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Weighty options

21st October 1993
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Page 44, 21st October 1993 — Weighty options
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Which of the following most accurately describes the problem?

Flip through Commercial Motor's legal pages on any week and the

chances are you'll find a court case on overloading. Some are clear-cut: An operator or driver has tried to profit from carrying more goods than is legal and he's paid the penalty. Quite right too. But keeping on the right side of the law isn't always easy. Even the most professional driver can make a mistake when loading a truck and this can have a serious impact, on not only your driving licence but also on the company 0-licence.

In the first of our new monthly Drivers' Guides we've set out to describe the mechanics using a dynamic axle weigher. We've also highlighted what happens if you're found to be overloaded.

Vehicle loading and weighing are often seen as black arts. Don't be fooled. The more you know about them the better your chances of getting it right.

• Every HGV operator and driver is familiar with the regulations governing vehicle use and weight, so they should be equally familiar with the Operator's Licence which every operator has to obtain. To get this licence it is necessary to complete Form GV79 which requires the operator to state his intention to ensure that his vehicles are not overloaded. Failing to do this can put his licence at risk.

During 1992/93 just over 1:500m was spent on road maintenance.Although this amount cannot be wholly attributed to too many overladen vehicles on the roads, it cannot be denied that with so much more traffic on the roads, a huge proportion of the sum must be due to repairing wear and tear. An 11-tonne axle increases road damage by about 125% more than a 10-tonne axle, and if we consider how many lorries there are on the roads over 11 tonnes, it is quite easy to see why so many roads always appear to be under repair.

From a business point of view, this will affect a haulier in two ways: road tax will increase to pay for all these repairs—and those repairs cause traffic jams which makes a driver's life harder. So it's in the your own interest to avoid overloading, but it doesn't only come down to self-interest. If your vehicle is stopped and found to be overloaded, these are the penalties you might have to face: • Overloading is an offence under the Road Traffic Act and carries a maximum penalty of £5,000, • Overloading convictions can affect the decision of a Licence Authority to suspend, revoke or renew a driver's HGV licence.

• Overloading convictions can be taken into account by the Licence Authorities who may decide to take action against the 0-licence holder.

When applying for an Operator's Licence, the authorities have to be satisfied that there are acceptable arrangements for avoiding overloading.

Unfortunately these days it is not enough to calculate the laden weight of a vehicle by adding the unladen weight of the vehicle to the weight of the cargo, as there is now so much emphasis on axle weights so other methods of accurately weighing vehicles are constantly being sought.


The weight of an object is defined as its volume multiplied by its specific gravity (SG). A way of illustrating specific gravity is to consider the difference between a tonne of, feathers and a tonne of lead. Both weigh the same, but have vastly different volumes. This is because the specific gravity of a feather is far less than that of lead.

The volume and specific gravity of an object such as a cube of wood is easy to calculate as it is a regular shape and is of the same material throughout. Unfortunately, a truck doesn't have a regular shape, nor is it made of a single substance, so it's impossible to work out its exact weight mathematically.

WEIGHING METHODS To weight a truck you've got to compare it with a known range of weights (eg grammes, kilogrammes and tonnes) with the use of some form of weighing machine. On a set of scales, weights are added to one side of the scale until they exactly equal the weight of the object on the other side. This is considered one of the most precise weighing methods, providing the weights used are accurate.

However, to weigh a truck a more substantial weighing machine is required, and there are several devices available for this. Some use the distention of a spring to move a pointer over a scale, others use strain gauges to give an electronic output, and yet others use the displacement of fluids to arrive at a result.

The only drawback with all these methods is that their results are relative, comparing the object being weighed with known weights using an indirect means--be it gauge, dial, scale or electronic readout. Therefore it's important to recognise that no weighbridge can ever be totally accurate all the time. A simple test is to take a vehicle to several trade weighbridges under similar conditions of load and fuel and compare the results!

On top of the problem of the actual accuracy of the weighing machine being used, there is also a problem when it comes to weighing something as large as a vehicle in the fact that it is not always possible nor desirable to weigh all the vehicle in one operation, as sometimes operators wish to weigh vehicles axle to axle. "Split" weighing, such as taking axle weights, is therefore the only solution. This causes further problems.

5t 5t 5t

The above-ground methods of split weighing a vehicle is where the risk of weight transfer-shift of the centre of gravity--is greatest, and in this instance a portable weighing machine will illustrate the major pitfalls of split weighing.

First it should be remembered that the closer the axles are to each other, the greater the chance of weight transfer and the greater the effects of this transfer of weight (see diagram, left).

This is further illustrated if we take a three. axle trailer bogie as another example. For the purposes of showing weight transfer, we will assume that the three axles are independently suspended and that the trailer chassis is rigid (see top diagram).

The only way to avoid this kind of weight transfer is to raise all the axles simultaneously to the same height above the ground (diagram overleaf).

The in ground method of split weighing is less likely to give weight transfer so long as the ground on either side of the weighing platform does not significantly rise or fall

Al under the remaining length of the vehicle. In this instance, an axle weighbridge will illustrate how weight transfer can occur on fixed systems.

Where the roadway maintains a constant gradient, (see diagram below) the weight transfer is zero or minimal. However weight transfer occurs where there are changes in gradient (illustrated right). To make matters worse, gradients are not the only consideration when thinking about axle weight. Load distribution is also important.

As shown in the illustration on page 43, both vehicles carry the same payload, both have a legal gross vehicle weight and yet one of them is illegal.

We have seen that unless we have a machine that can weigh the two vehicles in one go, there are several important aspects that have to be taken into consideration when split weighing a vehicle in order to achieve a accurate result and avoid prosecution.

There are many different types of weighing equipment in use within one of the following categories: 1 Full length weighbridge.

2 Part length weighbridge.

3 Axle weighbridge.

4 Portable wheel or axle weigher.

5 On board weighing system.

The major advantage of this type of machine is that it will give gross vehicle weight in one operation with no worries about weight transfer. In general it can also be expected to provide a high level of accuracy. However, it is an expensive way of obtaining axle weights especially if your business does not usually entail weighing your vehicles and is not a -practical means of doing so being quite time consuming-especially with multi-axles.

And when axle weights are being taken on this type of weighbridge the dangers of weight transfer are the same as for any other type of weigher.

This is essentially a compromise between a full length and an axle weighbridge. It costs less than a full length weighbridge and gives an easier method of obtaining axle weights, as most units will accept a tractor or trailer bogie in one operation.

However, it is a more expensive and less practical method than an axle weighbridge. Some vehicles with close-coupled axles use a suspension system that is dynamic or self compensating.

With this type of suspension the weight of the bogie is transmitted to both axles in such a way that the weight on any given axle can and usually does vary from moment to moment depending on the way the suspension adjusts itself, In practice this means that such bogies can never be accurately weighed by an axle weighbridge. The only satisfactory method is to weigh the bogie as one unit and then derive an 'average' axle weight. The partlength weighbridge is one such way of doing this.

Axle Weighbridge With the single exception of the axles mentioned above this type of weighbridge provides the easiest and quickest method of obtaining axle weights. It should also provide the most cost effective method. The major consideration when using these types of weighbridges is the suitability of the site to accept a weighbridge to give accurate axle weights. The risk of weight transfer during the weighing will be the determining factor in levels of accuracy, irrespective of the inherent levels of accuracy of the weighbridge or indeed how much you have paid for it.

Portable weigher This is probably the most versatile method of weighing as in theory it should be possible to weigh any wheeled vehicle, anywhere, anytime. However, the more axles a vehicle has, the more units needed to weigh it correctly and the more time it may take to do this. It is also easier to cause weight transfer with this type of equipment. For twin axle vehicles and for off-site/awayfrom-base weighing, or where the weighing demands are not particularly high it is probably the most cost-effective method.

Since these systems are on board, they can only register weights that are 'above' them . There is also a danger that this type of equipment will tell you what load is being carried but not how the load is distributed and hence its effect on axle weights. This category is possibly the least flexible method in that each vehicle in the fleet has to be fitted whereas any vehicle can use a single weighbridge. Another potential problem with such systems is how they are calibrated in the first place.

Most vehicles have a manufacturer's plate showing the maximum gross and axle weights for which the vehicle is designed. At the time of registration, vehicles are plated by the Department of Transport as well. This plate shows the legal gross and axle weights for the vehicle. If there is a difference between the two plates. then the DOT plate prevails. The maximum payload of the vehicle is the plated gross weight less the unladen weight of the vehicle—which is not plated—but which also includes fuel, tools, lubricating oil, spare wheel, water, spares and the driver.

Although it is safe to assume that each vehicle is correctly plated it is not safe to assume that every driver will be aware of axle limits. Each vehicle should have a card in the cab that gives these weights to remind the driver of his obligations and responsibilities under the law.

There are official codes of practices governing the correct use of weighbridges used for enforcement purposes, including dynamic axle weighers, plate bridges and the unique multi-axle weigher based at Ross-on-Wye. The weighbridge operators are required to be familiar with the relevant code of practice and to operate them in line with its recommendations.

Unfortunately not all enforcement officers are aware of the codes—or choose to apply them! This can be an extremely important defence argument when facing an overloading prosecution.

It should be possible to obtain a copy of the Dynamic Axle Weighing Code of Practice which is published by the Department of Transport. (Its original catalogue number is GV230),In its introduction the code states; "The object of the code is to provide operators, drivers and road traffic enforcement officers with information on the correct setting up and operational use of the dynamic axle weighing systems." Drivers and operators should get a copy—and read it.

Accidents happen and when they do, despite the pleas of mitigation,you could find yourself looking at a hefty fine for overloading. How hefty depends on where you are in the country as there's little consistency in how Magistrates' Courts set the level of fines for overload. ing.

The Magistrates Association has a broad tariff which is likely to be applied for overloading offences before any mitigating circumstances are taken into account. The basic formula is a set fine plus a percentage increase dependent on the degree of overloading. This effectively gives the Magistrate a sliding scale of fines.

As well a levying differing fines Magistrates frequently treat separate axles as separate offences; there are up to nine potential overloading offences on a 38-loaner including: train; gross; three axles and compensating axle.

A more worrying trend is where Magistrates listen to a strong defence only to still convict the driver or company and set a nominal fine.The defendent must then decide whether to accept the small fine or fight the conviction in an appeal which will mean incurring more legal costs.

Before appearing in court the driver and company should seek proper legal advice, preferably from a solicitor with experience in road transport. The company and driver have a legal obligation to notify their local Traffic Area office of any overloading conviction.

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