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Publication Number: FHWA-HRT-04-136
Date: December 2005
Enhanced Night Visibility, Volume V: Phase II—Study 3: Visual Performance During Nighttime Driving in Snow
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A total of 240 observations were obtained from the experiment for each of the objective measurements, detection and recognition distances. An ANOVA was performed on both objective measurements using a 4 (VES) by 2 (Age) by 3 (Object) mixed factorial model. The ANOVA summary tables for both detection distance (table 6) and recognition distance (table 7) indicate that only the main effects for VES and object were significant for detection and recognition distances. The interactions and the main age effect were not significant at p < 0.05 (table 8).
The mean and standard error (SE) detection distances of the two age groups were as follows:
The mean and SE recognition distances were as follows:
The post hoc results for the significant main effects are shown as graphs in figure 9 and figure 10. Standard error bars are provided with the means, and means with the same letter in their grouping were not considered significantly different (based on the Bonferroni post hoc test).
The HLB headlamp is the most commonly available VES, making its experimental results a baseline measure; therefore, it is suggested that a comparison of the results of other VESs be made to results obtained for the HLB in the following descriptions of the significant results. Note that this is only one halogen headlamp type and beam pattern, and the results are not necessarily representative of all halogen headlamps currently on the market.
The VES main effect for both detection and recognition distances can be seen in figure 9. For detection distance, the supplemental UV–A showed a significant benefit over the baseline HLB. The average detection distance for the five UV–A + HLB configuration was 66.1 m (217 ft), and the detection distance for the hybrid UV–A + HLB was 62.2 m (204 ft). The detection distance for the HLB was 59.4 m (195 ft). Detection distances for all the VESs were significantly different than that for the HID configuration (51.2 m, 168 ft), which performed the worst. HID performed similarly on recognition distances, with both UV–A + HLB pairings and the HLB alone having significantly greater distances. The recognition distances for HLB and the HLB with supplemental UV–A were not significantly different from each other.
Figure 9. Bar graph. Bonferroni post-hoc results on detection and recognition
distances for the main effect: VES.
The post hoc results suggest that the clothing color (white versus black) determined the significant differences for the object main effect (figure 10). The detection distances of both the perpendicular and parallel pedestrians wearing white clothing—69.869.8 m (229 ft) and 69.2 m (227 ft), respectively—were significantly greater than the 39.9-m (131-ft) detection distance of the perpendicular pedestrian wearing black clothing. This suggests that, overall, the clothing color rather than the motion of the object caused the observed differences. These trends were also followed by the recognition distances, where the perpendicular and parallel pedestrians wearing white clothing—65.2 m (214 ft) and 64.3 m (211 ft), respectively—outperformed the 36.0-m (118-ft) detection distance for the perpendicular pedestrian wearing black clothing.
Figure 10. Bar graph. Bonferroni post-hoc results on detection and recognition
distances for the main effect: object.
An ANOVA was performed to analyze the subjective measurements using a 4 (VES) by 2 (Age) mixed factorial model. ANOVA summary tables were generated for each of the seven subjective statements, shown in table 9 through table 15. No significant difference was found for any of the statements. Missing values for statement 1 (one response), statement 5 (one response), and statement 6 (two responses) resulted in total degrees of freedom (DF) for these statements that were different from those of statements 2, 3, 4, and 7.
Table 9. ANOVA summary table for the Likert-type rating for detection.
Table 10. ANOVA summary table for the Likert-type rating for recognition.
Table 11. ANOVA summary table for the Likert-type rating for lane-keeping assistance.
Table 12. ANOVA summary table for the Likert-type rating for roadway direction.
Table 13. ANOVA summary table for the Likert-type rating for visual discomfort.
Table 14. ANOVA summary table for the Likert-type rating for overall safety rating.
Table 15. ANOVA summary table for the Likert-type rating for overall VES evaluation.
To understand drivers’ ratings of the various VESs in terms of safety and comfort, the results for all seven statements for every VES were sorted by ascending mean rating. Although not significant, drivers rated the five UV–A + HLB VES as the top configuration that allowed them to detect objects sooner (statement 1), allowed them to recognize objects sooner (statement 2), helped them stay on the road better (statement 3), and made them feel safer (statement 6); it was perceived as being a better VES than their regular headlights (statement 7). The hybrid UV–A + HLB configuration had the top rating for seeing the direction of the roadway (statement 4), and the HLB was rated as the top configuration for not causing any more visual discomfort than the participant’s regular headlights (statement 5).
It is interesting, although not statistically significant, that the HID was rated better than the HLB in all statements other than statement 4 (their averages were equal for statements 6 and 7), conflicting with the objective measurements. Although the subjective results were not significant, the conflicting results do exhibit the difference in driver perception and performance. The HLB was rated as the worst for detection, recognition, staying on the road, and seeing the road direction even though it significantly outperformed the HID on the objective measurements. Although it was the worst performer, the HID was the second-highest rated configuration with respect to feeling safer and being a better configuration than the participant’s regular headlights. Following are the results by statement.