Prime Mover Magazine


The human factor on emissions

The human factor on emissions

Prime Mover's search for the low carbon trucking solution for road transport operators comes to the most important and most variable factor in reducing carbon emissions, the truck driver.

All of the high level technology involved in truck design and careful consideration of components in order to minimise fuel use can bring a genuine reduction in fuel use. However, if an operator is genuinely serious about bringing down their carbon emission levels and reducing their exposure to any potential future carbon tax, it is the behaviour of the person behind the wheel which has to be just right in order to get the best results.

All of the expensive technology and careful planning will be to no avail if a truck driver has an irresponsible attitude and an aggressive driving style. The effect of many of the technologies detailed in previous articles in this series can be blown out of the water by an irresponsible driver with a heavy right foot.

The human factor, the truck drivers themselves, may be the most important but, in many ways, is also the most difficult. The effects of improved driver behaviour are difficult to quantify and the psychology involved in improving the way the truck is handled can be quite complex. To get the best out of an operation requires professional truck drivers with a good attitude. This level of engagement with drivers can be difficult and fraught with problems.

Essentially, improved fuel use, and therefore lower carbon emissions, comes from a driving style which is more relaxed and more defensive than is normally the case. This improved driving style not only reduces fuel consumption but also wear and tear on the driveline and accident risk for the vehicle. Advocates of training reckon it is normally possible to maintain trip times even though a less aggressive driving style is employed.

A study involving Monash University and the Cement Industry Federation has demonstrated it is possible to achieve reductions in fuel consumption as high as 27 percent with the right driving technique and the right attitude.

The Strategix Training Group was invited to become involved in the study working with drivers from Blue Circle Southern Cement at Somerton in Victoria. The trucks were 68 tonne B-double bulk tankers hauling cement around a 30km test route.

After driving the course in their normal driving style, the drivers were then subjected to a training course aiming to improve the smoothness of their driving style and asked to drive the route again. Improvements in fuel consumption averaged out at 27 percent and when the test team returned 12 weeks later the drivers had maintained that fuel saving and had improved their normal driving style over the long term.

Basic tools of the kind of training required to improve fuel consumption are relatively simple. If there is an overall principle it is to derive the vehicle as smoothly as possible while still retaining road speed. Wayne Striplin from Strategix describes it as ‘flowing your vehicle’ and talks about ‘utilising the system of vehicle control, scanning ahead and preparing your vehicle to move through intersections and corners smoothly’.

One of the principal elements in keeping fuel use down is in keeping the rpm levels down. The higher the revs, the more fuel is being burned and over revving when changing gear can prove to be extremely wasteful. The principles of ‘progressive shifting’ have been well known for many years but very rarely practiced by the majority of truck drivers.

“When I was involved in driver training, I found the general knowledge among drivers about improving fuel economy was pretty poor, to be honest,” says Pat Cook from Western Star/MAN, who has a long history in the training industry with both Western Star and Queensland Transport. “I think, when you look back over time, we used to have the old engines like the GM which they told you to drive like your mother-in-law – like you hated it. However, when they changed it all around and brought in these high torque low revs engines people didn’t really adjust their driving.

“That is where the real bad fuel usage came from, these people have been trained to keep revving all the time. Engines changed but drivers never got any real training on how to use them. I was out there for Western Star and MAN working with the drivers but not every operator got that kind of training.”

On an industry standard Roadranger gearbox, drivers are trained to take each full gear as they work their way up through the gearbox, making the change at quite low rpm levels. The kind of recommendations made are to go to 1100 rpm in first, 1200 rpm in second, 1300 rpm in third gear and 1400 in fourth. When the driver reaches the high range of the gearbox, the progression rises from 1500 to 1800 over the next four gears to use the higher horsepower levels available to gain momentum.

“Down the bottom you are using torque and then in the high range of the box you are using horsepower,” says Pat. “Another crucial thing is reading the traffic. By coming off the power early and reading what’s in front of them is vital. Racing up to the back of a car and putting heaps of brakes on then having to go back to first gear again costs fuel. By going easier on the accelerator they keep the truck moving and keep their momentum up.

“The least number of gear changes will improve fuel economy. Every time you change gear, you are using fuel. When you look at downshifting on a Roadranger you have to tap the accelerator and the only way to increase rpm is to put fuel in there.”

Automated manual gearboxes have been used as a way of reducing excessive fuel use by the least careful drivers in a fleet. AMTs try and make gearchanges to minimise rpm levels even for those drivers with an extremely heavy right foot. The automated gearbox can also be a useful tool for the well-trained driver who can use an AMT to get similar results to the best-trained manual gearbox driver.

It’s all about influencing shift patterns by the driver. It is important for the driver to set off using a very light throttle to get the kind of progressive shift pattern manual drivers are taught to use. As the truck goes up through the gearbox the driver gradually increases pressure on the accelerator so that by the time the truck has reached the higher gears, changes are being made at the higher end of the green band to use the engine’s power to get up to highway speed.

It is still possible for a well-trained driver to get excellent fuel use results with an AMT if they use their knowledge to create a smooth flowing driving style giving the AMT the right cues to make gear changes at the right point. As the automated system cannot see the road conditions it will often err on the side of caution and hold on to particular gears longer than is absolutely necessary. In this case the driver can intervene by manually up shifting or feathering the throttle to induce an up change.

Using an AMT, it is probably easier to get less skilled drivers up to a higher standard than it can be using a manual gearbox. There is no need to develop those well honed Roadranger skills of matching road speed and rpm, they simply have to develop the subtle skills of influencing the automated system when it is required.

The driver can act as the eyes and ears of the AMT. The system itself exists only in a single moment and sets gear selection just using current parameters. The driver can see what is ahead and make a more informed decision about which gear the truck should be in. If the truck is about to descend a grade, a higher gear may be more appropriate. If it is about to climb quite steeply, a lower gear will allow rpm levels to rise, the turbo to kick in and the driveline can tap into whatever torque or horsepower it requires.

One of the advantages of using an auto gearbox is the baseline it creates in terms of fuel consumption. If a driver who has been fully trained to make his vehicle flow and get the best out of it in terms of fuel consumption regresses to their former bad habits, fuel consumption will still be better than a badly driven manual truck.

“If you had a fleet of 15 drivers, five will be very good, five will be very bad and five will be average,” says Pat. “You will get a worse result with those drivers running with a manual gearbox than you would with trucks fitted with auto gearboxes. But it is possible to get better results using an automated gearbox and the techniques we talk about with those using manual gearboxes. If you have a group of drivers who will sit down with you and they’re willing to learn, you can get good results for all of them.”

It is important to remember the driver influence on fuel consumption virtually disappears once the truck has reached 100km/h in top gear. The factors that influence fuel consumption in this situation are those discussed in earlier articles in this series: aerodynamics, tyres etc. The driver influence on fuel consumption is in the period from the truck being stationary until it reaches top speed and after it begins decelerating back down. Urban stop/go type fuel consumption can be heavily influenced by driver behaviour, long distance highway driving in relatively flat country, less so.

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