to amplify and repeat messages in such a way that all  communication s throughout  the electri c ‘Control Line’  otherwise 
conform with  ISO 11992 -1:2003 and ISO 11992- 2:2003 including its 
amendment 1:2007. 
2.4. A message routing device/ function (e.g. CAN router) conforming to 
ISO 11992- 2:2003, paragraph 6.3 (Message R outing ), is required for all 
trailers incorporating electric ‘Control Line’  through which messages are 
distributed between more than two electronic nodes (e.g. trailers for which 
multiple control units are used to provide the braking functions required by  
clause 7. 2 of this standard) . Such  a device/ function is  necessary to sat isfy 
the point -to-point type requirement for the  electric ‘Control Line’  between 
electronic devices . 
3. Additional requirements for all t railers equipped to tow another trailer 
with an 
‘ATM’  greater than 4.5 tonnes  
3.1. Except as provided in clause 3.1.1 below, e ach trailer (including a ny 
‘Converter Dolly’ ) equipped to tow another trailer with an ‘Aggregate 
Trailer Mass (ATM) ’ greater than 4.5 tonnes , must be fitted at the rear with  
a connector co nforming to ISO  7638- 1:2003 and meeting  the requirements 
of clause 1.2 of this appendix .3  This connector must be configured to 
distribute a 24 volt  electrical supply, received via a connector in accordance 
with ISO 7638- 1:2003 at the front of the trailer , to a ‘Vehicle Stability 
Function’ and/or the ‘Antilock Systems’  of a towed traile r.4 
                                                 
3 Where a seven contact ISO 7638 connector is used at the rear of a trailer equipped t o tow another 
trailer, any electric ‘Control Line’  wired to contacts 6 and 7 of this connector must also meet 
clause 2 of this appendix.  
4 This does not prevent ISO 7638- 2 connectors and through wiring from also being fitted to 
distribute a 12 volt nominal supply voltage to a towed trailer.  DRAFT  Australian Design Rule 38/05  Trailer  Brake Systems   41 
 
   
 3.1.1. A ‘Semi -trailer’  that is equipped with a ‘Fifth Wheel Coupling’  towards the 
rear (i.e. an A -trailer  / Lead -trailer ) and is not designed for use in ‘Road 
Train’  combinatio ns, may be fitted with  a connector  conforming to 
ISO 7638- 2:2003 in place of the 24 volt  connector  otherwise required 
above . This connector must be configured to distribute a 12 volt  electrical 
supply, received via a connector in accordance with ISO 7638- 2:2003 at the 
front of the trailer,  to a towed trailer.  
3.2. The continuous current capacity of the electrical conductive material  
through which current flows between  the contacts of the ISO 7638 
connector s at the front and rear of a trailer equipped to to w another trailer 
with an ‘ATM’ greater than 4.5 tonnes , must be at least the following:  
 12 volt or 24 volt 
connector  
Contact 1  20 amps  
Contact 2  4 amps  
Contact 3  6 amps  
Contact 4  20 amps  
Contact 5  2 amps