If there is one ultimate buzzword in Australia’s commercial road transport industry, it’s safety. Arguably the single most important component in that context is the braking system. A new ADR is now giving it a considerable upgrade.
From 1 July, a new Australian Design Rule (ADR 35/04) will come into effect, mandating Antilock Brake Systems (ABS) for medium to heavy-duty trucks sold in Australia. In line with that change, ADR 38/04 will require ABS or a Load-Sensing brake system (LSB) to be fitted to heavy trailers with an Aggregate Trailer Mass above 4.5 tonnes from 1 July 2014 for new vehicle models and 1 January 2015 for all vehicle models.
According to ARTSA Chairman, Dr Peter Hart, the ADR change could mark the start of a new era in commercial road transport – but there are risks to be considered, too.
“Historically, improvements to Australian Design Rules (ADR) for heavy vehicle braking were constrained by the need to maintain interoperability of the wide and varied trailer fleet used in Australia. This limited the industry’s ability to easily adopt new braking technologies. Now we could see the start of a new era for vehicle safety,” he explains.
“As a result, the confirmation of the new trailer brake rule should be welcomed,” he adds – pointing out that the main motivation for the update was to improve the safety of truck and trailer combinations when the trailer is only lightly loaded.
But, if the wrong systems are matched in a combination, imbalances could arise down the line. “The mixing of different brake control technologies on a combination vehicle needs to be done with insight to minimise the risk of poor brake balance occuring. Both ADR 35/04 and 38/04 do not guarantee good brake balance because they apply to single-vehicles only.”
According to Peter, both ABS and LSB have merit; in fact both are needed. “Wheel lock-up is undesirable because a locked tyre looses most of its road following capability,” he explains. “Antilock brakes protect a combination against this. Load-Sensing brakes can improve the brake balance of a combination and thereby reduce the likelihood that the wheels will lock-up during braking when the vehicle is lightly laden.”
ABS is a driver assistance system designed to prevent wheels from locking when the vehicle is braked in an emergency situation. Research has shown that ABS increases the directional stability of heavy vehicles under braking, reducing crash related fatalities and injuries with an estimated effectiveness of between three and eight per cent.
A variable proportioning brake system like LSB, meanwhile, is a simpler, (usually) non-electrical means of adjusting braking to the loaded condition of a trailer by using a pneumatic load-sensing relay valve that changes its maximum brake setting in proportion to a load signal; which is usually the air-suspension bag pressure.
Overall, authorities expect to save a total of 36-57 lives over a period of 30 years for ADR 35 and ADR 38 combined.
However, Dr Hart says there is a downside to the new system. “If Load Sensing brakes are used on only one trailer in a multi-combination, then the brake balance will be poor. The extreme consequence of poor brake balance can be trailer swing or jack-knifing by the trailer without the LSB during moderate or heavy braking.
“The reason is simple. If the braking capability of only one vehicle in a combination is reduced, the other parts will do more of the braking work. The chance that the wheels will lock-up on these other parts is increased, assuming they are also lightly laden.”
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