Indicadores Dietéticos

3.4.2.1 Driving Simulator

The experiment took place in NITES2 (the Nottingham Integrated Transport and Environment Simulation facility) driving simulator. This is a fixed base driving simulator with a 180 degrees semi-circular projection screen 2 metres in height and 5 metres in diameter. A rear view was provided by a flat screen television placed behind the participant that could be viewed with a conventional rear view mirror (no side mirrors were present). This simulator provides all standard car controls, with the exception of a handbrake. Hazard responses were made via a pushbutton attached to the steering wheel (for both video and simulated hazards). For standard video-based hazard scenarios, participants remained in the simulator, but the rear screen was wheeled in front of them and videos were shown via a Sony DSR-11 MiniDV digital video recorder. When placed in front of participants the screen subtended approximately 20 degrees of visual angle – similar to what would be the case in a standard Hazard Perception test.

3.4.2.2 Physiological Equipment

The physiological data was recorded using a Biopac MP150. It consisted of a bio potential amplifier, which received input from three separate pre amplifiers (GSR100C, PPG100C and RSP100C). The GSR100C was connected to two skin conductance transducers (TSD203), which had isotonic recording electrode gel 101 and were attached to the participant’s fingers. The participants pulse was recorded using a finger mounted optical pulse transducer (TSD200) connecting to the PPG100C pre amplifier.

3.4.2.3 HP Videos

The stimuli consisted of 8 hazard perception videos provided by the UK Driving Standards Agency. These were taken from the licensed training material available with the Hazard perception test and each included one predetermined hazardous event. These were already coded with a hazard onset and offset time,

which are used to score performance on the UK hazard perception test. A button press in the first fifth of this time window provided the candidate with a score of 5, while scores in later windows receive lower scores, down to 1 for the last window and a score of 0 for presses that are made before the hazard onset, or after the hazard offset. Hazards videos lasted between 49 and 69 seconds (mean 59.9 seconds). Hazard window lengths lasted between 2 and 12 seconds (mean 6.7 seconds). Descriptions of the 8 hazards used can be found below in Table 3.1 and detailed timings can be found in table 3.2. All of the HP videos contained driving scenes that took place during the day and in dry conditions.

The official introduction from the UK HP test was also used in this study, for the purpose of explaining what the participants were required to do during the video-based HP test. The video contains a video commentary, which defines what a hazard is (“any object that may cause you, as the driver, to slow down or change direction) as well as explaining when the participant is required to do during the test. It also provides an example HP video clip, which is run through twice. The first time any potential driving hazards are circled in yellow, while the score-able hazard is circled in red. The video also provides information on the scoring window for the hazard and their reaction time in responding to the hazard is important, with responses falling outside of the window not receiving a score. The hazard is then repeated, this time without anything being circled, in order to give the participant the opportunity to practise responding to the driving hazard.

Table 3.1. Description and order of the video and simulated hazards used in the experiment, as well as the speed limits for those hazards.

Table 3.2. List of total hazard clip lengths and scoring window lengths for the 2 On the motorway, a car comes from the slip road and into the left

hand lane in front of the car

70 mph 3 Whilst taking a left hand turn into a suburban road with cars

parked on either side of the road, a car enters the street from the right hand side

20 mph

4 When driving behind a motorcyclist, a bike pulls out from the pavement onto the road from the left hand side behind a red land rover, the motorcyclist proceeds to brake suddenly

30 mph

5 A pedestrian is walking on the left pavement beside a parked white van. They then step out into the road from behind the van and cross the road towards another pedestrian

20 mph

6 When following a cyclist who has come from a side street, a parked car then pulls out and forces the cyclist to swerve to avoid it

30 mph

7 A motorbike pulls out into the road heading towards you from a side street on the left. It passes a parked car on the side of the road by moving into your lane

30 mph

8 When following a car in front, a cyclist pulls out into the road in front of the car causing it to brake and slow down.

30 mph

3.4.2.4 Driving Simulations

Simulated versions of these eight hazards were also created for use in the driving simulator. In each case the behaviour of other vehicles in the simulator was matched to those in the video-based hazard. No attempt was made to precisely match the exact environmental geometry of the videoed hazards; instead we focused on ensuring the visual precursors to the hazard we accurately simulated.

Because a simulated drive will always vary from participant to participant depending on their driving behaviour, we could not match exact hazard timings, instead we defined fixed hazard onset and offset locations (in the simulated driving space) that would match those in the videos where the driver was proceeding at the prevailing speed limit. Although rear-view information was available in the simulated condition, no relevant vehicles were present behind the driver in any of the simulated hazards. The simulated hazards were designed to have the same total and scoring window durations as the video hazards when driven through at the speed limit. However, due to differences in the speed at which people drove in driving simulator, there were slight differences in these values for the participants.

All of the driving simulations took place in daytime with dry conditions.

3.4.2.5 Simulator Sickness Questionnaire

A standardised simulator sickness questionnaire was used to assess simulator sickness levels in the participants. It can be found in Appendix 3.1.