Determining Causal Factors of Severe Crashes on the Fort Peck Indian Reservation, Montana

Table 1

Initial variables and their frequency and percentage.

		All Roads		IRR⁎		County		State Highways
Variables	Categories	Freq		Freq		Freq		Freq
Response variables
Crash Severity	Fatal +Injury	388	41.28	101	72.14	50	19.38	229	44.81
	PDO	552	58.72	39	27.86	108	41.86	282	55.19
Temporal Characteristics
Day of Week	Weekend	281	29.8	49	35.00	77	29.84	146	28.57
	Weekday	659	70.1	91	65.00	181	70.16	365	71.43
Geometric Characteristics
Alignment	Curve	90	9.57	33	23.57	9	3.49	47	9.20
	Straight	850	90.43	107	76.43	249	96.51	464	90.80
Profile	Grade	155	16.49	32	22.86	25	9.69	94	18.40
	Level	785	83.51	108	77.14	233	90.31	417	81.60
Environmental Factor
Weather Condition	Clear	623	66.28	83	59.29	189	73.26	327	63.99
	Not Clear	317	33.72	57	40.71	69	26.74	184	36.01
Lighting Condition	Daylight	707	75.21	83	59.29	235	91.09	362	70.84
	Dark	233	24.79	57	40.71	23	8.91	149	29.16
Driver Characteristics
Impaired Driving	Yes	252	26.81	64	45.71	46	17.83	135	26.42
	No	688	73.19	76	54.29	212	82.17	376	73.58
First Harmful Events
Overturn/Rollover	140	14.89	58	41.43	2		0.78	77	15.07
Collision with Motor vehicles	508	54.04	26	18.57	212		82.17	250	48.92
Collision with a Ditch/ Embankment	63	6.70	23	16.43	1		0.39	36	7.05
Collision with an Animal	56	5.96	1	0.71	0		0.00	53	10.37
Collision with Pedestrians	23	2.45	2	1.43	7		2.71	12	2.35
Collision with other fixed objects	106	11.28	18	12.86	28		10.85	57	11.15
Others	44	4.68	12	8.57	8		3.10	26	5.09
Roadway Characteristics
Presence of intersection	Intersection	264	28.09	21	15.00	84	32.56	155	30.33
	No intersection	676	71.91	119	85.00	174	67.44	356	69.67
Traffic controls system	Traffic control	665	70.74	106	75.71	186	72.09	347	67.91
	No traffic control	275	29.26	34	24.29	72	27.91	164	32.09
IRR= Indian Reservation Roads
PDO= Property Damage Only crashes