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Taking the human error out of driving

Head-up displays and station keeping indicators are among several devices being tried out at TR R L in an effort to reduce the need for driver responsibility IN the current Experimental Safety Vehicle (ESV) programme there should be more emphasis on avoiding accidents — as well as improving vehicle safety.

This assertion was made by Mr H. A. J. Prentice MSc, BSc, CEng, FlinstP, AFR AeS, head of the road user dynamics division of the Transport and Road Research Laboratory, when he was presenting his paper "Accident avoidance: drivers' limitations" at the fifth international technical conference on experimental safety vehicles in London last week.

Although the conference, which included the presentation of more than 90 papers, sponsored by the US Department of Transportation, was almost exclusively concerned with the progress of safety car design Mr Prentice's paper dealt with topics equally relevant to commercial vehicle design and operation.

Mr Prentice said that accident studies had concluded the primary causative factor to be driver misjudgment. It was, however, very difficult to arrive at the precise extent to which any particular aspect of driver performance was responsible for a particular accident.

Judgments of speed and distance, said Mr Prentice, were fundamental to achieving correct decisions. The experimental studies which had been conducted in this field of work had shown that road users lacked the inbuilt ability to make the more critical of these decisions with the precision required.

Overtaking experiments

Overtaking experiments suggested that if very fast or very slow moving vehicles were involved it was not until quite late on in the manoeuvre that the message from the visual perceptual system was sufficiently strong to overcome the driver's expectancy.

This suggested that aids in or on the vehicle or on the roadway to assist in the judgments of speed and distance would have a considerable potential to reduce accidents. Already fast-moving public service vehicles, eg police vehicles, ambulances and fire engines were indicated as such by means of flashing lights.

The need was to develop driving aids which supplemented out the deficiencies or if necessary even took away the freedom of choice of the individual to carry out certain manoeuvres. The decisions as to which equipment could be made available depended to a large extent on the cost of the device or system as against its success in accident reduction.

The following sections gave details of some devices currently under investigation in the UK, both for use on vehicles and in the environment, and made some suggestions as to areas in which research might be undertaken to give profitable results.

One approach to the problem of safe following of vehicles at high speeds and short headways was to use radar or a related system. These techniques were being investigated in many countries besides the UK. In the first instance it was likely that such a headway measuring system would be used as an aid to drivers, to warn of too close following or of brake application by a vehicle ahead, and perhaps to tighten seat belts before a collision. After adequate operational experience the system could be extended to automatic control of throttle and brakes.

The ideal headway measuring system should be: (a) self-contained, ie not requiring "co-operation" from the vehicle ahead or the road, (b) able to operate in all weathers, (c) able to detect and respond quickly to sudden brake application by the vehicle ahead, (d) fail-safe, (e) able to detect road obstacles as well as vehicles, (f) cheap and reliable with few false alarms, (g) able to handle lane changing and merging as well as simple following.

No system known at present could meet all these requirements, but an obvious starting point was a forwardfacing primary radar. This had many attractions, being self-contained, potentially cheap and easily introduced. However, the great accuracy of range of relative velocity measurement needed for quick detection of brake application by a vehicle ahead was very difficult to achieve under real road conditions, cluttered as these were with roadside furniture and multiple vehicle targets.

A high frequency (eg 30GHz) was needed to give a narrow enough beam from an acceptably small antenna, and this increased the difficulties of making a radar work reliably in the road vehicle environment which presented a most demanding combination of vibration, temperature changes, electrical noise. and exposure to the elements.

Trials carried out at TRRL with lOGHz Frequency Modulated Continuous Wave (FMCW) sets had not been very successful as they failed tc measure ranges accurately on the road. A 34GHz FMCW set using flat printed aerials was being developed, but there were some problems of reliability which remained to be investigated.

Research into ways of overcominE these difficulties included studies of (a: radars using passive frequency-changini transponders on the target vehicles; (13: an active co-operative telemetry system.

A passive transponder system using t frequency doubler had been demon. strated by Radio Corporation 01 America. It offered the great advantage! of virtually 100 per cent clutter rejec. tion and alleviation of the primar3 radar's difficulties when following, foi example, the case of a very small car which was following a very much larger vehicle.

A telemetry system had potential benefits which might justify its extra complexities. Its principle was that each vehicle measured its own position with respect to the road and transmitted this to all nearby vehicles. Each vehicle now knew where all other vehicles in the vicinity were and from this could derive a speed command voltage to control throttle and brakes to maintain its correct position. The advantages of this approach were that it could be used to deal with merging, crossing, and lane changing, which were beyond the capabilities of other systems. It should also allow following at very short headways without requiring very accurate range and relative velocity measurements.

Head-up speedometer It was generally accepted that speed in excess of that suitable for the prevailing situation was one of the primary causes of accidents.

Experiments had shown that drivers used their speedometers infrequently. It had also been found that drivers relied upon sensory information instead of their speedometer during manoeuvres, or in traffic when making speed adjustment. In addition drivers were unable to make accurate visual estimates of their speed. A further factor was the time which was taken to read an ordinary speedometer. Experiments had shown that the average time required was 1.6sec and this was probably the reason why in heavy traffic or during difficult manoeuvres the drivers did not look at their speedometers.

If, therefore, it were possible to present vehicle speed to the driver without requiring him to look away from the view ahead then this information could he used much more readily. The informItion could then be obtained by a momentary change of view instead of requiring the driver to take his whole mention away from the road.

Prototype Head-Up Display (HUD) mits had now been manufactured and a -lumber of them had been undergoing xtensive road trials (CM May 10). The principle of operation of such an EIUD system was relatively simple. Light from a rotating disc or electronic iequence of numbers was projected ipwards on to the windscreen through a ens system so that after reflection into he driver's eyes the images appeared at i distance ahead of him. The image yrightness might either be controlled iutomatically using photocells or nanually by the driver according to his )reference.

One problem that had become ipparent during the trials was that the naximum brightness available was insufficient for viewing against snow, low sun, etc. The other problem which had arisen was that of height adjustment for individual drivers. The setting of the light reflected from the windscreen was chosen in accordance with the standard eye position ellipse currently used in vehicle design. This apparently was not satisfactory and the range of positions would need to be extended.

The question frequently raised was whether the speed information received in this manner was a distraction. Experience with this equipment showed that after a few days the novelty wore off and the information was taken in virtually unconsciously. An interesting point was that the driver was immediately aware of losing his speed display. This could occur when driving into the setting sun when he would of course experience great difficulty in reading a conventional instrument.

If HUD systems were adopted for use in large numbers of vehicles other advantages would follow. For example, it would no longer be necessary to have all instruments like oil pressure gauge, water level, engine temperature, etc, high up on the dashboard of the vehicle. As readings varied from pre-set limits a warning light would be projected through the display to alert the driver to consult his instruments.

Station-keeping indicator Observations of traffic on many roads had shown that vehicles tended to travel too close together for safety. One set of measurements showed that over half of all vehicles were travelling at less than 1 second intervals from the vehicle in front. A number of factors were involved in such situations. One was the inability of drivers to judge correctly the following distance they required for safe travel for particular speeds and road conditions.

It was also the case that the relative change in size of a vehicle to an observer must be above a certain mini mum level before he was able to detect that the vehicle was closing or going away from him. Thus a driver tended to travel at a distance from the vehicle in front where its size was such that he was capable of quickly detecting changes in its distance from him. At high speeds the optimum distance for detecting the onset of lead vehicle braking might be less than that necessary to allow the following driver to react in time.

The problem then was to devise a simple instrument which enabled the distance to be kept from the vehicle ahead to be shown as a function of the following vehicle's speed. This required an indicating device which could change its gauging distance continuously as a function of the driver's own speed. In addition it was important for the driver to be able to see the display superimposed on his view of the road ahead and focused in the same region as the vehicle being followed.

Making use of the HUD principle two vertical lines were projected onto the windscreen and by suitable focusing of the light the driver sees them in the road scene ahead. These lines then were separated by a distance which was controlled by the speed of the vehicle, ie the faster the speed of the vehicle the closer the two lines were together. In order to maintain a safe headway the driver had simply to adjust his distance so that the lines were roughly on the outside edges of the vehicle.

Automatic dimming

Some form of lighting was desirable on moving vehicles in all lighted streets so that road users were able to distinguish not only between moving and stationary vehicles but also to make better judgment as to the speed of approach. The degree of illumination required for this was clearly dictated by the level of street lighting. In poorly lit streets the full level of dipped headlights was required. In well lit streets a lower level than this was desirable since full lighting could be a considerable source of annoyance to other road users.

A manually controlled dim dip system was devised and tested in 1966. However, it had a number of objections, so it was decided to look into the possibility of developing a fully automatic headlight dimming system. This system would have to satisfy the following requirements: O Be insensitive to the headlights of other vehicles.

O Give a variable level of dimming ranging from no dimming at all where there was no street-lighting or poor street-lighting, to full dimming in good street-lighting.

O Dim at a slow rate but "brighten-up" at a fast rate as necessary when suddenly entering an unlit area.

0 Not dim headlights when they were switched on in daylight fog.

A system had now been developed that satisfied these requirements in that it responded only to the frequency of fluctuation of the light source in street lighting installations, ie 100 Hz. These fluctuations could not be detected by the human eye and did not, of course, occur in natural daylight nor in light from vehicle headlights. This device was being developed into a system suitable for mass production and a sufficient number would be produced to enable a fleet trial to be conducted to establish the quantitative effect on safety that might be expected if it were generally introduced.

Information systems

In accident avoidance the supply of information to the driver was a part of the safety system, but whether information systems had any effect at all without their enforcement by the law was very difficult to ascertain. Enforcement of regulations was effective only to the extent that it was possible and the cost could be accepted. Very briefly the, information could be given by signs and signals on the road or by more recent developments in the vehicle. Radio broadcasts could give information on road conditions over wide areas allowing route planning or the more localized transmissions could give details to vehicles about conditions on the road immediately ahead.

A well-known effect was that after driving continuously at high speed for some time, the speed appeared to de crease and then when slowing down the speed appeared to be slower still. Since this effect was caused by motion through the environment the question had to be, could the environment be altered to produce similar or reverse effects. Experiments on a simulator and on roads suggested that various patterns could be used that altered the driver's visual impression of speed.

. A pattern was developed by which, using visual information only, a driver could reduce his speed to a value very close to that which he required. One such pattern had been tried out on the roads for three years and continued to produce the desired speed changes. It had also given highly significant reductions in accidents. The existing pattern was produced for a particular set of road conditions. Research was now being directed towards producing patterns to alleviate conflicts and reduce speed in other situations. Fifty sites had been given the original line pattern and the reduction of accidents is under continuous review.

Rumble strips were developed to give drivers additional warning that they were approaching a hazard. This was done by generating a noticeable rumbling noise inside the vehicle. A surface to produce this noise level consisted of 13-19mm roadstones held in an epoxy binder. This increase in noise was judged to be very valuable by subjects who took part in the experiments. Three sites had been used for experimental purposes, but accident figures were only available for one site.

Lighting

So far, said Mr Prentice, he had been concerned with perceptual judgements of speed, relative motion etc. But in night-time driving, a more fundamental ability become important — the basic ability to see, whether this be seeing the run of the road, unlit obstacles or the various signs and markings which were patently visible in daylight.

It was useful to distinguish between lighting which was fundamentally for position and motion, and lighting which was for illumination, The former had already been mentioned in connection with the automatically dimmed headlamp; the latter included roadway lighting and vehicle headlights.

It was well established that adequate street lighting made a major contribution to the reduction of night-time accidents. Analysis of accidents suggested that the savings in the cost of accidents on 113km/ h (70mph) trunk roads could be as much as three times the cost of the lighting.

The introduction of lighting columns into the environment, however, could itself cause accidents. Lighting columns were now available for use which broke-off at ground level when struck by a vehicle, the column falling to the ground at the rear of the vehicle after impact.

Despite considerable progress in headlamp technology, the basic headlight problem of lighting the road ahead without dazzling the oncoming driver still remained. In the short-term, selflevelling of headlamps would improve the situation. In the longer term, novel headlamp systems, such as polarized light, would be needed to achieve significant improvements in a driver's ability to see.

Road layout

The unambiguous interpretation of the road system was vital to the road user. Accident statistics indicated various danger points, such as junctions, hidden hollows and corners, but this did not provide the information as to how they should be changed.

Changing a junction for example was expensive and when completed might not give the desired reduction in accidents, equally a new junction might not be satisfactory from a driver's viewpoint.

Research was going on into the use oi computer graphics to produce per, spective eye views of road layouts frorr the co-ordinates defining th( boundaries of the highway and all th( items that would be found on or near th( highway, ie street furniture, buildings This was expected to lead to Um portrayal in colour of real time con tinuous runs through a junction over ; range of speeds and viewing positions This would enable alterations to 13, made to the layout, ie elevation, stree furniture, angles of approach and tries out on many subjects so that the correc perceptual conditions could be estab lished before a new junction was de signed or an old one altered. The sam technique could clearly be applied t, any road scene.

There were clearly many other para meters which could influence drivin performance, for example trainini education, motivation, etc. The fac however, remained that as long a people had freedom of choice the would use the facilities they were give to the maximum; as road-holding vehicles improved, speed increased; C braking systems improved then brakin was left to a later time. So the questio that had to be asked was if the vehic occupant was so cocooned that he coul not be hurt below a certain speed woul he continue to drive at the same level ( risk as before and therefore would the be no decrease in the number of acc dents, but an increase?