Fuel efficiency can also be enhanced by reducing the tare weight of the vehicle. This is also called light weighting. Greszler (2009: 111) notes that the benefits of weight reduction are more significant in weight-limited operations where less vehicle weight translates directly into increased freight weight, and improved freight movement efficiency. For volume limited trucks, vehicle weight impacts energy input due to rolling resistance, acceleration and hill climbing. Use of lighter materials, such as aluminium or carbon fibre, and fittings can substantially cut the tare weight. For example, the US Department of Energy and the American Trucking Association have a programme that aims to reduce the combined tare weight of the tractor and trailer in a Class 8 articulated truck by 2.3
tonnes. This may require a reversal of recent trends towards higher cab specification and the installation of larger fuel tanks, both of which carry a weight penalty. On vehicles meeting higher emissions standards by SCR, the installation of an additional tank for AdBlue further increases vehicle weight. Existing trucks already have widely varying tare weights. One study in Germany found that, across a sample of road haulage operations, the average tare weight of a 40-tonne gross weight vehicle was 14 tonnes while the minimum weight was 11 tonnes (Leonardi and Baumgartner, 2004). One major truck manufacturer has indicated that it is relatively easy to remove just over half a tonne from the tare weight of an articulated truck without adversely affecting its performance or carrying capacity.
Improvements to the fuel performance of new trucks is only one source of fuel savings, however. Companies vehicle purchasing decisions determine the rate at which new fuel-efficient technologies and designs are applied in practice. The way in which they subsequently operate and maintain the vehicles over a typical 1015 year lifespan also has a major influence on total fuel consumption.
Vehicle purchase decision
For technical improvements in fuel efficiency to be widely diffused and truck manufacturers to be incentivized to make them, operators will have to attach greater importance to fuel efficiency in their vehicle purchasing decisions. Research in Finland has found variations of 515 per cent in the fuel efficiency of different brands of new truck (Nylund and Erkkila, 2007). Comparing the results of the vehicle tests reported in UK trade publications reveals that 10 per cent variations in fuel consumption over a standard trial route are not uncommon for a particular class of vehicle. This suggests that a hauliers choice of vehicle can have a large impact on fuel consumption. Hauliers would be ill-advised, however, to base their purchase decision solely on fuel efficiency. They should analyse the fulllife cost of each vehicle and likely residual value before making their choice. Fuel expenditure should be a major component in this calculation. Market conditions can, nevertheless, work against the objectives of improved fuel efficiency where over-specified vehicles (eg with sleeper cabs for day-time operation) are purchased because they retain a higher residual value.
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Some companies purchase tractor units that are more powerful than they strictly require for a particular type of distribution operation. This is sometimes attributed to machismo on the part of the transport manager or owner-driver. A more rational explanation is that lorries with more powerful engines tend to retain higher residual values. This longer-term financial benefit, however, must be set against the additional fuel costs incurred in the interim. Because higher-powered vehicles are more highly geared, they tend to suffer greater loss of fuel efficiency at slower speeds. As road networks are getting more congested and average road speeds diminishing, the fuel penalty associated with over-powering is gradually increasing.
Vehicle maintenance
There is a huge range of technical imperfections that can prevent a lorry from operating at optimum fuel efficiency (DfT, 2006a). Many of them go unnoticed for weeks, months or years, wasting substantial amounts of fuel quite unnecessarily. Regular maintenance can help to detect and correct these defects. On a day-to-day basis, however, drivers need to be encouraged to look out for obvious signs that a vehicles fuel efficiency is being impaired. Typical defects include:
Ø Fuel leaks: a survey reported by the Freight Transport Association (1993) found that leaks in either the fuel supply or injection systems accounted for 44 per cent of fuel-related lorry defects uncovered during maintenance.
Ø Under-inflated tyres: according to a UK government report (DfT, 2006a), 20 per cent under-inflation of tyres will result in a 10 per cent increase in rolling resistance and cause a 2 per cent reduction in fuel efficiency. Michelin estimate that 58 per cent of tyres in the UK are at least 10 per cent under-inflated and thus incur a fuel penalty of 1.5 per cent or more (Buckley, 2006).
Ø Mis-alignment of axles: it is estimated that a 1º misalignment of a single axle on a multi-axle trailer will raise fuel consumption by roughly 3 per cent, while a 2º misalignment will increase it by 8 per cent (Buckley, 2006).
Ø Poor combustion: the emission of black smoke from the exhaust generally indicates that the fuel is not being properly combusted and energy is being wasted.
The choice of oil for the engine and gear-box can also have a significant impact on fuel efficiency. Impressive claims have been made in recent years for the new generation of synthetic lubricants that boast lower viscosity... and create less drag than do conventional mineral oils. Depending on the state of the vehicle they can yield up to 4 per cent savings in fuel (Anon, 2006).
Major advances have been made in the electronic monitoring of vehicle condition and performance, facilitating the detection of the range of technical shortcomings that depress overall fuel efficiency. Fuel efficiency is being given greater priority in truck maintenance programmes, partly because high fuel prices ensure a healthy payback for such measures, but also because of tightening controls on exhaust emissions.
