Highway Design and Safety Consequences: A Case Study of Interstate Highway Vertical Grades

Table 1

Descriptive statistics of variables.

	Mean	Std Dev	Minimum	Maximum
Rural Interstate
Total number of fatal crashes on each segment	0.241	0.501	0	3
Total number of injury crashes on each segment	4.265	3.785	0	19
Total number of PDO crashes on each segment	18.030	15.206	0	79
Segment length (miles)	5.417	2.824	0.560	6.94
Average annual daily traffic (10,000 vehicles)	3.271	1.600	1.181	12.865
Lane width (ft.)	12.030	0.784	8.750	15
Right shoulder width (ft.)	10.335	0.981	2.800	12
Pavement roughness (IRI in in/mile)	80.553	29.482	53	219
Vertical curve grade (%)	1.639	1.950	0	4.084
Road segments with left shoulder or median	100%		0	1
Left shoulder width (ft.)	4.562	1.765	3	11
Median width (ft.)	61.236	14.308	2	60
Urban Interstate
Total number of fatal crashes on each segment	0.650	1.336	0	7
Total number of injury crashes on each segment	30	60.224	0	228
Total number of PDO crashes on each segment	121.688	261.035	0	953
Segment length (miles)	5.372	2.868	0.400	6.44
Average annual daily traffic (10,000 vehicles)	5.275	3.298	1.140	12.385
Lane width (ft.)	11.986	0.561	10	14.460
Right shoulder width (ft.)	9.953	0.723	6	11
Pavement roughness (IRI in in/mile)	77.329	21.613	48	147
Vertical curve grade (%)	1.540	1.883	0	3.682
Road segments with left shoulder or median	97.50%		0	1
Left shoulder width (ft.)	5.965	4.182	0	15
Median width (ft.)	45.241	21.637	0	60