Trucks and Stoppping Distances on the Road
On the Arrive Alive website we report daily on accidents involving all vehicle types. There are unfortunately many “multiple vehicle accidents” where we find collisions between trucks, minibuses, bakkies, cars etc. We could argue that a greater appreciation and understanding between drivers of the different modes of transport of the braking distances required for the different vehicles could be an important requirement for safer driving behaviour and increased road safety.
We have offered advice to all road users about “sharing the road”. This is of importance especially in light of the fact that there is a lack of understanding amongst motorists of the braking distance required by truck drivers. Motorists tend to ignore the fact that truck drivers need a much longer distance to bring their vehicles to a stop – and truck drivers need to ensure that their vehicles are indeed capable of stopping within the required distance.
Fleetwatch Magazine offered to assist with information on the stopping distances of trucks and has given permission to share their expertise on the Arrive Alive website.
It’s worth repeating - stopping is just as vital as moving forward. No owner of any truck would like to be in an aircraft that runs out of runway on take-off. Why then do they let their drivers operate trucks that run out of stopping distance? If you are in trucking and do not understand the importance of stopping distance – the runway distance required to come to a halt – then why are you in this business asks our technical correspondent Dave Scott?
The analogy of an aircraft that fails to take off and a truck that fails to stop are intertwined. An aircraft takeoff failure is a cascade of events – too few hours between bottle and throttle, load, poor judgment and over-confidence, mechanical defects, insufficient power, badly conducted flight pre-checks, unfavourable weather conditions, inadequate training, surface rolling resistance and gradients. In the case of an aircraft, each influencing factor lengthens the take-off distance but in the case of stopping a truck, the closing gap just gets longer when it should be shorter.
Stopping distances are critical
Trucks need distance to stop in an emergency but unthinking motorists on freeways take the gap and fill it. Five to 10 metres between a car bumper and a truck at 80kph is just not enough.
Table 1 (below) shows a Utopian scenario at 80kph with everything in ‘perfect working order’ on a good surface with excellent weather/ visibility and using wide-awake drivers:
- Scenario 1 is a sports car fitted with an ABS braking system.
- Scenario 2 is a medium truck with vacuum/hydraulic brakes and no ABS system but everything is mechanically correct. However, braking efficiency is not as good as the sports car.
Medium trucks are driven like passenger cars and at 8,5t GVM, they can wreak havoc in an emergency due to the kinetic energy generated. The medium truck takes 40% longer to stop than the sports car. Do drivers really think of this?
Up the stakes
Now to reality in Table 2. Let’s up the stakes to 120kph. Remember that all trucks under 9t GVM are allowed to travel at 120kph under Road Traffic Act Regulation 293 (1).
- At 120kph, a perfectly-driven ABS equipped sports car takes longer to stop than in the scenario sketched out in Table 1.
- Scenario 2 here introduces badly maintained brakes at 30% efficiency and a tired driver with a 2-second reaction time. The brakes have heat-faded and loadsensing is not functioning.
At 120kph, the 8,5t GVM truck takes 124% longer to stop than the car. And how many 56t GCM rigs do you notice that far exceed the 80kph limit where the same laws of gravity apply?
Driver reaction at 120kph is an absolute factor where one second's travel is 33,33m. But because there is no traffic enforcement at night, everyone likes to up the speed level when even excellent headlights on a dipped beam reach a max of 60m. The point is that on a dipped beam at 120kph at night, if you see it you will hit it!
Research conducted on SA roads in 1995 is more relevant than ever 14 years later. A comprehensive report, 93/336 dated July 1995 titled ‘The influence of night driving and wet weather conditions on driver and vehicle abilities’, prepared for the Department of Transport (DoT) by BKS Inc. of Pretoria, comments that: ‘During the night, the frequency of collisions is three to four times higher than during the day.....darkness has an adverse effect on road safety, as both the severity and the frequency of collisions increase during this period.’
This is verified in a histogram published in the report covering a five year period titled ‘Association between frequency of collisions and light’. A fair estimate would increase the odds today – the chance of an accident at night is at least now four to five times greater than in daylight.
Bring in the OHS Act
If reaction times are so critical, why are so many driver controls in the cab - which is an OHS Act declared workstation - in such a sloppy mess? Poor reaction times resulting from driver fatigue are only compounded in loose linkages starting at the brake pedal and then all over a vehicle combination right down to slack adjusters that are sometimes fastened with wire.
Is it not time to call in factory inspectors to enforce the conditions of the OHS Act in a truck cab? Road traffic enforcement agencies cannot seem to get this one right and perhaps there’s another approach to vehicle safety that we haven’t tried.
It’s all about how much runway there is to play with. On the road, it’s a constantly changing scenario but for an aircraft, it’s pre-determined. You don’t take off when someone else occupies the airstrip and runway length is a set figure. Truck driving does not allow those parameters, so reaction times and stopping distances are therefore vital.
We’ve seen Government ministers attend a mining accident funeral that is statistically small by comparison to the daily slaughter on our roads. Where are these same Ministers when there’s a multiple death road accident?
I repeat: If you are in trucking and do not understand the importance of stopping distance – the runway distance required to come to a halt – then why are you in this business?
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Load sensor
Connecting the load sensor is pretty much a basic if you want to achieve an effective stopping distance. This one is disconnected
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Sloppy controls
The inside of this truck cab (both above) on a truck pulled in for testing during a recent FleetWatch Brake & Tyre Watch exercise was a shocker. If this is an acceptable OHS Act needs re-defining - or more likely, enforcing. Truck owners would never accept this for their personal transport so how can they allow it to represent their business ethics? Forget about stopping distance on such a rig as it also had no brakes to talk of.
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Airtanks with oil
The air-pressure drain valve on this air reservoir has released black, dirty oil that sprayed onto the exhaust pape and the floor. Obviously the compressor is pumping oil into the braking system.
This means a faulty compressor combined with brake valves that don't provide the required reaction times.
Stopping distance on this rig? You've got to be kidding. It's an accident in the waiting.
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A word of appreciation for FleetWatch who provided the content.
