A simulator study of a critical frontal collision situation was conducted in order to examine usefulness of different warning modalities from a principal other vehicle (POV). In total, 48 participants drove 30 km while performing a secondary task, announced by a vibration in the seat, and experiencing light and/or sound warnings from oncoming traffic.
For comparison field measurements of light and horn sound levels were collected. The measurements were used for the implementations in the simulators graphics- and sound system respectively.
The study aims at providing basic understanding of driver responses to headlight and sound warning coming from another vehicle. A possible application is the implementation of systems for automatic activation of these warnings. Systems for automatic activation of brakes and steering are currently entering the market. These systems use proximity sensors to monitor the state of surrounding road users. Depending on the specific situation the effort/possibility to avoid or mitigate an accident may differ significantly between the principle road users of a pending collision, e.g. one road user (1) may easily avoid a collision while another (2) may not be able to do so. The only possibility for the second road user (2) to avoid a collision in such a situation is to issue a warning to the first (1), so that he/she may take evasive actions. Connecting the horn and the headlight to already existing sensor system, for automatic warning activation, is a cost effective means to provide such a warning. These types of warnings, could of course, also be triggered manually by the driver. The aim of this project is to evaluate the effectiveness of such a warning and also to validate if the warning between the road users is experienced as intended and whether the warning is an effective countermeasure for avoiding accidents.
There is limited research on how to design warning signals to avoid collision. In a simulator study auditory collision warnings with increasing intensity have been shown more effective than other types of auditory warnings (Gray, 2011). According to research regarding warning signals in general, auditory warnings should, if possible impart the nature of the events to the user. (Edworthy, 1995a). Research have also shown that people can match the frequency with which they respond to alarms to the false alarm rate, that increasing the perceived urgency of an alarm decreases reaction time and that increasing the number of modalities in which a warning is presented decreases reaction time. (Edworthy, 1995b)
Another objective of this study was to develop simulation technology for a realistic sensation of headlight glare and horn sound of an oncoming vehicle. The effect of using these signaling systems in a critical situation was then studied in the VTI simulator III (Nordmark, Jansson, Palmkvist, & Sehammar, 2004). The aim of the present study was to find a suitable warning signal, triggered by a first vehicle, which makes the driver of a second vehicle react fast enough to avoid a collision. It is important that the driver understands the message of the signal to be able to distinguish between “normal” horn and blink signals which are not time critical and this time critical warning. An additional cognitive task was used to distract the drivers to create a critical event.
The driving scenario was a rural road (70 kph speed limit) where the driver of a vehicle was distracted by means of a visual distraction task (reading and recalling letters from a screen placed at a relative large down angle (40-45 degrees), and then “pushed” across the median towards an oncoming vehicle, by introducing a steering angle in the simulated vehicle without submitting that information to the motion platform. The oncoming vehicle detects that the situation is critical and attempts to use headlight glare and horn sound to warn the driver of the vehicle that is drifting into oncoming traffic.
A within person design with four experimental warning conditions were used to evaluate the modality of the warning signals. Non critical noise and light signals from POV represented for example a greeting or a wish to make the driver aware of the headlight. The purpose of the non-critical signals was to evaluate if the driver understands the difference between the critical and non-critical signal. Measurements used to monitor driver behavior were lateral distance between the vehicles when passing, and driver reaction time (in term of steering wheel and brake pedal response). This was accompanied with subjective ratings during and after the test drive, both to evaluate the realism of the simulated event and the usefulness of the warning provided by the meeting vehicle.
The participants drove the Subject Vehicle (SV) with the instruction to drive as he or she usually does. In total, the participant experienced the critical event 5 times during this trip. Three different warning signals were presented, one at each event. The warning coming from the encountering vehicle was given through an automatic system triggering the horn and/or the lights of the POV. There was also a baseline event when no warning was given. The warning signals was presented in balanced order to avoid effects of which signal is presented first etc. The signal presented at the first event was also presented at the fifth event. This was to be able to investigate the learning effect. The non-critical noise and light signals were presented in the gaps between two warning signals.
The analysis is in process and will be completed in time for the full length paper submission. Preliminary results from the questionnaire show that participants have noticed the following warnings during the drive; sound (n=44), light (n=39), sound and light (n=32). Most participants think that the warnings were useful (n=31). Sound and vibration in the simulator is thought to be realistic. Participants are very positive to the announcement of the secondary task through a vibration in the seat. Most participants are positive to all three warning types; light (n=36), sound (n=31), light and sound (n=41).