Malte Risto

Assessing drivers ability to carry out headway advice in motorway car driving

In order to improve throughput on motorways, a headway advisory system is being developed. This system could enable drivers to choose their headway differently by providing in-vehicle advice. How well are drivers able to follow a time or a distance headway advice and what effect has vehicle speed and advised headway on their ability? To test this, a group of 20 participants completed nine headway adjustment tasks in a driving simulator experiment. Half of the participants received a time headway advice and half received a distance headway advice. The absolute difference between the advised and the chosen headway acted as a performance measure. In the experiment no performance difference could be found between the driver’s carrying out target headway and those carrying out distance headway advice. Furthermore increasing vehicle speed significantly reduced the driver’s ability to carry out headway advice. This effect was not found for target headway. High inter-driver difference in headway estimation led to high standard deviations in estimation error. Apart from reducing the average estimation error, the support system under development should also focus on reducing the variance in chosen headways.

Supporting driver headway choice: The effects of discrete headway feedback when following headway instructions

With specific headway instructions drivers are not able to attain the exact headways as instructed. In this study, the effects of discrete headway feedback (and the direction of headway adjustment) on headway accuracy for drivers carrying out time headway instructions were assessed experimentally. Two groups of each 10 participants (one receiving headway feedback; one control) carried out headway instructions in a driving simulator; increasing and decreasing their headway to a target headway of 2 s at speeds of 50, 80, and 100 km/h. The difference between the instructed and chosen headway was a measure for headway accuracy. The feedback group heard a sound signal at the moment that they crossed the distance of the instructed headway. Unsupported participants showed no significant difference in headway accuracy when increasing or decreasing headways. Discrete headway feedback had varying effects on headway choice accuracy. When participants decreased their headway, feedback led to higher accuracy. When increasing their headway, feedback led to a lower accuracy, compared to no headway feedback. Support did not affect drivers performance in maintaining the chosen headway. The present results suggest that (a) in its current form discrete headway feedback is not sufficient to improve the overall accuracy of chosen headways when carrying out headway instructions; (b) the effect of discrete headway feedback depends on the direction of headway adjustment.