109 The defendants do not agree that the braking system on the truck would, or did, drop to a point where the brakes could not bring the truck to a halt. They submit that there was no evidence that the engine stopped and all systems of braking failed.
110 According to Mr Russell Smith, if only half the braking capacity of the truck was available, and the engine was not running, it would be "virtually impossible" to halt the laden truck on a 1 in 5 decline. It will be recalled from the agreed facts, set out in these sentencing reasons, that the haul road had an average gradient of 1 in 5, with some sections being almost 1 in 4.
111 With regard to the condition of the brakes at the time of the accident I have already found that the front brake air circuit was affected by three air leaks. The split in the air hose, which carried air from the front brake air reservoir to the relay valve, caused a loss of air pressure. A further loss of air pressure was caused by the leak in the retarder valve (which linked into the air pressure system). The leak in the retarder valve was described by Mr Lewis from ABC as a "large air leak, at 20 psi". Air pressure was also leaking through the front brake intensifier (the converter) because of the worn hydraulic seal. In addition to those faults, the two front brakes were incapacitated because of the very low brake fluid level in the front brake reservoir, and the RHC brake was inoperable (in that it could not function effectively) because of the presence of the oil mixture. The consequence of these various faults in combination was that the truck prior to the accident had only three effective brakes. It follows that if, for some reason, the retarder on the truck disengaged on the descent then Mr Smith had only half the brakes at his disposal in order to bring the truck to a halt. Utilising the park brake would not have assisted him since, as I have found, it was so out of adjustment that it would have provided no braking force on the haul road.
112 The conclusion which inevitably follows from these matters is, taking into account Mr Smith's finding outlined above, that if the engine of the truck had stopped on its descent (for whatever reason) and the retarder disengaged, then with only three effective brakes and the loss of air pressure, the truck could not have been brought to a halt on the haul road and would have been in a runaway condition.
Did the engine stop?
113 The next issue for consideration is whether the engine stopped, for whatever reason, prior to its plunge over the embankment.
114 It was Mr Sunol's conclusion that the engine had stopped prior to the accident. His conclusion followed his physical examination at Gough & Gilmour of a number of component parts of the engine. He examined the radiator and the fan and noted that the damage to both parts was light and not extensive. This minimal damage to the radiator, for example, Mr Sunol said, was consistent with it not turning. It was put to him in cross-examination that the small amount of damage could have been the result of a short period of time in which the radiator fan touched the radiator fins. Mr Sunol rejected this proposition saying:
I was trying to explain even for a short period of time, the impact and the lack of damage to the aluminium motor fan hub and other components are consistent with it not turning - because if you look at the fan hub in particular, it is, there is zero damage. When you look at the fan propeller with consideration, it is doing even at idle 11 revolutions per second, even if it touches for a fraction of second a tenth of a second, then I would expect to see every fan blade tip broken off.
115 Mr Richardson, one of the defendants' experts, estimated that the speed of the truck immediately before it went over the embankment was about 39 kmh. Mr Russell Smith agreed in cross-examination that a truck travelling at a speed in the vicinity of 45 to 50 kmh meant that the retarder was not working.
116 In written submissions on the issue the prosecution said:
The starting point is to accept that at the time the Truck struck the concrete blocks at the edge of the embankment and then became airborne it was travelling at about 39km/h. The Defence witnesses accepted that the Truck could not have reached that speed with the retarder on.
117 Mr Richardson did not provide any basis for his estimate that the truck's speed was, "about 39kmh". Nevertheless there was no dispute that the launch speed of the truck was approximately 39 kmh, and that at this speed the retarder could not have been engaged. As to the other defence witnesses who, according to the prosecution's submission, accepted that the truck could not have reached a speed of 39 kmh with the retarder on, only Mr Smith gave evidence of a particular speed at which the retarder on the truck would disengage. He said it was between 45 to 50 kmh.
118 An inference is also available from the evidence that the truck's rate of descent down the haul road was rapid. Mr Warden, who gave an eye-witness account, described the truck as pushing the concrete blocks through the embankment and launching into the air before nose-diving into the embankment. He saw rocks and dirt being thrown up as the truck "ploughed" through the rocks and the concrete barrier. This description suggests that the truck was travelling at a fast speed immediately prior to going over the embankment.
119 The minimal damage sustained to the radiator and the fan as observed by Mr Sunol, and the rapid speed of the truck's descent, suggest that the engine had stopped prior to its plunge over the embankment. According to Mr Russell Smith, the retarder would be non-functional should the engine cease to operate. With the retarder not functioning, the truck was reliant on its service brakes to bring it to a halt. If the brakes were not able to stop the truck, it would be in a runaway condition.
120 The retarder would cease to operate for other reasons. It would cease to operate if Mr Smith had his foot on the accelerator and was driving in automatic mode down the haul road. This contingency may be discounted, however, because of the evidence concerning the blueing of the left-hand rear disc. In my view the effect of that evidence was that Mr Smith was attempting to apply the service brakes on the haul road (and therefore would not, at the same time, have had his foot on the accelerator) immediately prior to the truck's plunge over the embankment. I deal now with the evidence concerning the blueing of the left-hand rear disc.
121 The prosecution contended that the heat marks on the disc (and brake pad locating pin) observed by Mr Sunol, meant that the brakes had been applied on the descent and that those brakes were in such a state that they were incapable of bringing the truck to a halt.
122 Mr Sunol's evidence of what he observed in respect of the left hand rear disc and pins was:
a. heat marks on the brake disc and outer brake pad locating pin;
b. the heat marks were located on the brake disc directly underneath the outer brake pad;
c. the outer brake pad had marks on the rear third of the pad which matched up with the heat marks on the outer rear brake pad locating pin;
123 Mr Sunol concluded that the heat marks were "a direct result of the incident". They were not pre-existing marks prior to the incident because of three matters:
a) they would not have been directly underneath the brake pad.
b) they would not have imprinted the brake pad segment on the brake disc.
c) they would have been scuffed off from further use if the heating occurred early.
124 His overall conclusion that the blueing of the disc had occurred at the time of the accident was expressed as follows:
Based on my expert knowledge and experience I concluded heat marks are from the heat energy obtained during braking of Truck 28 as it came down the haul road. At the point in time when Truck 28 went over the embankment and the LHR wheel lost traction to the haul road, then the brake pads would have locked up the wheel and the brake disc would have stopped rotating. The heat marks on the brake disc would have been created at this point in time as the heat energy is unable to be dissipated from underneath the brake pads.
125 In his oral examination Mr Sunol added to his evidence on the issue:
A. Those markings could only have occurred during the descent. That the markings were as a result that when the brake, the brakes were applied during the descent. They were unusual because normal heat marks are throughout the whole circumference. These marks were in an isolated spot under the brake pads which leads me to the conclusion that as the brake disc has heated up and as it's gone over the embankment and lost traction between the tyre and the road the brakes have locked on solid which has prevented the disc from dissipating heat and creating the blue marks.
Q. In that area beneath?
A. Yes. The only area that showed signs of blueing was directly underneath the pads and only in the rear segment of the pad. The front segment of the brake pads did not show signs of heating.
Q. I will just follow the mechanism you have described, you envisaged that the brake rotor became seriously hot in the course of going downhill; correct so far?
Q. That when the vehicle left the road surface at the edge that in the absence then of the friction between the tyre and the road surface the brakes were able to lock the wheel at last?
A. That's correct.
Q. And the heat dissipated from the balance of the disc but could not escape from that area which was enclosed by the brake pads themselves?
A. Yes, that's correct.
Q. And that is what we are looking at here in your view?
A. Yes.
126 Mr Richardson, in his report, expressed some criticism of Mr Sunol's findings. He suggested that additional tests could have been conducted by a metallurgist with regard to the heat marks on the disc. He did not elaborate, however, on why he thought that was necessary. Mr Lewis was asked in cross-examination whether a metallurgist was necessary in order to identify with precision when the heat marks appeared on the pad area. His response was "No ... something I understand as an engineer". He was not questioned further, on that issue.
127 Mr Richardson, in oral evidence, also suggested that it was possible that at the point the truck became airborne the brakes locked on launch (consistent with the prosecution case). Mr Richardson also suggested however that the brakes might have come on suddenly, when the truck was airborne and at that instant the heat caused the blueing to occur. This evidence was advanced no higher than a possibility and therefore does not impact upon Mr Sunol's analysis and findings as to the presence of the heat marks on the disc. I find therefore that the retarder did not disengage because Mr Darren Smith had his foot on the accelerator. Rather, he was attempting, unsuccessfully, to apply the brakes while the truck was descending the haul road at a rapid speed, prior to going over the embankment.
128 The retarder could also disengage because of a mechanical problem caused either by a significant drop in air pressure or because the engine revolutions had exceeded 2,500 rpm or had dropped below 1,200 rpm. That the engine exceeded 2,500 rpm may be discounted because that event was not recorded on the truck's ECU (the truck's "black box"). According to the truck's Operator's Manual:
The retarder will automatically engage when the engine speed reaches 2,500 rev/min and it will disengage at 2,300 rev/min to prevent engine overspeeding.
If the vehicle is approaching an overspeed condition, the retarder is automatically applied at 2,500 rev/min irrespective of the transmission oil temperature. If the overspeed condition occurs the transmission will upshift to 2,700 rev/min and a fault code will be recorded in the ECU for the engine overspeed and/or the transmission temperature.
129 Mr Badior, in cross-examination, was asked about the above extract from the Operator's manual (referred in the evidence as "the book"). The transcript of his evidence records:
Q. And as the book tells us, if it reaches 2,700 revs per minute a fault code will be recorded in the ECU. I just want to ask you about that. You know the ECU to be the on-board computer?
A. That is correct.
Q. And you know, don't you, that examination of the T28 ECU after the accident showed that there was no fault recorded for the last four occasions that the engine had been utilised?
A. That is correct.
130 Mr Russell Smith, in oral evidence, said that if the engine of the truck stopped then the retarder would not function (because the lockup clutch automatically disengages). He was also asked some questions about the pre-existing air leak on the retarder valve and the consequence of the leak on the operation of the retarder. He said:
I assume that it would disable the retarder totally and actually the testing that we did was with the retarder inactive.
131 According to Mr Warden, with the retarder engaged, the truck would normally descend in second gear travelling at about 8 to 10 kmh. With regard to the air leak on the retarder valve, Mr Sunol concluded that it would have caused the retarder to disengage earlier, upon a loss of air pressure, than it otherwise would if there was no air leak. Mr Russell Smith merely assumed that the air leak would, "disable the retarder totally". This evidence does not enable the Court to conclude, with any degree of certainty, that the air leak on the retarder valve caused the retarder to disengage.
132 There was other evidence from which the conclusion may be drawn that the retarder disengaged because the engine had stopped when the truck was descending the haul road. This was the evidence that the truck was travelling at a rapid speed down the haul road (Mr Warden's eye-witness account), Mr Richardson's estimate that the truck was travelling at a launch speed of about 39 kmh (at which speed, it was conceded, the retarder was not engaged), as well as Mr Sunol's analysis and findings that the engine had stopped, based on the condition of the radiator, the fan and other components. Based on this evidence I find beyond reasonable doubt that the engine stopped at some point when the truck was descending the haul road. The effect of this evidence was, as earlier observed, that the truck was totally reliant on its service brakes to slow its speed or bring it to a halt. As the heat marks on the left-hand rear disc suggest, Mr Smith was attempting to apply the brakes while the truck was on the haul road. He was unsuccessful because, as I have found, the service brakes were operating at half capacity. The state of the service brakes at this critical time were such that, with the engine not running, the truck could not be brought to a halt.
133 The defendants criticised Mr Sunol's approach to his investigation of the reasons why the truck became out of control. It was said that Mr Sunol's approach was too narrow, focusing on the truck's mechanical failures and not considering any "human factors" that may have contributed to the truck becoming out of control.
134 One such factor advanced as "not implausible" by the defendants was that Mr Smith may have fallen asleep. A report of Professor Ian Whyte from MediTox Pty Ltd was relied upon by the defendants in support of the contention. Professor Whyte was provided with documents which included the autopsy report of Dr Lyons and a toxicology report of 9 August 2005. With regard to the latter report Professor Whyte noted:
The toxicology report showed no evidence of alcohol but identified diphenhydramine in femoral blood at a concentration of 0.2 mg/l and ibuprofen at a concentration of 5.2 mg/l.
135 Professor Whyte observed that 0.2 mg/l was within the reported therapeutic range of four 50 mg doses per day but he could not say whether this resulted from one acute dose or from chronic multiple dosing. Professor Whyte concluded:
In summary, diphenhydramine in acute doses of 50 mg or more can impair driving. The main deficits are in maintaining position within a lane and reaction time. Psychomotor testing suggests these driving impairments come from decreased vigilance and attention. There is a dose relation with higher doses causing more impairment...
136 In relation to the level of ibuprofen noted in the toxicology report, Professor Whyte found no evidence that it adversely affects driving performance either alone or in combination with other drugs.
137 This evidence provides no support for the defendants' contention that Mr Smith might have been drowsy or further asleep as a result of medication he had taken. The level of diphenhydramine in Mr Smith's blood, Dr Whyte could not say was the result of an acute dose or from chronic multiple dosing. It was only if the level of diphenhydramine was the result of an acute dose that Mr Smith's driving might have been impaired. No evidence was found by Dr Whyte that ibuprofen adversely affects driving performance.
138 The defendants also suggested that it was "not fanciful" that Mr Smith, "had taken a micro sleep and/or had a reduced capacity to react at the time of the incident". The bases upon which this proposition was advanced was that Mr Smith weighed 111 kg, had been at work since 6 am, monotonously driving up and down the haul road with diphenhydramine in his blood, and, because it was June with the temperature likely to have been low, Mr Smith was likely to have had the air conditioner working. These matters, which amount to no more than conjecture, provide no support for the proposition that Mr Smith had taken a micro sleep or otherwise had a reduced capacity to react.
Why did the engine stop?