Bayesian Hierarchical Modeling Monthly Crash Counts on Freeway Segments with Temporal Correlation

Table 2

Descriptive statistics of variables in the model.

Variables	Description	Mean	SD	Min.	Max.
Response variable
Crash	Crash count per segment per month	0.372	0.672	0	5
Exposure variables
Length	Segment length (m)	813	303	154.4	2000
MTT	Monthly total traffic (10^3 pcu)	1851	513	1327	3759
Risk factors
	The percentages of vehicles of Category vehicles accounted for (reference case)	38.1	5.76	31.4	53.5
	The percentages of vehicles of Category vehicles accounted for	2.56	0.513	1.97	5.33
	The percentages of vehicles of Category vehicles accounted for	21.9	2.15	15.7	25.5
	The percentages of vehicles of Category vehicles accounted for	6.59	0.766	4.57	7.80
	The percentages of vehicles of Category vehicles accounted for	30.9	5.57	20.2	39.4
Curvature	Segment curvature (0.1 km^−1)	1.77	1.27	0	4.35
Gradient	Segment gradient (%)	0.741	0.568	0	2.91
Bridge	A part of a bridge: yes = 1, no = 0	0.500	0.502	0	1
Access	Presence of roadway access: yes = 1, no = 0	0.210	0.407	0	1

pcu: passenger car units.