Traffic psychology and driving simulator experiments

Here are a few abstracts of driving simulator experiments in Traffic Psychology.

EXPERIMENT 1: Speed Choice and Steering Behaviour in Curve Driving

The relation between speed choice and steering performance during curve negotiation was studied in a driving simulator. The hypothesis was that curve radius and steering competence both affect steering error during curve driving resulting in compensatory speed choice. In this, the control of safety margins was assumed to operate as a regulatory mechanism. Smaller curve radii resulted in a larger required steering wheel angle while steering error increased linearly with required steering wheel angle. This was compensated for by choosing a lower speed, such that the time-to-line crossing to the inner-lane boundary was constant over all curve radii examined. Steering competence was measured during straight road driving. Poorer steering competence also resulted in larger steering errors that were compensated for by choosing a lower speed such that the safety margin to the inner-lane boundary was unaffected by steering competence.

EXPERIMENT 2: Preferred time-headway in car-following and operational skills in expected braking reactions

In a simulator experiment the relation between preferred time-headway in steady-state car-following and operational competence in braking reactions was studied. The hypothe­sis that drivers with smaller preferred time-headways are able to react faster or generate a faster motor response per se was not confirmed. Also, no evidence was found for differences in perceptual processes related to the detection of braking by the lead vehicle be­tween short followers and drivers with a larger preferred time-headway. The results suggest that short followers generate a faster motor response when there is some uncertainty con­cerning the level and duration of decele­ration of the lead vehicle in case it brakes. The results suggest that short followers differ from long followers in the ability to transform visual feedback to a required motor response. However, the presence of brake lights is required for the relation between operational performance and choice of time-headway to hold, possibly because a change in feedback requirements, i.e. the absence of brake lights, is more detrimental for skilled performers.

EXPERIMENT 3: Choice of time-headway in car-following and the role of time-to-collision information in bra­king 

Time-headway (THW) during car-follo­wing and braking response were stu­died in a driving simulator from the per­specti­ve that behaviour on the tactical level (e.g. choice of THW) may be linked to ope­rational compe­tence of vehicle con­trol (e.g. bra­king) via a process of adapta­tion. Time-headway was con­sis­tent within dri­vers and con­stant over a range of speeds. Since time-headway repre­sents the time avai­lable to the driver to reach the same level of dece­lerati­on as the lead vehi­cle in case it brakes, it was studied whether choice of time-headway was related to skills underly­ing bra­king perfor­mance. The initiation and control of bra­king were both affec­ted by time-to-collision (TTC) at the moment the lead vehi­cle started to brake. This stro­ngly suppor­ted the idea that time-to-collisi­on informa­tion is used for jud­ging the moment to start bra­king and in the control of bra­king. No evidence was found that short followers differ from long follo­wers in the abili­ty to accura­tely per­ceive TTC. There was howe­ver eviden­ce that short follo­wers are better able to program the intensity of braking to required levels. Also, short followers tuned the control of braking better to the development of critica­lity in time during the braking process. It was conclu­ded that short follo­wers may dif­fer from long followers in programming and execu­tion of the braking respon­se.

EXPERIMENT 4: Time-headway in car-following and operational performance during unexpected braking

The relation between choice of time-headway during car-follo­wing and the quality of braking skills was studied in a driving simulator. The theoreti­cal perspective was that individual differen­ces in behaviour on the tactical level may be related to skills on the operational level of the driving task via a process of adaptation. In a sample of 16 young and middle-aged experienced drivers independent asses­sments were made of preferred time-headway and braking skill. Starting from modern theories of visual-motor learning, braking skill was analyzed in terms of a reaction time component, an open-loop visual-motor component, and a closed-loop visual-motor component involving the precise adjustment of braking (timing and force) to the situation. The efficiency of the visual-motor component of braking was a strong and significant predictor of time-headway in such a way that more efficient braking indicated a shorter preferred time-headway. This result appears to support the adaptation theory on an individual level.

 EXPERIMENT 5: The effects of deceleration on braking reactions as a function of preferred time-headway

The manoeuvre of braking for a decelerating lead vehicle was separated into three sequential processes that were manipulated independently. The initial time-headway to the lead vehicle at the moment it started to decelerate affected reaction time. Primary deceleration of the lead vehicle manipulated the duration of the open-loop phase. From the moment the driver touched the brake pedal, the deceleration of the lead vehicle was changed. This secondary deceleration was assumed to affect the closed-loop phase of braking. The hypothesis was that drivers who prefer a small time-headway during car-following (short followers) differ from drivers who prefer to follow at a large time-headway (long followers) in both the open- and closed-loop phases. In that case an interaction is expected between following group (short vs. long follo­wers) and primary deceleration on the duration of the open-loop phase and between following group and secondary deceleration on the duration of the closed-loop phase, the maximum brake force exerted and the number of movement corrections. In general terms, these predictions could not be confirmed. The lack of confirmation of the hypothesis is explained in terms of task characteristics that resulted in startle reactions and vigilance effects.

EXPERIMENT 6: Perceptual-motor skills and sensitivity to TTC as a function of preferred time-headway in car-following

Based on the results of previous experiments it was tested whether the sensitivity of the braking response to time-to-collision information differs as a function of preferred time-headway in car-following. In an experiment performed in a simulator time-to-collision was manipulated by  varying the level of deceleration of the lead vehicle with a pre-selected group of short and long followers. In addition, it was tested whether choice of time-headway is related to more general differences in perceptual-motor skills. It was found that short followers perform better at both lateral- and longitudinal tracking tasks and that the braking response of short followers is more sensitive to differences in time-to-collision. The results support the hypothesis that preferred time-headway is at least to some extent an adaptation to individual differences in operational braking performance and perceptual-motor skills.

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