Errol R. Hoffmann

Review of Relationships Between Steering Wheel Reversal Rate and Driving Task Demand

Previous literature and some new data on the relationship between steering wheel reversal rate (SRR) and driving task demand are discussed in terms of a set of theoretical assumptions proposed by Macdonald and Hoffmann (1978). SRR is generally expected to increase with increasing task demand; however, several recent studies found a significant decrease in SRR. It is argued that whether the relationship is positive or negative depends on the level of task difficulty relative to the drivers capacity to cope with it.

The Effects of Restricted Preview on Driver Steering Control and Performance

Driver steering control and performance were studied for straight-lane driving under conditions of restricted far-sight distance. The far-sight distance necessary for the driver to adequately align the car was found to be 70 ft. and was independent of vehicle speeds of 20 and 30 m.p.h. With far-sight distances beyond 70 ft., there was no improvement in driver steering performance. Spectral analysis of steering wheel angle showed peaks in the frequency range 0.1 to 0.3 Hz. The value of the peak frequency was affected by allowed preview time, where preview time was far-sight distance divided by vehicle speed. Cross-correlation analysis suggested that the peaks were associated with the drivers control of vehicle heading angle. Higher frequency peaks were observed in the range 0.35 to 0.6 Hz. These peaks were more likely to occur under conditions of severely reduced preview.

STEERING REVERSALS AS A MEASURE OF DRIVER PERFORMANCE AND STEERING TASK DIFFICULTY

A review is made of past work in which steering reversal rates were used as a measure of driver performance. The data from two previously reported experiments carried out in a controlled situation, are used to compare steering reversal rates with other performance measures. It is shown that, while steering reversal rates correlate with other measures of control frequency, they do not necessarily correlate with measures of absolute steering performance. This result is consistent with the view that frequency characteristics provide a measure of steering task difficulty rather than steering performance. It is shown that, when considering steering task difficulty, care must be taken to differentiate between the difficulty imposed by the task constraints and the factors which affect the drivers ability to maintain a level of performance commensurate with those constraints.

Motorcycle conspicuity and traffic accidents

An analysis of data from 1508 motorcycle accidents obtained from Victoria Police files for the year 1974 indicates that inadequate motorcycle visibility is an associated factor in 64.5% of automobile/motorcycle collisions. It is the sole identifiable cause of 21.0% of collisions. The conspicuity of the front of the motorcycle is found to be vitally important in these accidents.

Fitts' Law with transmission delay

It is shown that a modified form of Fitts’ Law applies when there is a transmission delay between control movements and feedback of system response to the operator. The model predicts, and experiments verify, that a multiplicative relationship holds between movement time, Index of Difficulty (ID), and transmission delay. Movement time at constant ID is shown to increase linearly with delay, and linearly with ID at constant delay. The model indicates that lines of constant delay meet at a single point on the MT vs ID graph; experimental data show the same behaviour. The data indicate that a change in control strategy occurs at a delay time of about 0·7, possibly from a more continuous form of control to a wait-and-move strategy. The model predictions fit the data in both regions, but with different coefficients.

A model for movement time on data-entry keyboards

A model is presented for the effects of keyboard geometrical design on the movement time between keys, when the movements are carried out under visual control with single finger operation (such as on a data-entry keypad). It is shown that, for a given key centre spacing, the optimum key width occurs when the gap between adjacent keys is equal to the width of the finger pad (that part of the finger which is used for key actuation). Three experiments are reported related to keyboard design. In an experiment on. simulated keyboards and using five different probes (four metal probes of different widths and real fingers), it is found that results similar to the theoretical predictions are obtained in that a minimum in movement time occurs when the inter-key gap is about equal to the probe width. The effect is somewhat less with real fingers when compared with metal probes. In the second experiment, five real keyboards were tested with constant key spacing and with variable key size. A number of different ampli...

Strength of component principles determining direction of turn stereotypes-linear displays with rotary controls

Three experiments on direction of turn stereotypes are reported for (i) twodimensional horizontally moving displays (ii) three-dimensional display/control arrangements and (iii) the relationship between response times and the strength of stereotypes. In each case, equations were written for the strength of the stereotype (proportion of clockwise movements) in terms of the direction predicted by various principles; clockwise to increase, clockwise to the right, clockwise away, scale-side and Warricks for two-dimensional arrangements and modifications of these for three-dimensional arrangements. Solution of these equations gave the contribution of each principle to the strength of the overall stereotype. There were found to be strong effects of subject groups (engineers and psychologists) in the strength of component principles. The important result was that the strength of the stereotype was a linear sum of the strength of each contributing principle. The work was extended to the case of three-dimensional...

Analysis of Drivers' Control Movements

Driver control movements were studied in two simple steering tasks: driving along a straight lane and on a circular path. In both cases drivers were found to make most of their control movements within a fairly small frequency range. Spectral analysis shows peaks in spectral density in the range 0.15 to 0.3 Hz. for the circular course and 0.1 to 0.2 Hz. for most cases on the straight course. In a number of trials, secondary peaks occurred in the region 0.35 to 0.6 Hz. An attempt is made to explain these results in terms of the information being used by the driver to steer the car. In the circular-course experiment each driver drove the vehicle with three different steering ratios. Change of steering ratio did not show any consistent effect on the form of the spectrum of steering-wheel angle.

Finger Width Corrections in Fitts' Law: Implications for Speed-Accuracy Research

This note points out that using the finger as a test probe in a Fitts task may lead to misleading results, because of the increased target tolerance resulting from the width of the finger pad. An experiment demonstrates the need to use a corrected target width when calculating the index of difficulty; without this correction, information processing rates are overestimated. An example is given of a developmental study in which the finger pad size changes with age. The resulting changes in the calculated rates of information processing are shown to be markedly different for the different age groups.

Children's Estimates of Vehicle Approach Times

Eighty subjects in four age groups (5-6. 7-8, 9-10. adult) viewed a series of movie film clips of a vehicle approaching them along a roadway. Subjects estimated the time at which the vehicle would have passed them. With mean data. all age groups underestimated the time to arrival. with the underestimation decreasing with increasing age. The ability of subjects to scale time was strongly age dependent; the exponent in a Stevens power law relationship increased with age, as did the explained variance, Using r2= 0.5 as a criterion for the achievement of time scaling, the percentages in each age group reaching the criterion were 26, 48, 68. and 86 for the 5-6, 7-8, 9-10. and adult groups. respectively. The data suggest that children would reach adult performance at about 12 years of age.