6.1 Detection Distance. The mean DDs and standard deviations for the two PTs under all the lighting conditions are listed in Table 1. The DDs with standard errors are shown in Fig. 4.
A two-factor ANOVA with replication analysis was performed. The results are summarized in Table 2. The dependent variable was DD, and the independent variables were the seven conspicuity treatments (WRED, HVJ, RT, WRED_HVJ, WRED_RT, HVJ_RT, and CB) and two PTs (250 ms and 600 ms). The results obtained in the sunlight condition indicated that the two independent variables had interaction effects on the DD. The WRED_HVJ, WRED_RT, and HVJ_RT treatments had static and dynamic conditions compared to the other conspicuity treatments. A post hoc (Tukey HSD) analysis revealed a statistically significant difference between the WRED_HVJ and HVJ treatments for the PT of 250 ms as well as between the WRED_HVJ and WRED treatments for the PT of 600 ms. However, no statistically significant difference was observed between the RT treatment and the CB for any of the PTs. The DD of the WRED_HVJ treatment was significantly greater than that of the CB for all the PTs.
Table 1: DD (m) and standard deviations for the two PTs under the four lighting conditions.
|
Conspicuity
treatment
|
Sunlight
|
TW-CH
|
TW+CH
|
NCH
|
250 ms
|
WRED
|
67.67 ± 7.28
|
62.67 ± 6.40
|
62.33 ± 7.74
|
35.33 ± 5.07
|
HVJ
|
65.33 ± 8.60
|
51.33 ± 7.76
|
59.33 ± 7.85
|
37.67 ± 7.28
|
RT
|
48.33 ± 7.91
|
24.67 ± 5.07
|
49.00 ± 8.85
|
34.33 ± 5.04
|
WRED_HVJ
|
71.67 ± 5.92
|
63.67 ± 6.15
|
65.67 ± 5.68
|
40.33 ± 5.56
|
WRED_RT
|
68.67 ± 7.76
|
63.67 ± 6.15
|
62.67 ± 7.40
|
37.67 ± 4.30
|
HVJ_RT
|
66.00 ± 7.70
|
51.33 ± 7.30
|
61.00 ± 6.62
|
38.00 ± 7.15
|
CB
|
48.33 ± 6.48
|
24.67 ± 5.07
|
26.33 ± 4.90
|
24.33 ± 5.04
|
600 ms
|
WRED
|
138.33 ± 7.91
|
97.33 ± 7.85
|
94.33 ± 5.04
|
58.33 ± 7.91
|
HVJ
|
140.67 ± 10.81
|
89.67 ± 7.18
|
103.67 ± 7.65
|
158.67 ± 8.19
|
RT
|
89.67 ± 7.65
|
44.67 ± 5.07
|
110.33 ± 11.29
|
163.67 ± 7.65
|
WRED_HVJ
|
145.33 ± 8.19
|
98.67 ± 8.19
|
104.67 ± 6.29
|
158.67 ± 8.19
|
WRED_RT
|
139.00 ± 7.59
|
98.67 ± 7.30
|
110.67 ± 10.81
|
163.67 ± 7.65
|
HVJ_RT
|
140.67 ± 10.81
|
89.67 ± 7.18
|
112.67 ± 9.44
|
165.67 ± 6.26
|
CB
|
88.33 ± 7.91
|
44.67 ± 5.07
|
50.33 ± 8.90
|
40.33 ± 7.65
|
Table 2: Effects of PT and conspicuity treatments on DD.
|
Type
|
Lighting condition
|
Perception time (A)
|
Conspicuity treatment (B)
|
A*B
|
F
|
df
|
P
|
F
|
df
|
P
|
F
|
df
|
P
|
Detection
distance
|
Sunlight
|
6428.6
|
1, 406
|
***
|
277.5
|
6, 406
|
***
|
56.9
|
6, 406
|
***
|
TW-CH
|
2376.6
|
1, 406
|
***
|
599.4
|
6, 406
|
***
|
22.2
|
6, 406
|
***
|
TW+CH
|
3038.1
|
1, 406
|
***
|
279.8
|
6, 406
|
***
|
36.8
|
6, 406
|
***
|
NCH
|
20449.9
|
1, 406
|
***
|
1156.3
|
6, 406
|
***
|
864.6
|
6, 406
|
***
|
|
*** = significant at P<0.001
In the TW-CH condition, the two independent variables had significant interaction effects on the DD. More conspicuously, the combined WRED_HVJ and WRED_RT treatments had a greater impact on the DD in the TW-CH condition. A post hoc (Tukey HSD) analysis revealed no statistically significant difference between the WRED_HVJ treatment and both the WRED (P=0.996) and the WRED_RT (P=1.0) treatments for any of the PTs. Moreover, there was no statistically significant difference between the RT and the CB for any of the PTs. The DD of the WRED_HVJ and WRED_RT treatments was significantly greater than that of the CB for all the PTs.
The two independent variables had significant interaction effects on the DD under the TW+CH condition. The reflectivity along with the large conspicuous area of the treatments was advantageous for the DD under the TW+CH condition during the short perception time, and the reflectivity along with the dynamic behavior was advantageous during the perception time of 600 ms. A post hoc (Tukey HSD) analysis revealed no statistically significant difference between the WRED_HVJ treatment and the WRED (P=0.540), WRED_RT (P=0.661), and HVJ_RT (P=0.151) treatments for the PT of 250 ms.
Moreover, there was no statistically significant difference between the WRED_HVJ treatment and the HVJ (P=0.999), RT (P=0.162), and WRED_RT (P=0.115) treatments for the PT of 600 ms. The DD of the WRED_HVJ treatment was significantly greater than that of the CB for the PT of 250 ms; however, the DD of the HVJ_RT treatment was significantly greater than that of the CB for the PT of 600 ms
In the NCH condition, the two independent variables had significant interaction effects on the DD. The total reflective area and cyclic conditions influenced the DD. The large conspicuous area with reflectivity influenced the detection during the shortest PT. A post hoc (Tukey HSD) analysis revealed no statistically significant difference between the WRED_HVJ treatment and the HVJ (P=0.548), WRED_RT (P=0.548), and HVJ_RT (P=0.697) treatments for the PT of 250 ms. Moreover, there was no statistically significant difference between the WRED_HVJ treatment and the HVJ (P>0.05), RT (P>0.05), and WRED_RT (P>0.05) treatments for the PT of 600 ms. The DD of the WRED_HVJ treatment was significantly greater than that of the CB for the PT of 250 ms. However, the DD of the HVJ_RT treatment was significantly greater than that of the CB for the PT of 600 ms.
Both the self-generated color-blinking signal of the WRED and the additional conspicuous area of the reflective materials of the HVJ played a significant role in the detection of the bicycle within the shortest PT (250 ms) under all the lighting conditions. The DD of the WRED_HVJ treatment was significantly greater than that of the other conspicuity treatments under sunlight and TW-CH conditions for all the PTs. In addition, the DD of the WRED_HVJ treatment was greater under the TW+CH and NCH conditions for the PT of 250 ms, while the DD for the HVJ_RT treatment was significantly greater in the TW+CH and NCH conditions for the PT of 600 ms.
Table 3: RD (m) and standard deviations for the two PTs under the four lighting conditions.
|
Conspicuity
treatment
|
Sunlight
|
TW-CH
|
TW+CH
|
NCH
|
250 ms
|
WRED
|
51.33 ± 7.76
|
47.00 ± 4.66
|
49.33 ± 6.39
|
33.00 ± 6.51
|
HVJ
|
49.00 ± 9.23
|
43.67 ± 4.90
|
48.33 ± 6.99
|
36.33 ± 6.15
|
RT
|
41.67 ± 6.99
|
22.67 ± 4.49
|
44.67 ± 5.07
|
30.67 ± 8.68
|
WRED_HVJ
|
54.33 ± 8.58
|
47.00 ± 4.66
|
52.67 ± 5.20
|
38.67 ± 5.07
|
WRED_RT
|
52.33 ± 7.28
|
47.00 ± 4.66
|
50.00 ± 5.87
|
33.33 ± 6.61
|
HVJ_RT
|
50.00 ± 8.71
|
43.67 ± 4.90
|
50.33 ± 5.56
|
38.67 ± 5.07
|
CB
|
41.67 ± 8.34
|
22.67 ± 4.49
|
24.00 ± 4.98
|
20.33 ± 5.56
|
600 ms
|
WRED
|
94.67 ± 9.37
|
72.67 ± 7.85
|
74.67 ± 5.71
|
50.67 ± 7.40
|
HVJ
|
102.33 ± 8.58
|
68.33 ± 5.92
|
89.67 ± 9.28
|
98.67 ± 7.76
|
RT
|
71.67 ± 7.47
|
44.33 ± 7.28
|
88.67 ± 7.76
|
101.67 ± 7.47
|
WRED_HVJ
|
105.00 ± 5.72
|
74.33 ± 6.26
|
89.67 ± 9.28
|
98.67 ± 7.76
|
WRED_RT
|
94.67 ± 9.37
|
72.67 ± 7.85
|
88.67 ± 7.76
|
101.67 ± 7.47
|
HVJ_RT
|
102.33 ± 8.58
|
68.33 ± 5.92
|
93.33 ± 7.58
|
104.33 ± 6.79
|
CB
|
71.33 ± 6.29
|
44.33 ± 6.79
|
48.33 ± 7.47
|
40.00 ± 6.43
|
6.2 Recognition Distance. The mean RDs and standard deviations considering the two PTs under all the lighting conditions are listed in Table 3. The RDs with standard errors are shown in Fig. 5.
A two-factor ANOVA with replication analysis was performed. The results are summarized in Table 4. The dependent variable was RD, and the independent variables were the seven conspicuity treatments (WRED, HVJ, RT, WRED_HVJ, WRED_RT, HVJ_RT, and CB) and the two PTs (250 ms and 600 ms). The results obtained in the sunlight condition showed that the two independent variables had interaction effects on the RD. The WRED_HVJ treatment had static and dynamic conditions that allowed easy recognition of the bicycle compared to the other conspicuity treatments. A post hoc (Tukey HSD) analysis revealed no statistically significant difference between the WRED_HVJ treatment and the WRED (P=0.789), HVJ (P=0.154), WRED_RT (P=0.964), and HVJ_RT (P=0.383) treatments for the PT of 250 ms.
Table 4: Effects of PT and conspicuity treatments on RD.
|
Type
|
Lighting condition
|
Perception time (A)
|
Conspicuity treatment (B)
|
A*B
|
F
|
df
|
P
|
F
|
df
|
P
|
F
|
df
|
P
|
|
Recognition
distance
|
Sunlight
|
2976.0
|
1, 406
|
***
|
83.1
|
6, 406
|
***
|
22.9
|
6, 406
|
***
|
|
TW-CH
|
1814.7
|
1, 406
|
***
|
262.9
|
6, 406
|
***
|
1.94
|
6, 406
|
0.074
|
|
TW+CH
|
2875.3
|
1, 406
|
***
|
198.4
|
6, 406
|
***
|
20.8
|
6, 406
|
***
|
|
NCH
|
6082.8
|
1, 406
|
***
|
335.5
|
6, 406
|
***
|
171.3
|
6, 406
|
***
|
|
|
*** = significant at P<0.001
Moreover, there was no statistically significant difference between the WRED_HVJ treatment and the HVJ (P=0.857) and HVJ_RT (P=0.857) treatments for the PT of 600 ms. The RD for the WRED_HVJ treatment was significantly greater than that of the CB for all the PTs.
Under the TW-CH condition, the two independent variables had significant effects on the RD. The WRED treatment enhanced the bicycle recognition under the TW-CH condition. The RD of the WRED_HVJ treatment was significantly greater than that of the CB for all the PTs.
The two independent variables had significant interaction effects on the RD under the TW+CH condition. The large conspicuous area with reflectivity of the HVJ and the cyclic condition of the WRED treatment were advantageous within the PT of 250 ms. By contrast, the large reflective area and cyclic condition of the HVJ_RT treatment were effective for recognizing the bicycle in the PT of 600 ms. A post hoc (Tukey HSD) analysis revealed no statistically significant difference between the WRED_HVJ treatment and the WRED (P=0.280), WRED_RT (P=0.556), and HVJ_RT (P=0.704) treatments for the PT of 250 ms. In addition, there was no statistically significant difference between the WRED_HVJ treatment and the WRED_RT (P>0.990), HVJ (P>0.850), RT (P>0.992), and HVJ_RT (P>0.257) treatments for the PT of 600 ms. The RD of the WRED_HVJ treatment was significantly greater than that of the CB for the PT of 250 ms, and the RD of the HVJ_RT treatment was significantly greater than that of the CB for the PT of 600 ms.
In the NCH condition, the two independent variables had significant interaction effects on the RD. A post hoc (Tukey HSD) analysis revealed no statistically significant difference between the WRED_HVJ treatment and the HVJ (P=0.788) and HVJ_RT (P=1.0) treatments for the PT of 250 ms. Moreover, there was no statistically significant difference between the WRED_HVJ treatment and the HVJ (P>0.05), RT (P>0.05), WRED_RT (P>0.05), and HVJ_RT(P>0.05) treatments in the PT of 600 ms. The RD of the HVJ_RT treatment was significantly greater than that of the CB for all the PTs.
The combined effects of the WRED_HVJ and HVJ_RT treatments provided additional advantages for recognizing the bicycle within the shortest PT. The RD of the WRED_HVJ treatment was significantly greater for the PT of 250 ms under all the lighting conditions. In the sunlight and TW-CH conditions, the RD of the WRED_HVJ treatment was significantly greater for all the PTs. However, the RD of the HVJ_RT treatment was significantly greater for the PT of 600 ms under the TW+CH and NCH conditions.
6.3 Perception Time. A two-factor ANOVA with replication analysis was performed on the PT at a distance of 25 m from the camera. The dependent variable was PT, and the independent variables were the seven conspicuity treatments (WRED, HVJ, RT, WRED_HVJ, WRED_RT, HVJ_RT, and CB) and the four lighting conditions (sunlight, TW-CH, TW+CH, NCH). There was a statistically significant interaction between the conspicuity treatments and the lighting conditions The post hoc analysis revealed no statistically significant difference between the WRED_HVJ treatment and the WRED (P=0.737) and WRED_RT (P=0.737) treatments under the sunlight condition. The PT of the WRED_HVJ treatment (184.88 ± 4.64 ms, P<0.001) was significantly shorter than that of the CB (241.33 ± 10.78 ms) under the sunlight condition, as shown in Fig. 6(a). Under the TW-CH condition, the PT of the WRED_HVJ treatment (186.88 ± 6.25 ms, P<0.001) was significantly shorter than that of the CB (244.24 ± 10.03 ms), as shown in Fig. 6(b). There was no statistically significant difference between the WRED_HVJ treatment and the HVJ (P=0.394), WRED_RT (P=1.0), and HVJ_RT (P=0.694) treatments for the PT under the TW+CH condition. The PT of the WRED_HVJ treatment (205.69 ± 6.46 ms, P<0.001) was significantly shorter than that of the CB (264.13 ± 10.32 ms), as shown in Fig. 6(c). Under the NCH condition, there was no statistically significant difference between the WRED_HVJ treatment and the HVJ (P=1.0), WRED_RT (P=1.0), and HVJ_RT (P=1.0) treatments for the PT. The PT of the WRED_HVJ treatment (216.87 ± 6.93 ms, P<0.001) was significantly shorter than that of the CB (249.51 ± 10.03 ms), as shown in Fig. 6(d).
Under the sunlight and TW-CH conditions, the WRED, WRED_HVJ, and WRED_RT conspicuity treatments played a significant role in the detection of the bicycle within the shortest PT, and the mean PT was shorter than that of the other conspicuity treatments. However, under the TW+CH condition, the PT for detecting the bicycle was the shortest in the case of the WRED_HVJ and WRED_RT treatments. In addition, the PTs of the WRED_HVJ, WRED_RT, and HVJ_RT treatments were the shortest in the NCH condition.
In this study, the effectiveness of different conspicuity treatments and their combinations in detecting a bicycle within a short PT was evaluated on the basis of the self-signaling of a bicycle and its reflective area, as compared to a control. In comparison to the CB, the combined WRED_HVJ treatment resulted in an improvement in the DD and RD within the PT of 250 ms under all the lighting conditions. Moreover, the DD and RD of the WRED_HVJ treatment were significantly greater than those of the CB for all the PTs under the sunlight and TW-CH conditions. However, for the PT of 600 ms and under the TW+CH and NCH conditions, the DD and RD of the HVJ_RT treatment were significantly greater than those of the CB. Based on a residential road, a restricted speed of 30 km/h, and a safe driving distance of 25 m, the required PTs of different conspicuity treatments were evaluated. The PT of the combined WRED_HVJ treatment was significantly shorter under the sunlight, TW-CH, and TW+CH conditions compared to that of the other conspicuity treatments. By contrast, the PT of the HVJ_RT treatment was shorter under the NCH condition.