With apologies to the philosopher George Santayana, I’ll make the point that the BMW Head Up Display technology is in fact not the unalloyed blessing premised by BMW in their marketing material.
The downside, which the BMW engineers seem to have overlooked or not understood, is that HUDs are notorious for an effect called cognitive tunnelling. That is where a person involuntarily, and undesirably, fixes their mental resources on an information source, for some length of time, at the expense of monitoring other critical elements of the environment.
You are driving at 100 km/h on the motorway and glance at the speedo. Just one brief moment – yet you’ve just missed 28 metres of your route. That’s 28 metres in which a lot can happen. Unless, that is, you could pay attention to everything at the same time: such as with the BMW Head-Up Display….All the information individually selected by the driver with the BMW Head-Up Display activated appears there exclusively and no longer on the instrument panel. All in full colour and in brilliant resolution.
BMW online marketing material – retrieved 29 April 2013
Unfortunately, for the BMW engineers, putting information in the field of view leads to attention being focused on a much smaller Usable Field of View (UFoV), approximately 1 to 2% of the overall FoV. This leads in turn to the cognitive tunneling effect mentioned above. Nor is this a ‘theoretical’ effect, as studies of real world driving tasks have demonstrated (Lee and Triggs 1976; in Bossi, Ward, Parkes and Howarth 1997).
From a safety perspective this means that when HUD data is presented in the field of view there’s much less spare driver processing capacity left over to monitor the environment for high criticality low probability events. Such as, for example, a pedestrian stepping out into the street from between a pair of parked cars.
While certain performance advantages may be expected, drivers’ responses to some safety-critical events may be slowed significantly.
NHTSA Interim Report HS 808 320, 1997
Nor can we assume (unlike the aviation industry) a degree of homogeneity in the user population. The driving population covers a wide range of ages, and unfortunately we also know that the older one gets the poorer one’s UFOV becomes, which in turn ensures much greater cognitive channelling. This is one of the major reasons why there’s a higher rate of intersection accidents amongst older drivers (Ball and Owsley 1991). Now what was the demographic for BMW owners again?
Research has also consistently found that attention narrows under conditions of high arousal (e.g., high workload and/or stressful environments). So when driving at night, in bad weather or in an unfamiliar city a drivers ability to monitor for external events is going to be at an all time low, probably not a scenario where you’d like to further channel already limited attention into HUD data. Of course this is something of a problem for the HUD designers because what they’re trying to achieve is to ease the driving task, under these conditions…
Add to this the ability of the user to add information to the display, e.g ad hoc re-engineering of the interface, and the use of colour coding which can have unforeseen interactions with a dynamic background and you have, in my opinion at least, a complex error trap for drivers. And we’re going to throw this challenge at the older driver cohort who also have the recognised poorest performance in this regard?
As to how BMW were able to do what they did? I’d compare the relative immaturity of the automotive industry, in it’s regulation on system safety and human factors, to that of commercial aviation where there exists in contrast a strong national regulator with a culture of addressing the human machine interface issues of emerging technologies, all within a formal system safety management framework.
No BMW, as it turns out you can’t pay attention to everything at the same time, and designing an interface on that basis is asking for trouble.
Postscript – 2 Sept 2103
I’ve added an additional reference to a 2013 study by Cheng et al on HUD design. They found that the optimal display for driver speed stability was actually a low transparency HUD with an outline speed limit and a white and round speedometer.But they also found that the optimal combination for response time is high background transparency, outline speed limit symbol, green and a level (flat line style analog gauge) speedometer. found the users had bad performance to operation the speed and had longer response time for solid road speed limit symbol, orange and round & digital speedometer on HUD.
Ball, K. and Owsley, C. (1993). The useful field of view test: A new technique for evaluating age-related declines in visual function. Journal of the American Optometric Association, 64 (1).
Bossi, L. L., Ward, N. J., Parkes, A.M., and Howarth, P. A. (1997). The effect of vision enhancement systems on driver peripheral visual performance. In Y.I Noy (Ed.). Ergonomics and Safety on Intelligent Driver Interfaces. (pp. 239-260). Mahwah, NJ: Lawrence Erlbaum.
Cheng-Hung , H.,Chun-Wen, C., Tienwei, T., Ming-Hui, H. The Effects of Interface Design for Head-Up Display on Driver Behaviour. Life Science Journal 2013; 10(2): 2058-2065, 2013.
The Scientex Corporation – Human Factors Division, (1997) Human Factors Aspects of Using Head UP Display in Automobiles: A Review of the Literature, DOT NHTSA Report DOT HS 808 320, NTIS, 1997.