Analysis of Injury Severity of Drivers Involved Different Types of Two-Vehicle Crashes Using Random-Parameters Logit Models with Heterogeneity in Means and Variances

Table 2

Descriptive statistics of significant variables in the injury-severity model.

Variables	Car-car		Truck-truck		Car-truck		Car-truck
	CD		TD		CD		TD
	Mean	SD	Mean	SD	Mean	SD	Mean	SD
Day of week (1 if weekdays, 0 otherwise)	0.687	0.464	0.797	0.402	0.717	0.451	0.717	0.451
Day of week (1 if weekends, 0 otherwise)	0.313	0.464	0.203	0.402	0.283	0.451	0.283	0.451
Road type (1 if roundabout, 0 otherwise)	0.033	0.178	0.015	0.120	0.031	0.174	0.031	0.174
Road type (1 if one-way street, 0 otherwise)	0.006	0.077	0.003	0.054	0.003	0.058	0.003	0.058
Road type (1 if dual carriageway, 0 otherwise)	0.173	0.378	0.410	0.492	0.191	0.393	0.191	0.393
Road type (1 if single carriageway, 0 otherwise)	0.777	0.416	0.555	0.497	0.762	0.426	0.762	0.426
Road type (1 if slip road, 0 otherwise)	0.010	0.100	0.015	0.120	0.010	0.098	0.010	0.098
Road type (1 if unknown, 0 otherwise)	0.001	0.028	0.003	0.054	0.003	0.058	0.003	0.058
Speed limit (1 if 20 mph, 0 otherwise)	0.027	0.163	0.021	0.142	0.013	0.113	0.013	0.113
Speed limit (1 if 30 mph, 0 otherwise)	0.473	0.499	0.188	0.391	0.340	0.474	0.340	0.474
Speed limit (1 if 40 mph, 0 otherwise)	0.137	0.344	0.117	0.322	0.141	0.349	0.141	0.349
Speed limit (1 if 50 mph, 0 otherwise)	0.069	0.253	0.059	0.235	0.089	0.285	0.089	0.285
Speed limit (1 if 60 mph, 0 otherwise)	0.232	0.422	0.289	0.454	0.305	0.460	0.305	0.460
Speed limit (1 if 70 mph, 0 otherwise)	0.063	0.242	0.326	0.469	0.112	0.315	0.112	0.315
Light conditions (1 if daylight, 0 otherwise)	0.703	0.457	0.803	0.398	0.772	0.419	0.772	0.419
Light conditions (1 if darkness-lights lit, 0 otherwise)	0.207	0.405	0.082	0.275	0.117	0.322	0.117	0.322
Light conditions (1 if darkness-lights unlit, 0 otherwise)	0.006	0.075	0.003	0.054	0.004	0.061	0.004	0.061
Light conditions (1 if darkness-no lighting, 0 otherwise)	0.074	0.262	0.097	0.296	0.091	0.288	0.091	0.288
Light conditions (1 if darkness-unknown, 0 otherwise)	0.011	0.103	0.015	0.120	0.016	0.124	0.016	0.124
Weather conditions (1 if fine, 0 otherwise)	0.797	0.402	0.838	0.368	0.828	0.378	0.828	0.378
Weather conditions (1 if raining, 0 otherwise)	0.174	0.380	0.138	0.345	0.138	0.345	0.138	0.345
Weather conditions (1 if snowing, 0 otherwise)	0.003	0.057	0.009	0.094	0.004	0.067	0.004	0.067
Weather conditions (1 if fog or mist, 0 otherwise)	0.005	0.069	0.012	0.108	0.009	0.094	0.009	0.094
Weather conditions (1 if other, 0 otherwise)	0.020	0.140	0.003	0.054	0.021	0.144	0.021	0.144
Road surface (1 if dry, 0 otherwise)	0.627	0.484	0.698	0.460	0.660	0.474	0.660	0.474
Road surface (1 if wet or damp, 0 otherwise)	0.353	0.478	0.285	0.452	0.319	0.466	0.319	0.466
Road surface (1 if snow, 0 otherwise)	0.002	0.045	0.006	0.076	0.003	0.058	0.003	0.058
Road surface (1 if frost or ice, 0 otherwise)	0.013	0.114	0.009	0.094	0.016	0.127	0.016	0.127
Road surface (1 if flood over 3 cm deep, 0 otherwise)	0.004	0.065	0.003	0.054	0.001	0.038	0.001	0.038
Urban area (1 if urban, 0 otherwise)	0.504	0.500	0.223	0.417	0.343	0.475	0.343	0.475
Rural area (1 if rural, 0 otherwise)	0.494	0.500	0.777	0.417	0.657	0.475	0.657	0.475
Vehicle maneuver (1 if reversing, 0 otherwise)	0.003	0.057	0.003	0.054	0.002	0.043	0.004	0.067
Vehicle maneuver (1 if parked, 0 otherwise)	0.007	0.083	0.040	0.195	0.011	0.105	0.024	0.153
Vehicle maneuver (1 if waiting to go, 0 otherwise)	0.022	0.147	0.047	0.212	0.027	0.161	0.029	0.169
Vehicle maneuver (1 if slowing or stopping, 0 otherwise)	0.039	0.193	0.103	0.304	0.049	0.216	0.048	0.214
Vehicle maneuver (1 if moving off, 0 otherwise)	0.038	0.192	0.023	0.152	0.041	0.198	0.026	0.158
Vehicle maneuver (1 if turning, 0 otherwise)	0.194	0.395	0.078	0.268	0.152	0.359	0.153	0.360
Vehicle maneuver (1 if changing lane, 0 otherwise)	0.013	0.115	0.019	0.137	0.015	0.121	0.012	0.110
Vehicle maneuver (1 if overtaking, 0 otherwise)	0.024	0.154	0.019	0.137	0.037	0.190	0.018	0.132
Vehicle maneuver (1 if going ahead other, 0 otherwise)	0.659	0.474	0.668	0.471	0.666	0.472	0.685	0.465
First point of impact (1 if did not impact, 0 otherwise)	0.010	0.102	0.015	0.120	0.013	0.115	0.007	0.081
First point of impact (1 if front, 0 otherwise)	0.651	0.477	0.580	0.494	0.625	0.484	0.639	0.481
First point of impact (1 if back, 0 otherwise)	0.096	0.294	0.236	0.425	0.131	0.338	0.128	0.334
First point of impact (1 if offside, 0 otherwise)	0.158	0.365	0.115	0.319	0.146	0.353	0.152	0.359
First point of impact (1 if nearside, 0 otherwise)	0.085	0.278	0.054	0.227	0.084	0.277	0.075	0.264
Age of vehicle (1 if data missing, 0 otherwise)	0.096	0.294	0.160	0.367	0.085	0.279	0.143	0.350
Age of vehicle (1 if below three years, 0 otherwise)	0.151	0.359	0.241	0.428	0.165	0.371	0.280	0.449
Age of vehicle (1 if 3–10 years, 0 otherwise)	0.451	0.498	0.465	0.499	0.427	0.495	0.410	0.492
Age of vehicle (1 if above ten years, 0 otherwise)	0.301	0.459	0.134	0.341	0.323	0.468	0.167	0.373
Sex of driver (1 if male, 0 otherwise)	0.575	0.494	0.975	0.156	0.601	0.490	0.931	0.253
Sex of driver (1 if female, 0 otherwise)	0.425	0.494	0.025	0.156	0.399	0.490	0.069	0.253
Age band of driver (1 if below 25 years, 0 otherwise)	0.204	0.403	0.084	0.277	0.187	0.390	0.111	0.314
Age band of driver (1 if 26–45 years, 0 otherwise)	0.403	0.491	0.461	0.499	0.412	0.492	0.485	0.500
Age band of driver (1 if 46–65 years, 0 otherwise)	0.271	0.445	0.411	0.492	0.273	0.446	0.363	0.481
Age band of driver (1 if above 65 years, 0 otherwise)	0.123	0.328	0.044	0.205	0.128	0.334	0.041	0.199
Driver home area type (1 if data missing, 0 otherwise)	0.079	0.269	0.132	0.339	0.089	0.284	0.097	0.297
Driver home area type (1 if urban area, 0 otherwise)	0.683	0.465	0.646	0.479	0.610	0.488	0.667	0.471
Driver home area type (1 if small town, 0 otherwise)	0.100	0.299	0.109	0.311	0.125	0.331	0.100	0.300
Driver home area type (1 if rural, 0 otherwise)	0.138	0.345	0.113	0.317	0.176	0.381	0.136	0.343
Month (1 if spring, 0 otherwise)	0.236	0.425	0.213	0.410	0.214	0.410	0.214	0.410
Month (1 if summer, 0 otherwise)	0.249	0.433	0.267	0.443	0.257	0.437	0.257	0.437
Month (1 if autumn, 0 otherwise)	0.270	0.444	0.279	0.449	0.269	0.443	0.269	0.443
Month (1 if winter, 0 otherwise)	0.245	0.430	0.241	0.428	0.261	0.439	0.261	0.439
Crash time (1 if off-peak time, 0 otherwise)	0.632	0.482	0.681	0.466	0.611	0.488	0.611	0.488
Crash time (1 if morning peak, 0 otherwise)	0.165	0.371	0.213	0.410	0.230	0.421	0.230	0.421
Crash time (1 if evening peak, 0 otherwise)	0.203	0.402	0.106	0.308	0.159	0.366	0.159	0.366