Samuel G. Charlton

Driving while conversing: Cell phones that distract and passengers who react

The research systematically compared the driving performance and conversational patterns of drivers speaking with in-car passengers, hands-free cell phones, and remote passengers who could see the drivers current driving situation (via a window into a driving simulator). Driving performance suffered during cell phone and remote passenger conversations as compared with in-car passenger conversations and no-conversation controls in terms of their approach speeds, reaction times, and avoidance of road and traffic hazards. Of particular interest was the phenomenon of conversation suppression, the tendency for passengers to slow their rates of conversation as the driver approached a hazard. On some occasions these passengers also offered alerting comments, warning the driver of an approaching hazard. Neither conversation suppression nor alerting comments were present during cell phone conversations. Remote passengers displayed low levels of alerting comments and conversation suppression, but not enough to avoid negative effects on driving performance. The data suggested that conversation modulation was a key factor in maintaining driving performance and that seeing the road and traffic was not sufficient to produce it. A second experiment investigated whether a cell phone modified to emit warning tones could alleviate some of the adverse effects typically associated with cell phone conversations. The modified cell phone produced discourse patterns that were similar to passenger conversations and driving performance nearly as good as that of drivers who were not conversing. This latter finding supported the argument that conversation modulation is a key ingredient in avoiding adverse effects of conversations with drivers, rather than the physical presence of an in-car passenger.

The effect of cell phone type on drivers subjective workload during concurrent driving and conversing.

The effect of three types of cell phones (hand held, hands free with an external speaker and personal hands free) on total subjective workload (including its constituent components; mental demand, physical demand, temporal demand, performance, effort and frustration) and intelligibility was measured using the NASA-task load index (TLX) and the modified rhyme test (MRT), respectively in 13 experienced drivers (nine male, four female, age range 28-65 years), whilst driving on a rural highway. The drivers rated all components of workload for each type of cell phone to be significantly higher than for a control condition in which no cell phone was used. The mean (standard deviation) total workload was lowest for the personal hands free cell phone (7.1(3.65)) and highest for the hands free speaker phone (10.8 (3.63)) (P<0.001). The mean (standard deviation) intelligibility score was highest for the personal hands free cell phone (74.1 (7.9)) and lowest for the hands free speaker phone (55.0 (10.4)) (P<0.001). Frustration was significantly correlated with total workload (0.60, P<0.001) and intelligibility was significantly correlated with frustration (-0.35, P<0.05). Physical demand was not a high contributor to total workload. It is concluded that a personal hands free cell phone would interfere least with the cognitive demands of driving.

Road user behaviour changes following a self-explaining roads intervention

The self-explaining roads (SER) approach uses road designs that evoke correct expectations and driving behaviours from road users to create a safe and user-friendly road network. Following the implementation of an SER process and retrofitting of local and collector roads in a suburb within Auckland City, lower speeds on local roads and less variation in speed on both local and collector roads were achieved, along with a closer match between actual and perceived safe speeds. Preliminary analyses of crash data shows that the project has resulted in a 30% reduction crash numbers and an 86% reduction in crash costs per annum, since the road changes were completed. In order to further understand the outcomes from this project, a study was carried out to measure the effects of the SER intervention on the activity and behaviour of all road users. Video was collected over nine separate days, at nine different locations, both before and after SER construction. Road user behaviour categories were developed for all potential road users at different location types and then used to code the video data. Following SER construction, on local roads there was a relatively higher proportion of pedestrians, less uniformity in vehicle lane keeping and less indicating by motorists along with less through traffic, reflecting a more informal/low speed local road environment. Pedestrians were less constrained on local roads following SER construction, possibly reflecting a perceptually safer and more user-friendly environment. These behaviours were not generally evident on collector roads, a trend also shown by the previous study of speed changes. Given that one of the objectives of SER is to match road user behaviour with functionally different road categories, the road user behaviour differences demonstrated on different road types within the SER trial area provides further reinforcement of a successful SER trial.

The effects of moderate alcohol concentrations on driving and cognitive performance during ascending and descending blood alcohol concentrations

Alcohol has an adverse effect on driving performance; however, the effects of moderate doses on different aspects of the driving task are inconsistent and differ across the intoxication curve. This research aimed to investigate driving and cognitive performance asymmetries (acute tolerance and acute protracted error) accompanying the onset and recovery from moderate alcohol consumption.

Driving with ADHD: performance effects and environment demand in traffic

Objective: This research investigated the on-road driving performance of individuals with ADHD across a range of road and traffic conditions to determine whether errors were linked to situational complexity and attentional demands. Method: The everyday driving performance of medicated drivers with ADHD, unmedicated drivers with ADHD, and controls was tested in urban, residential, rural, and highway environments using driver license testing procedures. Results: Unmedicated drivers with ADHD displayed fewer safe driving skills and committed more inattentive and impatient driving errors, particularly in low demand highway and rural driving conditions. Medicated drivers’ performance was not reliably different than controls. Participants in both ADHD groups were more likely than controls to report risky driving and involvement in crashes. Conclusion: The results demonstrate that situations with low attentional demand are particularly risky for unmedicated ADHD drivers and suggest that focus on these situations may be useful in improving driving outcomes for this population.

Fixating on the size-speed illusion of approaching railway trains: What we can learn from our eye movements

Railway level crossing collisions have recently been linked to a size-speed illusion where larger objects such as trains appear to move slower than smaller objects such as cars. An explanation for this illusion has centred on observer eye movements - particularly in relation to the larger, longer train. A previous study (Clark et al., 2016) found participants tend to make initial fixations to locations around the visual centroid of a moving vehicle; however individual eye movement patterns tended to be either fixation-saccade-fixation type, or smooth pursuit. It is therefore unknown as to which type of eye movement contributes to the size-speed illusion. This study isolated fixation eye movements by requiring participants to view computer animated sequences in a laboratory setting, where a static fixation square was placed in the foreground at one of two locations on a train (front and centroid). Results showed that even with the square placed around the front location of a vehicle, participants still underestimated the speed of the train relative to the car and underestimation was greater when the square was placed around the visual centroid of the train. Our results verify that manipulation of eye movement behaviour can be effective in reducing the magnitude of the size-speed illusion and propose that interventions based on this manipulation should be designed and tested for effectiveness.

The Development of a New Zealand Road Safety Laboratory

This paper describes the development of a road safety laboratory and the findngs to date of three of our research programs: (1) Testing the relative conspicuity of road workcrs’ safety garments. This study compared eight different colors and patterns of safety vests in real-life traffic scenes using rural and urban backgrounds. In a simulated dnving task, participants were asked to scan several road scenes with their peripheral vision to locate road workers wearing differently colored safety vests. Fluorescent orange and yellow vests were found to be the most visible. against any background, as compared to any other color or pattern of safety vest. (2) Teaching appropriate eye scanning patterns to novice dnvcrs. This project aims to determine whether the introduction of specific road scanning cues will result i n an improvement in performance during the negotiation of curves. Inexperienced drivers were seated in a driving simulator and were provided with dynamic target points superimposed on the road scene. Training with a dynamic target point located on the inside tangent of curves was found to iniprovc driving performance during tests where the cue was absent. (3) The effect of driver workload on situation awareness and driving performance. Participants in a driving simulator Kcre asked to complete three scenarios containing a variety of typical roadside objects and traffic. The data have revealed a close relationship between dnving, workload. and situation awareness such that moderate levels of cognitive workload are associated with better driving and situation awareness than high or low workload.