Abstract
Purpose :
Impaired contrast sensitivity (ICS) may delay drivers’ responses to road hazards. Advanced Driver Assistance Systems that provide hazard warnings can mitigate crash risk; however, the benefits may vary with warning design. We tested 3 collision warning systems with different modalities and timing thresholds and evaluated their impact on the responses of drivers with ICS to pedestrian hazards in a simulator.
Methods :
To date, 13 subjects with normal vision (NV) (65–86 y, median CS 1.95) and 9 subjects with ICS (63–84 y, median CS 1.35 log units) participated. They completed 6 city drives with 3 warning conditions: auditory (pulse beeps), directional tactile (pulse vibrations on either left or right side), and non-directional tactile (pulse vibrations on both sides). For each condition, they completed one drive with early and one drive with late warnings, triggered when time-to-collision was 3.5s and 2s, respectively. There were 10 pedestrian hazards per drive that crossed the road from the left or right, requiring a braking response by the driver to avoid a collision.
Results :
ICS subjects triggered more early warnings (61 vs 54%) and late warnings (20 vs 7%) than NV subjects and had more collisions (3.8 vs 0%). When warnings were triggered (data pooled across groups), early warnings reduced time to fixate hazards (late 1.8 vs early 1.2s, p=0.02), reduced brake response times (2.7 vs 1.7s, p<0.001) and reduced collision rates (1.5 vs 0.5%). Brake times did not differ between the groups for early warnings; however, ICS subjects took 0.5 s longer to brake than NV subjects with late warnings (p=0.02) and still had a 15.4% collision rate. No collisions occurred for ICS subjects with early warnings. For late warnings, non-directional tactile warnings resulted in the lowest collision rates for ICS subjects (6% vs Auditory 20% vs Directional tactile 19%). For early warnings, modality had no effects on fixation and brake times of ICS subjects. Most subjects preferred early warnings (91%) and the directional tactile modality (73%).
Conclusions :
With early warnings, both groups were faster to fixate and brake for hazards and had low collision rates. In events with late warnings, ICS subjects were slow to brake resulting in high collision rates. These results suggest that ICS drivers will benefit more from earlier warnings. Warning modality may be important for late warnings.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.