complicated and confusing interfaces lead to increased costs and reduced productivity. how can you design industrial vehicles that are easy to learn to use?

Most readers of iVT have probably, at one time or another, climbed

into the cab of a new or unfamiliar off-highway vehicle and suffered the

embarrassment – perhaps even in front of their colleagues – of

not being able to get a machine started and moving, let alone

operate it. Maybe it was a new high-tech

agricultural tractor with a CVT transmission and

electronics to rival a spaceship? Or even a complicated road

grading machine with dozens of seemingly conventional – but

actually unorthodox – controls? Either way, the plight of the

neophyte user is often the first symptom of an interface that is difficult to learn how to use. The ultimate cost of such a circumstance is very real, because a machine that is difficult to master will not be worked at its full potential until the operator can get up to speed and learn all the ins and outs of the vehicle. This learning period is best described by the learning curve: two machines that perform the same functions – but with different operator interfaces – can have tremendously different learning curves.

Although there is no denying that the considerable capabilities of many new vehicles might require a certain level of understanding and mastery on the part of the user, having to pull an inch-thick instruction manual out of its storage box to figure out how to get the machine to perform the most basic functions frustrates operators and wastes valuable time.

Needlessly complicated and confusing interfaces often reflect the decisions of an engineer who has failed to adequately consider the end users and their expectations, capabilities and limitations. A tricky and non-intuitive interface requires an operator with a higher level of experience and skill – and such an operator can be more expensive to employ on an hourly basis. Machines that can be operated by a larger portion of the potential workforce, rather than a few highly experienced individuals, will be less expensive to operate over the long haul.

This situation begs the question: what can be done during the development of an industrial vehicle’s cab and user interface to help make it easy to learn to use? There are a number of clear answers to this concern, and developing machines that are as easy to operate as possible is certainly in the manufacturer’s best interest. In fact, having an interface that is easy to learn and use should be one of the top objectives at the start of any vehicle development programme.

The learning curve Specialists in human performance often describe the changes in operator skill over time with a learning curve. Figure 1 presents two theoretical learning curves that might be seen on competitive machines with different user interfaces. A typical learning curve shows a gradual improvement in skill over time, followed by a plateau or levelling out after weeks, months or even years of practice by the operator. Although it was previously believed that operator

learning curve

sTeven casey

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performance flattened out entirely once the asymptotic level of skill was achieved, it is now known that the highly skilled operator continues to become more and more proficient, although the increments become smaller and smaller with time and increasingly difficult to measure.

Now it’s official: you can teach an old dog new tricks.

The measure of ‘operator/vehicle performance’ in our theoretical learning curve would depend on the type of industrial vehicle involved, but would be some combination of measures of both speed and accuracy of performance or the amount of work that is completed over a shift.

With Vehicle A, our operator continuously improves his or her level of performance over the first months of operation, and achieves a highly proficient skill level after about a year of work. Progress and skill development is consistent and smooth.

In contrast, Vehicle B is clearly more difficult to learn – or perhaps just more difficult to operate. Skill acquisition is irregular and less consistent, as the operator continually encounters barriers to achieving high levels of machine output. Performance also improves far more gradually, and it is only after a year-and-a-half of practice in our hypothetical example that the operator achieves a level of performance that might be considered ‘expert’.

So if our two vehicles have different user interfaces but are otherwise equal in all respects (such as horsepower, lift capacity, traction, etc.), it is reasonable to conclude that the performance differences are due to the design of the user interface.

Positive transfer and operator expectancyOur first technique for maximising the ease of use and learnability of a machine’s user interface is the principle of positive transfer. An interface should capitalise on the skills that an operator already possesses, not force him to work against those skills or unlearn them.

Most industrial vehicle operators come to the stage with a great deal of experience in operating a car, for example. Why not take advantage of this and have the controls on an

industrial vehicle work in much the same manner as they do on a common automobile, relying on the principle of positive transfer?

Most industrial vehicles operate within a fleet of other vehicles. When user interfaces in different vehicles operate similarly, operators can move from one vehicle to another and experience the benefits of positive transfer. Negative transfer occurs when an operator’s previous experience and expectations make it more difficult to operate a new machine. This effect is

figure 1: Theoretical learning curves for two machines with different user interfacesThe hinge on a door is an ‘affordance’ that ‘tells’ the user how the door operates

Standardised colour codes help operators move from one machine to another

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often found on joystick controls where manufacturers use dissimilar or even opposite control mapping for joystick functions. Interfaces that create conditions of negative transfer are invariably more error prone and most certainly will take longer to learn and operate consistently.

‘Expectancy’ is the term for describing what it is that an operator might expect upon first exposure to a machine’s controls and displays. Most car drivers in the USA and mainland Europe, for example, expect to find the headlight switch to the left side of the steering wheel, either on the console or on a stalk.

Locating the headlight switch where it is generally not expected, such as to the right of the steering wheel, increases the reaction time necessary to find and operate the switch for most drivers and also increases the probability of the operator making an error.

‘Oh,’ you might argue, ‘but the operator will get used to it being somewhere else.’ There is a grain of truth in that argument, but operator performance will be faster and more

reliable when controls operate as users expect them to, and expectancies are most heavily influenced by the totality of experience rather than exposure to a single vehicle interface.

In summary, know the expectancies of your target user population and reflect them in the layout and operation of all controls and displays. Designs that conflict with expectancies will be more difficult to learn and use.

Product affordances An ‘affordance’ is an inherent connection that a user might make between a characteristic of a product and its use; something that tells the user, in a natural or innate way, something about the product.

A visible set of hinges on the outside of a door, for example, tells the user that the door opens towards them – in the direction of the hinge. The hinge in the door serves as an affordance. Hence the affordance is a valuable cue to the operator and helps shape appropriate behaviour. A door with a horizontal exit bar and no handle (and no visible hinges) suggests to the user that it can

only be pushed and not pulled. Similarly, a gate on a transmission shifter provides a strong cue about the possible directions of movement of a transmission lever and its possible stopping points.

Removing the visual cues provided by affordances increases operator uncertainty and reaction time. Many modern industrial vehicle interfaces dispense with traditional affordances that would otherwise provide valuable cues for the user. Although they can be designed to be quite effective, many touch-pad and touch-screen interfaces, for example, dispense with the natural information that a traditional interface might have provided to the user.

It is vitally important to understand these subtle sources of information for the operator and find ways to replace them when newer interface technologies are employed.

Hidden and unknown features When I consulted with an automobile manufacturer about a new vehicle a few years ago, the product manager informed me that he wanted to have hidden features in the vehicle that the user would only discover, preferably by accident, some years after the purchase of the car.

Each time the user discovered one of these features, the product manager reasoned, he would experience a certain sense of ‘delight’ and renewed satisfaction with his purchase. I argued that such an approach was wasteful and foolish. If a vehicle has a particular capability – such as an intermittent windscreen wiper or a timing delay for turning off the headlights – it should be obvious to the driver in all respects. If not, the driver is not really getting what he or she paid for.

Obvious or not, it is surprising how many users are unaware of the capabilities and features of the vehicles they operate. It may be that the features are truly hidden from sight or that the operator has never had the time to read through the hefty instruction manual. Either way, such a circumstance is often an indication that the interface itself does a poor job conveying the vehicle’s features and capabilities to the operator.

Another type of ‘hidden’ feature – the unintentionally hidden feature – is surprisingly common in modern electronic interfaces. Again, the control should suggest the action that can be taken with it. Many touch-panel or membrane switch applications do not fully convey how they are to be operated. Some require special inputs on

Top lefT: A visible gate tells the user the possible positions of the controlTop righT: ‘Smart’ displays can be used to tell the user the functions that are available at a particular point in time. above: Yellow is used to identify controls for moving potentially hazardous machine elements

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the part of the user, rather than simply pressing a button. How is a user supposed to know, for example, that a membrane button has not only to be pressed, but pressed and held down for three seconds for it to be activated? Such situations create the need for additional training, instruction, fiddling with the controls to try and figure out how they work, or pulling out the thick operating manual once again.

One of the more dreaded circumstances for a new operator of a vehicle is encountering an impasse or dead end; a point at which he or she simply cannot determine how to move on to the next stage of operation. Many situations such as this are attributable to hidden features or control functions that are unfamiliar to the user or not especially obvious.

grouping, labelling and coding Logical and functional grouping of controls, in addition to placing controls where operators expect them to be, also

contributes to the ease with which a new user can learn to operate a vehicle.

The ASAE (American Society of Agricultural Engineers) recommended practice for control colour coding in agricultural vehicles contributes to the ease of use and understanding of controls in simple utility tractors right up to big and complex combines. Controls used to switch on or shut down the machine are red. Controls used to regulate speed, including the throttle and transmission, are orange. Controls for starting and stopping important and potentially hazardous moving parts such as PTOs and augers are coloured yellow.

Application of this design practice helps operators to move not only from one type of machine to another, but also from one manufacturer’s machine to a machine by another maker.

Consistency in other aspects of control design is also important. Control handles can be shape coded so that their function can be sensed with the hand alone, while controls that are located where

operators expect them to be located will be operated more quickly and reliably.

Pretesting with actual users Perhaps the most effective technique for identifying usability issues with vehicle interfaces is to conduct objective tests with the actual users. Tests can be conducted with actual or prototype equipment, but also with simple mock-ups or simulations. What is vital is that the tests are conducted objectively with the goal of measuring the ease with which users learn to operate the machine.

Again, the focus must be on actual product users who have not been biased during the development process. Well-executed pretests with actual users will also identify which aspects of an interface are easily grasped – thereby allowing engineers to focus their efforts on improving the usability of elements that are not so well understood. iVT

Steven Casey is president of Ergonomic Systems Design Inc in Santa Barbara, California, USA

lefT: Push button control surfaces are differentiated from simple icon displays through colour highlights and grouping above: Familiar use of red-yellow-green colour coding on a display

lefT: Effective grouping of controls by function; Top CeNTre aND righT: Ground movement controls identified with the colour orangeabove CeNTre: Specialised control functions identified with secondary colours

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