Analysis of Severe Injury Accident Rates on Interstate Highways Using a Random Parameter Tobit Model

Table 1

Descriptive statistics of variables.

Variable description	Mean	Std. dev.	Minimum	Maximum
Number of disabling injury accidents	0.161	0.439	0	5
Number of fatality injury accidents	0.058	0.246	0	2
Segment length (mi)	1.837	2.329	0.010	20.380
Average annual daily traffic volume	13,052	8,426	916	44,224
Number of lanes per direction	2.622	0.735	1	5
Left shoulder width (ft)	6.946	3.217	2	14
Right shoulder width (ft)	6.943	3.280	2	18
Number of horizontal curves	1.817	2.483	0	37
Number of vertical curves	3.183	3.248	0	30