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

Table 2

Descriptive statistics of explanatory variables.

Variables	2016-2017						2018-2019
	W-beam		Flexible		Trees		W-beam		Flexible		Trees
	Mean	SD	Mean	SD	Mean	SD	Mean	SD	Mean	SD	Mean	SD
Driver characteristics
Male indicator (1 if yes; otherwise, 0)	0.916	0.277	0.907	0.291	0.905	0.293	0.919	0.273	0.909	0.288	0.885	0.319
Middle age driver indicator (1 if 25–60 years old; otherwise, 0)	0.891	0.311	0.889	0.315	0.871	0.336	0.866	0.341	0.865	0.342	0.870	0.336
Young driver indicator (1 if below 25 years old; otherwise, 0)	0.109	0.311	0.111	0.315	0.129	0.336	0.134	0.341	0.135	0.342	0.130	0.336
Intermediate driving experience indicator (1 if 10–15 years; otherwise, 0)	0.202	0.401	0.199	0.399	0.195	0.396	0.166	0.372	0.146	0.354	0.150	0.357
Novice driving experience indicator (1 if 3–10 years; otherwise, 0)	0.495	0.500	0.531	0.499	0.514	0.500	0.545	0.498	0.579	0.494	0.566	0.496
Rookie driving experience indicator (1 if below 3 years; otherwise, 0)	0.128	0.334	0.132	0.339	0.108	0.311	0.111	0.315	0.107	0.309	0.110	0.314
Expert driving experience indicator (1 if above 15 years; otherwise, 0)	0.175	0.381	0.138	0.345	0.182	0.386	0.178	0.383	0.168	0.374	0.174	0.379
Driver seatbelt use indicator (1 if yes; otherwise, 0)	0.850	0.358	0.892	0.311	0.928	0.259	0.873	0.333	0.893	0.309	0.944	0.230
Driver under alcohol influence indicator (1 if yes; otherwise, 0)	0.154	0.361	0.162	0.369	0.178	0.382	0.188	0.391	0.173	0.379	0.204	0.403
Vehicle characteristics
Car indicator (1 if yes; otherwise, 0)	0.741	0.438	0.858	0.350	0.845	0.362	0.783	0.413	0.849	0.359	0.874	0.332
Truck indicator (1 if yes, 0 otherwise)	0.259	0.438	0.142	0.350	0.155	0.362	0.217	0.413	0.151	0.359	0.126	0.332
Improper braking and steering indicator (1 if yes; otherwise, 0)	0.442	0.497	0.462	0.499	0.423	0.494	0.408	0.492	0.334	0.472	0.137	0.344
Speeding indicator (1 if yes; otherwise, 0)	0.301	0.459	0.242	0.429	0.269	0.444	0.217	0.413	0.272	0.445	0.506	0.500
Improper lane changing indicator (1 if yes; otherwise, 0)	0.104	0.305	0.134	0.341	0.130	0.337	0.187	0.390	0.221	0.415	0.153	0.360
Local vehicle indicator (1 if yes; otherwise, 0)	0.865	0.342	0.921	0.270	0.915	0.279	0.872	0.334	0.908	0.290	0.924	0.264
Roadway characteristics
Road without isolation indicator (1 if yes; otherwise, 0)	0.316	0.465	0.669	0.471	0.206	0.405	0.352	0.478	0.669	0.471	0.210	0.407
Road in good condition indicator (1 if yes; otherwise, 0)	0.969	0.173	0.966	0.181	0.993	0.085	0.965	0.183	0.981	0.138	0.986	0.119
Dry surface indicator (1 if yes; otherwise, 0)	0.723	0.448	0.779	0.415	0.784	0.412	0.724	0.447	0.718	0.450	0.716	0.451
Intersection indicator (1 if yes; otherwise, 0)	0.155	0.362	0.200	0.400	0.175	0.380	0.171	0.377	0.167	0.373	0.133	0.340
Ramp indicator (1 if yes; otherwise, 0)	0.041	0.197	0.008	0.092	0.026	0.158	0.091	0.287	0.035	0.183	0.019	0.135
Homogeneous section indicator (1 if yes; otherwise, 0)	0.678	0.468	0.751	0.433	0.779	0.415	0.063	0.243	0.013	0.113	0.834	0.372
Tunnel indicator (1 if yes; otherwise, 0)	0.126	0.333	0.041	0.198	0.020	0.140	0.675	0.469	0.786	0.411	0.014	0.116
Small uphill grade indicator (1 if 0–2% vertical grade; otherwise, 0)	0.758	0.429	0.748	0.435	0.895	0.306	0.758	0.429	0.783	0.412	0.933	0.250
Small downhill grade indicator (1 if −2–0% vertical grade; otherwise, 0)	0.082	0.275	0.169	0.375	0.064	0.245	0.092	0.289	0.123	0.329	0.047	0.211
Large uphill grade indicator (1 if 2% or greater vertical grade; otherwise, 0)	0.062	0.241	0.042	0.201	0.037	0.190	0.049	0.215	0.056	0.231	0.020	0.138
Large downhill grade indicator (1 if −2% or less vertical grade; otherwise, 0)	0.098	0.297	0.041	0.198	0.004	0.060	0.102	0.302	0.037	0.189	0.001	0.029
Crash characteristics
Sideswipe indicator (1 if yes; otherwise, 0)	0.447	0.498	0.604	0.489	0.681	0.466	0.497	0.500	0.562	0.496	0.730	0.444
Head-on collision indicator (1 if yes; otherwise, 0)	0.089	0.286	0.092	0.289	0.036	0.188	0.111	0.315	0.121	0.326	0.195	0.397
Rear-end indicator (1 if yes; otherwise, 0)	0.362	0.481	0.185	0.388	0.196	0.397	0.318	0.466	0.191	0.394	0.020	0.141
Winter indicator (1 if yes; otherwise, 0)	0.254	0.436	0.193	0.395	0.127	0.333	0.223	0.416	0.232	0.423	0.221	0.415
Summer indicator (1 if yes; otherwise, 0)	0.267	0.443	0.270	0.444	0.344	0.475	0.256	0.437	0.266	0.442	0.250	0.433
Spring indicator (1 if yes; otherwise, 0)	0.199	0.400	0.220	0.414	0.266	0.442	0.291	0.455	0.268	0.443	0.302	0.460
Autumn indicator (1 if yes; otherwise, 0)	0.279	0.449	0.317	0.466	0.263	0.441	0.230	0.421	0.234	0.423	0.227	0.419
Sunny indicator (1 if yes; otherwise, 0)	0.278	0.448	0.308	0.462	0.254	0.436	0.292	0.455	0.279	0.449	0.249	0.433
Cloudy indicator (1 if yes; otherwise, 0)	0.527	0.500	0.546	0.498	0.608	0.488	0.542	0.499	0.542	0.499	0.579	0.494
Rainy/snowy/foggy indicator (1 if yes; otherwise, 0)	0.195	0.396	0.145	0.352	0.138	0.345	0.166	0.372	0.180	0.384	0.172	0.378
Low visibility indicator (1 if below 50 meters; otherwise, 0)	0.107	0.310	0.118	0.323	0.048	0.215	0.110	0.313	0.090	0.286	0.023	0.150
Medium-low visibility indicator (1 if 50–100 meters; otherwise, 0)	0.321	0.467	0.386	0.487	0.316	0.465	0.306	0.461	0.336	0.473	0.339	0.474
Medium visibility indicator (1 if 100–200; otherwise, 0)	0.331	0.471	0.321	0.467	0.405	0.491	0.247	0.431	0.294	0.456	0.393	0.489
High visibility indicator (1 if above 200 meters; otherwise, 0)	0.241	0.428	0.175	0.380	0.231	0.421	0.337	0.473	0.280	0.449	0.245	0.430
Daylight indicator (1 if yes; otherwise, 0)	0.443	0.497	0.468	0.499	0.448	0.498	0.486	0.500	0.498	0.500	0.442	0.497
Dark-lighted indicator (1 if yes; otherwise, 0)	0.352	0.478	0.380	0.486	0.490	0.500	0.312	0.464	0.358	0.480	0.512	0.500
Dark-no light indicator (1 if yes; otherwise, 0)	0.205	0.404	0.152	0.359	0.062	0.241	0.202	0.402	0.144	0.351	0.046	0.209
Temporal characteristics
Weekends indicator (1 if yes; otherwise, 0)	0.716	0.451	0.749	0.434	0.731	0.444	0.701	0.458	0.678	0.468	0.744	0.436
Weekdays indicator (1 if yes; otherwise, 0)	0.284	0.451	0.251	0.434	0.269	0.444	0.299	0.458	0.322	0.468	0.256	0.436
Morning peak indicator (1 if 7:00–8:59; otherwise, 0)	0.240	0.427	0.206	0.404	0.238	0.426	0.255	0.436	0.208	0.406	0.212	0.409
Night time off-peak indicator (1 if 19:30–23:59; otherwise, 0)	0.169	0.375	0.128	0.335	0.127	0.333	0.138	0.345	0.130	0.336	0.110	0.314
Early morning indicator (1 if 00:00–7:00; otherwise, 0)	0.086	0.280	0.120	0.325	0.118	0.322	0.127	0.333	0.168	0.374	0.103	0.304
Afternoon peak indicator (1 if 17:00–19:29; otherwise, 0)	0.344	0.475	0.341	0.474	0.337	0.473	0.276	0.447	0.295	0.456	0.344	0.475
Daytime off-peak indicator (1 if 9:00–16:59; otherwise, 0)	0.161	0.368	0.206	0.404	0.180	0.385	0.205	0.404	0.199	0.399	0.230	0.421