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Publication Number: FHWA-HRT-04-145
Date: December 2005

Enhanced Night Visibility Series, Volume XIV: Phase III—Study 2: Comparison of Near Infrared, Far Infrared, and Halogen Headlamps on Object Detection in Nighttime Rain

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APPENDIX J—RESULTS FOR ANOVA WITHOUT THE LOW/WIDE VES

In order to assess the influence of the low/wide VES on the original results, a secondary analysis was performed. This analysis used the same models, excluding the low/wide VES, as the original analysis of the detection distance, illuminance at the driver’s eye, and deBoer glare rating as discussed in the Results section.

The significant main effects and interactions for each dependent variable are marked with an “x” in table 18. The effect of pedestrian location and its interactions were not applicable to the deBoer glare ratings. The secondary ANOVA indicated no changes in significant difference for the detection distance or the deBoer glare ratings. Not surprisingly, with the exception of the Pedestrian by VES interaction, all the significant interactions in the original analysis (indicated by a dash in table 18) were not significant in this analysis.

Table 18. Secondary analysis ANOVA significant main effects and interactions.
Source Disability Glare Detection Distances Disability Glare Driver’s Eye Illuminance Discomfort
Glare deBoer Scale Ratings
Between
Age x x  
Participant (Age)      
 
Within
VES x x x
VES by Age    
VES by Participant (Age)      
 
Adaptation      
Adaptation by Age      
Adaptation by Participant (Age)      
 
VES by Adaptation      
VES by Adaptation by Age      
VES by Adaptation by Participant (Age)      
 
Pedestrian x x  
Pedestrian by Age    
Pedestrian by Participant (Age)      
 
Pedestrian by VES x x  
Pedestrian by VES by Age    
Pedestrian by VES by Participant (Age)      
 
Pedestrian by Adaptation      
Pedestrian by Adaptation by Age      
Pedestrian by Adaptation by Participant (Age)      
 
Pedestrian by VES by Adaptation      
Pedestrian by VES by Adaptation by Age      
Pedestrian by VES by Adaptation by Participant (Age)      

 

DEBOER SCALE RATINGS

Table 19 shows the secondary ANOVA results for the deBoer glare ratings. Only the main effect of VES glare (VES) was significant for the subjective measure of discomfort (p < 0.05). Results of a post hoc analysis of this main effect, shown in table 20, show no differences between the results of the original analysis and the secondary analysis.

Table 19. Secondary analysis ANOVA table for discomfort glare rating.
Source DF SS MS F Value P Value  
ADJUSTED TOTALS 239 2029.4       
Between
Age 2 89.6 44.8 1.24 0.3054  
Participant (Age) 27 975.0 36.1     
 
Within
VES 3 252.2 84.1 17.00 <.0001 *
VES by Age 6 45.1 7.5 1.52 0.1825  
VES by Participant (Age) 81 400.5 4.9     
 
Adaptation 1 1.0 1.0 0.23 0.6390  
Adaptation by Age 2 6.3 3.2 0.71 0.5029  
Adaptation by Participant (Age) 27 120.9 4.5     
 
VES by Adaptation 3 1.5 0.5 0.30 0.8252  
VES by Adaptation by Age 6 3.1 0.5 0.31 0.9299  
VES by Adaptation by Participant (Age) 81 134.2 1.66     

 

Table 20. Discomfort glare SNK groupings comparison for the VES main effect.
VES N Mean deBoer Rating Original SNK Grouping Secondary SNK Grouping
Low/Narrow 60 5.15 C C
Low/Wide 60 6.77 AB n/a
Medium/Medium 60 7.20 A A
High/Narrow 60 6.15 B B
High/Wide 60 6.15 B B

DETECTION DISTANCE

Table 21 shows results of the secondary ANOVA for detection distance. The significant results of the original analysis and the secondary analysis were the same: a significant two-way interaction—Pedestrian by VES—and three main effects—age, VES, and pedestrian location.

Table 21. Secondary analysis ANOVA table for detection distances.
Source DF SS MS F Value P Value  
ADJUSTED TOTALS 478 11092405       
Between
Age 2 1148008.3 574004.2 13.97 <.0001 *
Participant (Age) 27 1109334.1 41086.4     
 
Within
VES 3 1053434.8 351144.9 30.43 <.0001 *
VES by Age 6 56419.2 9403.2 0.81 0.5615  
VES by Participant (Age) 81 934660.3 11539.0     
 
Adaptation 1 125.2 125.2 0.02 0.8975  
Adaptation by Age 2 18931.1 9465.5 1.28 0.2946  
Adaptation by Participant (Age) 27 199776.1 7399.1     
 
Pedestrian 1 3555805.6 3555805.6 91.93 <.0001 *
Pedestrian by Age 2 91456.5 45728.2 1.18 0.3220  
Pedestrian by Participant (Age) 27 1044345.4 38679.5     
 
VES by Adaptation 3 3302.3 1100.8 0.19 0.9041  
VES by Adaptation by Age 6 23820.4 3970.1 0.68 0.6668  
VES by Adaptation by Participant (Age) 81 473474.6 5845.4     
 
Pedestrian by VES 3 210072.9 70024.3 9.62 <.0001 *
Pedestrian by VES by Age 6 11041.0 1840.2 0.25 0.9568  
Pedestrian by VES by Participant (Age) 81 589729.2 7280.6     
 
Pedestrian by Adaptation 1 13875.4 13875.4 3.82 0.0612  
Pedestrian by Adaptation by Age 2 6012.8 3006.4 0.83 0.4481  
Pedestrian by Adaptation by Participant (Age) 27 98138.4 3634.8     
 
Pedestrian by VES by Adaptation 3 2462.9 821.0 0.15 0.9297  
Pedestrian by VES by Adaptation by Age 6 8975.1 1495.8 0.27 0.9483  
Pedestrian VES by Adaptation by Participant (Age) 80 439203.2 5490.0     

 

Pedestrian by VES Interaction

The significant interaction of pedestrian location and VES is illustrated in figure 27. The results are the same between the original analysis and the secondary analysis. The low/narrow VES had the lowest detection distance for both the pedestrian on the left and the pedestrian on the right. The other VESs had similar distances to each other for the pedestrian on the left; however, the pedestrian on the right appeared to have longer detection with the medium/medium VES, which was rated as less glaring on the deBoer scale.

Bar graph. Secondary analysis mean detection distances for the interaction of pedestrian and VES. Click here for more detail.
Figure 27. Bar graph. Secondary analysis mean detection distances for the interaction of pedestrian and VES.

VES Main Effect

The secondary analysis found the main effect of VES to be significant (p < 0.05). Post hoc analyses for the original and secondary analyses indicated the same results (table 22).

Table 22. Detection distance SNK groupings comparison for the VES main effect.
VES N Mean Detection Distance (ft) Original SNK Grouping Secondary SNK Grouping
Low/Narrow 120 219 C C
Low/Wide 120 362 A n/a
Medium/Medium 120 354 A A
High/Narrow 119 321 B B
High/Wide 120 308 B B

Pedestrian Main Effect

The main effect of pedestrian position was significant (p < 0.05) in the secondary analysis. In the original analysis, the left pedestrian yielded a mean detection distance of 67.7 m (222 ft) and the right pedestrian a much farther detection distance of 122.8 m (403 ft). The secondary analysis indicated a similar result: left pedestrian at 64.4 m (211 ft) and right pedestrian at 117.1 m (384 ft).

Age Main Effect

The secondary analysis also found the main effect of age to be significant (p < 0.05). In both the original and secondary analyses, the post hoc SNK indicated that as age increased, detection distance significantly decreased. These results and both analyses’ means are shown in table 23.

Table 23. Detection distance SNK groupings comparison for the age main effect.
Age N Original Mean Detection Distance (ft) Secondary Mean Detection Distance (ft) Original SNK Grouping Secondary SNK Grouping
Young 160 376 358 A A
Middle-Aged 160 313 298 B B
Older 160 252 237 C C

DRIVER’S EYE ILLUMINANCE MEASUREMENTS

Table 24 shows secondary analysis ANOVA results of the illuminance at the driver’s eye. The significant results were the same as those for the original analysis for the main effects and the Pedestrian by VES interaction; however, the original analysis’ significant results that could be tied directly to the possible change in the low/wide VES were not significant in the secondary analysis. Specifically, the three-way interaction Pedestrian by VES by Age and the two-way interactions Pedestrian by Age and VES by Age were not significant in this analysis.

Table 24. Secondary analysis ANOVA table for the objective measurement of driver’s eye illuminance.
Source DF SS MS F Value P Value  
ADJUSTED TOTALS 479 492.5       
Between
Age 2 21.5 10.7 10.64 0.0004 *
Participant (Age) 27 27.2 1.0     
 
Within
VES 3 173.7 57.9 86.76 <.0001 *
VES by Age 6 4.8 0.8 1.19 0.3205  
VES by Participant (Age) 81 54.1 0.7     
 
Adaptation 1 0.0 0.0 0.01 0.9295 
Adaptation by Age 2 0.7 0.3 1.61 0.2186 
Adaptation by Participant (Age) 27 5.8 0.2     
 
Pedestrian 1 28.1 28.1 65.19 <.0001 *
Pedestrian by Age 2 0.3 0.2 0.36 0.6989  
Pedestrian by Participant (Age) 27 11.6 0.4     
 
VES by Adaptation 3 0.7 0.2 0.37 0.7772  
VES by Adaptation by Age 6 0.8 0.1 0.23 0.9672  
VES by Adaptation by Participant (Age) 81 50.5 0.6     
 
Pedestrian by VES 3 34.3 11.4 32.78 <.0001 *
Pedestrian by VES by Age 6 2.0 0.3 0.95 0.4642  
Pedestrian by VES by Participant (Age) 81 28.3 0.3     
 
Pedestrian by Adaptation 1 0.2 0.2 0.39 0.5351  
Pedestrian by Adaptation by Age 2 1.9 0.9 1.98 0.1582  
Pedestrian by Adaptation by Participant (Age) 27 12.9 0.5     
 
Pedestrian by VES by Adaptation 3 0.6 0.2 0.55 0.6525  
Pedestrian by VES by Adaptation by Age 6 1.3 0.2 0.54 0.7730  
Pedestrian VES by Adaptation by Participant (Age) 81 31.2 0.4     

Pedestrian by VES Interaction

The significant interaction of Pedestrian by VES is shown in figure 28. As in the original analysis, the wide-beam VES had the largest illuminance at detection of the left pedestrian, which was also more than three times that of the VES’s illuminance at detection of the right pedestrian. The medium/medium VES also seemed to follow this trend; however, both the narrow-beam VESs had similar illuminances at the point of detection for both the left and right pedestrians.

Bar graph. Mean illuminance readings (lx) at moment of detection for the Pedestrian by VES interaction without the low/wide VES. Click here for more detail.

Figure 28. Bar graph. Mean illuminance readings (lx) at moment of detection for the Pedestrian by VES interaction without the low/wide VES.

VES Main Effect

The secondary SNK post hoc test of VES indicated the same three significantly different groupings of driver’s eye illuminance (delta symbol lux) among the VESs (table 25). The low/narrow VES produced the highest mean driver’s eye illuminance level at detection, 1.93 lx. The wide-beam VES was in the second group with the second highest illuminance at detection. The medium/medium VES and high/narrow VES were grouped together with the lowest illuminance at detection (0.46 lx and 0.54 lx, respectively).

Table 25. Illuminance SNK groupings comparison for the VES main effect.
VES N Mean Illuminance (lx) Original SNK Grouping Secondary SNK Grouping
Low/Narrow 120 1.93 A A
Low/Wide 120 1.44 B n/a
Medium/Medium 120 0.46 C C
High/Narrow 120 0.54 C C
High/Wide 120 1.31 B B

Pedestrian Main Effect

The main effect of pedestrian location was also similar between the original analysis and the secondary analysis. Originally, the left-pedestrian location had a mean illumination level at detection of 1.52 lx. The mean illumination level for the right pedestrian was approximately half as great, 0.75 lx. In the secondary analysis, the illumination for the left was 1.30 lx, and for the right it was 0.82 lx.

Age Main Effect

The significant main effect of age is shown in table 26. In both the original and secondary analyses, as age increased, illumination at detection increased. However, the original post hoc analysis did not indicate a significant difference between younger and middle-aged drivers whereas the secondary analysis indicated that each age group was statistically different.

Table 26. Illuminance SNK groupings comparison for the age main effect.
Age N Original Mean Illuminance (lx) Secondary Mean Illuminance (lx) Original SNK Grouping Secondary SNK Grouping
Young 160 0.77 0.80 B C
Middle-Aged 160 0.93 1.06 B B
Older 160 1.72 1.32 A A

 

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