Stefano Pasini

On-board Automotive Instruments: Information or Distraction?

(Draft- 6-11-00) 

Since the beginning of its history, the automobile has needed instruments to monitor some of its many functions. From the engineer’s point of view, there was an obvious need to keep a strict control of the engine’s health through the number of revolutions per minute (rpm), the lubricating fluid pressure and, in the cars with water-cooled engines, the coolant temperature. Legal needs forced the introduction of a speedometer, whilst the lack of any visual indication of the quantity of fuel carried on board was rather surprising, considering the scarcity of refuelling stations available.

The instruments installed on the ‘dash’ of the cars of the Veteran/Vintage era were not more than an adaptation of the manometers, thermometers, etc, that had been already developed to monitor steam boilers, locomotives  and road engines. The first ‘visual interface’ between the driver and his automobile was primitive indeed, but then one must remember the dreary conditions of the road, the erratic behaviour of the cars on their balloon tyres and vague steering, and the general lack of road discipline amongst the other users, pedestrians, horses, carriages. The driver had plenty to watch while driving: the instruments were not his top priority.

Paradoxically, now that the engines are so much more advanced and the cars, as a whole, so reliable, we find ourselves in dire need to improve the efficiency of the instruments layout. However, our goal now is not only to obtain a better control of the engine’s vital data, but to improve on the man/machine interface, trying to offer to every driver a better driving environment. This because a pilot that is not unduly distracted by his car’s instruments will obviously enjoy a safer and less tiring driving performance, and at the same time he will still be able to find all the relevant information quickly and without losing time.

Unfortunately, one must observe that since the ‘70s and the sudden upcoming of cheap LCD displays, there has been a veritable multiplication of layouts whose final task seems more to impress the buyer than to help and assist the driver. As this, for the latter, could mean an added distraction and to more mental workload, it can lead to disaster. Therefore, this danger has to be prevented with a judicious approach to the instruments’ design.

DESIGN CONSIDERATIONS

While designing an instrument layout for an automobile, it is necessary to select the data that the driver has to be informed about. It is possible to classify these data in three classes:

a) the data that have to be permanently displayed,  

b) the ones that need  to be displayed only occasionally or ‘on demand’ and

c) those that will be displayed only in case of failure/danger.

Usually, most of today’s cars keep their user permanently informed about the condition of the engine (coolant temperature, lubricating pressure, rpm), whilst the other main permanent indication is the travelling speed of the vehicle, the latter  being also the only indication that, in the vast majority of Western countries, is mandatory by law. But buyers allegedly prefer a higher degree of complexity in their cars’ instrumentation, and it is therefore necessary to understand what the average driver really desires and why. An order of preference is, in this case, very useful, as one could ideally build a very rational instruments layout assembling the really necessary dials in a restricted, ‘visually-privileged’ area located in the most advantageous zone of the driver’s dynamic visual field. We can call this are, that is the part of the facia that is visible inside the steering wheel’s rim, the ‘core area’.

With this purpose, researchers from Delco/GM performed an interesting research (1) asking to the components of a large group of drivers what information they preferred to have continuously displayed in their car. The researchers found that the drivers wanted above all the indication of travelling speed (96% of the respondents), fuel level (88%) and time (84%). The rotational speed of the engine was deemed to be necessary only by 64% of the respondents, and it is therefore quite amazing to see that almost every car produced today has a rev counter as large as the speedometer, whilst the clock is all too frequently a small digital display of an unfortunate background hue, located out of the instrument main ‘binnacle’ and, more often than not, quite far from the driver’s eyeline. The conventional instruments layout, as favoured by the automobile designers of today, therefore penalise the clock, that more than 4 users in 5  perceived as ‘necessary’, and implant in its natural location instruments for indications generally felt to be even less indispensable by users, such as water temperature (50%).

It is clear that there is a marked discrepancy between what the engineers would like to monitor, the designers think fit to install in an instrument panel, what the marketing people believe that will help sell the car, and what the desires of the final users actually are. As the instruments are amongst the first things that the perspective buyer looks for and sees while examining an automobile, the marketing people usually win and, as a result, most of today’s cars’ dashboards are overloaded by multiple, often scarcely useful, dials, lights and displays. This abundance is used in the hope that layouts of such complexity will earn even to the more mundane of cars some of the flavour and added-value of their more expensive relatives, the cars where such complex layouts are usually adopted for good reasons: the aristocracy of the automobile world, sports- and luxury- cars.

This approach, from the ophthalmologist’s point of view, is not correct. Too many instruments, when not absolutely essential, impair the readability of the layout. The response time to locate information is strictly related (with an inverse ratio) to the display density. This table (2) show how density impairs readability.

It is evident that packing too many data in a limited space is not only useless, but it can be actually counterproductive. Instruments are not marketing gadgets: they are, above all, instruments, and they must be designed keeping in mind their one and ultimate goal, transmitting to the driver/user the data that are actually important for the driving task, avoiding all excesses. Unnecessary information clutter the instrument panel, lessens the visual importance of the really important ones and therefore lengthen the reading/understanding process, thus keeping the eyes of the driver off the road for a longer time than it would be desirable.

It is unfortunate to observe that fashion considerations, and the wish to imitate larger and faster cars, have led the designers to install such a dazzling array of unnecessary dials even in normal automobiles. Whilst the rev-counter is a necessity in a high-performance sports car, it is obviously little more than a decoration for a small family saloon, and even the coolant temperature gauge is pleonastic: it can be substituted with a simple warning light that would go off if the temperature goes over the limit.

The design of some instrument panels is, apparently, more dictated by marketing than by ergonomics. The idea behind this kind of design is that the buyer will be impressed by the intricacy of an instrument panel and will attribute to the car, thanks to this factor, a higher intrinsic value, thus he will accept to pay a marginally higher price for it. Larger dials, more warning lights, brighter displays will therefore earn the manufacturer more money, or so it is believed.

From the ergonomic point of view, this approach is not correct, at least not for the vast majority of mainstream saloons, Station Wagons, SUVs, MPVs and light pick-ups. The most important instrument, for dynamic and legal needs, is the speedometer: this has be given the most easily-read position in the instrument cluster, and dimensions to match its functional importance. The clock and the fuel level gauge could flank the speedometer for aesthetic purposes. The resulting layout would be functional and aesthetically pleasant; a careful design of the dials would raise their perceived value and improve the product desirability of the simplified panel.

ANALOGUE OR DIGITAL?

Instruments may communicate their data to the user in three styles.

a-      Analogue

b-     Digital

c-     Warning light

These three layouts are not fully interchangeable. Though specific arrangements could adapt either of them to display any kind of data, an analogue instrument will be more easily adapted to a ‘check reading’, a digital readout will be more apt for a ‘quantitative reading’ and the warning lights are perfect for ‘status reading’, like an on/off alternative. (2)

Though the great accuracy of the digital readout is obviously advantageous, and would make it a theoretically good choice for some instruments, in fact the ease of understanding of an analogue dial makes it extremely functional for the speedometer, the fuel level and the clock. This is due to the fact that an analogue instrument gives to its user a graphic signal that can be easily understood: the eye can easily acknowledge the angular deviation of a pointer, especially if it is designed so that it is vertical while indicating a  ‘normal’ value. Stereotypes for this kind of dial are such that the hand a clockWhise rotation of the hand indicates a ‘rising’ value, and so the designer would have to arrange the dials. Any design going against a stereotype will impair the users’ performance, even after a thorough training, especially in an emergency situation.

The digital readout would preferable, in a motor car, for several minor indicators. The odometer, outside temperature display and possibly the requested HVAC temperature/operating mode could be successfully displayed through compact LCD screens housed in the lower part of the speedometer dial.

The warning lights could advantageously take care of any other indication, as the driver really needs to be informed of the other functions of his car only when something goes wrong. The blinking of a red or orange light in the middle of the instrument binnacle would have a powerful warning effect without the waste of space

COLOURS: KEYS TO PERCEPTION

We ‘see’ the things that surround us thanks to contrast. Without contrast, as a gradient of luminance between two bodies, we wouldn’t see anything, as it happens in dense fog. Enhancing the luminance contrast between two figures betters in a significant way the readability of the indication they carry.

This mean that a high-contrast visual indicator will be seen and understood much more easily and in a shorter time than a similarly-sized instrument with a lower-contrast design. To achieve this goal, the more classical design remains a black dial with white numbers and hands. It has many advantages, and the main one is precisely the fact that this design offers the maximum contrast possible. If the instrument is round, the eye will not ‘escape’ out of it as easily as it would with a square dial.

White-on-black lettering will therefore be the best choice, but using a bright orange ‘hand’ will not harm its visibility in normal daylight. It is, however, scarcely advisable to use the oragne or red colour for a pointer if it has been decided to use a green/blue instrument illumination; the reduction of brightness (luminance) of a red/orange pointer when lit by a green lamp will unavoidably impair its readability exactly when it ought to be at the maximum level, during night driving.

POSITION

It is widely ackowledged that it is advisable to  ‘locate information of a critical nature near the center of the screen’.(2) In the design of a new instrument panel, the most important dial, the tachometer, will therefore keep a commanding position in the central part of the panel. This is due to the necessity of keeping the eyes of the driver as much in line with their most important target (the road) as possible, not forcing them to deflect too much nor vertically nor, and this is perhaps more important, horizontally. Ergonomicists think that ‘the most comfortable angle for the eye is about 15° downward and straight ahead’ (2) whilst the horizontal deviation would not have to be more of 15° from the centerline, on either side. A direct consequence of this is that the idea position for the instrument panel still is the ‘classic’ one, behind the steering wheel, and that it has not to be too low. Whilst the HUD (‘Heads-Up Display’) at the basis of the windscreen, though conceptually attractive, is believed to be too invasive and a possible (probable) source of distraction; what is good for the young, highly-skilled pilot of a Mach 3 fighter airplane flying in the three-dimensional unlimited space of the open sky is not necessarily as good for the average driver crawling in dense traffic on a strictly bidimensional and much crowded street.

TO NOBILITATE A SIMPLE DESIGN

An implicit commercial danger of the proposed simplification of the design of the instruments is that the average user, instead of understanding the functional advantages that this ergonomically-advanced layout would bring him, would judge it ‘too simple’, i.e. ‘too cheap’, for his new car. This is what usually prompt marketing experts to claim for a more intricate, gimmick-laden instrument complex. A more reasonable approach would be to stick to the simpler layout, taking care to explain to the perspective buyer that a simpler panel is not necessarily adopted to save money, thus that he doesn’t have to feel deprived if his car has fewer instruments.

To take care of this feeling, the technical basis of this instrument panel will have to be quite sophisticated, substituting quantity (many dials of average quality and design) with quality (fewer dials, but with a distinct high-tech flavour).

The technological basis for a truly advanced, technically effective and commercially advantageous instrument panel already exists. The designer can choose optotronic instruments, TFT displays and other devices to recreate, on the instrument panel of a new car, the best layout with a cost comparable to the traditional analogue or digital layouts but with the added advantage of a remarkable compactness, an attractive, state-of-the-art set of instruments that could be at the same time cost-effective, space-saving and customer-friendly. ‘Reconfigurable’ instrument panels will undoutedly offer an interesting perspective for the future, offering the possibility to tailor each and every panel on the single customer’s preferences.

One must anyway remember that legal requirements will always force the designer to maintain a speeodmeter at the centre of the instrument panel, that a fuel level gauge will have to appear routinely, at regular intervals, to remind the driver of his supply before the low-fuel warning light turns on; and that a clock has to be continuously displayed. This said, there is possibly nothing against showing on a discrete TFT screen a wealth of data regarding oil pressure, radio station name, etc., provided that this kind of display doesn’t substract space to the main dials.