An Assessment of the Safety Effects of Roadside Barriers on Reducing Mountainous Crash Injury Severity

Table 6

Model results for flexible barriers crashes in 2018-2019.

Variables	Coefficient	t-stat	Pseudoelasticities (%)
			Severe injury (SI)	Minor injury (MI)	No injury (NI)
Constant (SI)	−1.663	−4.15	—	—	—
Constant (MI)	−1.414	−3.21	—	—	—
Random parameter (normally distributed)
Medium-low visibility indicator (1 if 50–100 meters; otherwise, 0) (NI)	2.068	2.95	−22.07	−22.07	8.63
Standard deviation of parameter density function	1.570	1.74
Dark-lighted indicator (1 if yes; otherwise, 0) (NI)	−2.660	−4.08	20.97	20.97	−22.66
Standard deviation of the parameter density function	1.822	2.04	—	—	—
Heterogeneity in the mean of random parameters
Medium-low visibility indicator (1 if 50–100 meters; otherwise, 0) (NI): road without isolation indicator (1 if yes; otherwise, 0)	−2.157	−3.13	—	—	—
Medium-low visibility indicator (1 if 50–100 meters; otherwise, 0) (NI): rainy/snowy/foggy indicator (1 if yes; otherwise, 0)	1.635	2.03	—	—	—
Medium-low visibility indicator (1 if 50–100 meters; otherwise, 0) (NI): winter indicator (1 if yes; otherwise, 0)	1.755	2.18	—	—	—
Dark-lighted indicator (1 if yes; otherwise, 0) (NI): head-on collision indicator (1 if yes; otherwise, 0)	2.748	2.04	—	—	—
Dark-lighted indicator (1 if yes; otherwise, 0) (NI): winter indicator (1 if yes; otherwise, 0)	−2.137	−2.68	—	—	—
Dark-lighted indicator (1 if yes; otherwise, 0) (NI): summer indicator (1 if yes; otherwise, 0)	1.925	2.52	—	—	—
Driver characteristics
Young driver indicator (1 if below 25-years-old; otherwise, 0) (SI)	−1.641	−2.09	−21.66	0.46	0.41
Driver under alcohol influence indicator (1 if yes; otherwise, 0) (SI)	−2.178	−3.90	−35.52	2.22	1.71
Driver under alcohol influence indicator (1 if yes; otherwise, 0) (NI)	−2.340	−5.63	9.44	9.44	−20.86
No seatbelt use indicator (1 if yes; otherwise, 0) (SI)	1.119	2.41	9.03	−2.89	−1.83
Vehicle characteristics
Truck indicator (1 if yes; otherwise, 0) (SI)	1.882	5.56	20.28	−8.22	−6.86
Improper braking and steering indicator (1 if yes; otherwise, 0) (SI)	−0.777	−2.15	−23.78	2.15	1.72
Speeding indicator (1 if yes; otherwise, 0) (NI)	0.945	3.41	−18.47	−18.47	4.23
Roadway characteristics
Road without isolation indicator (1 if yes; otherwise, 0) (NI)	1.025	4.04	−39.77	−39.77	18.27
Wet surface indicator (1 if yes; otherwise, 0) (MI)	1.087	2.86	−14.38	16.32	−8.67
Tunnel indicator (1 if yes; otherwise, 0) (MI)	−1.191	−4.41	31.69	−61.86	18.83
Intersection indicator (1 if yes; otherwise, 0) (NI)	0.966	2.51	−10.26	−10.26	2.91
Large downhill grade indicator (1 if −2% or less vertical grade; otherwise, 0) (SI)	2.327	4.44	5.14	−3.52	−3.08
Crash characteristics
Head-on collision indicator (1 if yes; otherwise, 0) (MI)	−1.514	−2.72	3.15	−15.12	1.45
Summer indicator (1 if yes; otherwise, 0) (SI)	−1.207	−2.97	−29.84	2.24	1.66
Sunny indicator (1 if yes; otherwise, 0) (SI)	−0.681	−1.94	−17.14	1.84	1.39
Low visibility indicator (1 if below 50 meters; otherwise, 0) (MI)	1.106	2.58	−4.38	5.55	−3.71
Medium visibility indicator (1 if 100–200 meters; otherwise, 0) (NI)	1.181	4.05	−12.62	−12.62	9.18
Dark-lighted indicator (1 if yes; otherwise, 0) (SI)	−3.828	−5.92	−134.05	3.04	1.15
Dark-no light indicator (1 if yes; otherwise, 0) (MI)	0.848	2.32	−4.00	8.20	−3.32
Number of observations above and below zero generated from the random parameters	Above zero		Below zero
Medium-low visibility indicator (1 if 50–100 meters; otherwise, 0) (NI)	72.91%		27.09%
Dark lighted indicator (1 if yes; otherwise, 0) (NI)	13.74%		86.26%
Goodness-of-fit measures
McFadden R-squared	0.484

, , ==> significance at 0.99, 0.95, and 0.90 level of confidence, respectively.