Development of Accident Frequency Models with Random Parameters on Interstate Roadway Segments with and without Lighting Systems

Table 5

Average marginal effects and elasticities for random parameters negative binomial models.

	Segments with lighting systems		Segments without lighting systems
	Marginal effect	Elasticity	Marginal effect	Elasticity
Logarithm of averaged daily traffic volume	11.672	1.305	5.24	0.076
Logarithm of segment length	6.743	0.075	4.51	0.042
Proportion of segments with low number of lanes	3.677	0.094	2.79	0.011
Proportion of segments with standard number of lanes	2.871	0.321	2.275	0.4162
Proportion of segments with low left shoulder width	0.356	0.039	0.74	0.035
Proportion of segments with standard left shoulder width	−0.182	−0.02	−0.47	−0.085
Proportion of segments with low right shoulder width	n.a.	n.a.	0.73	0.043
Proportion of segments with standard right shoulder width	−0.291	−0.032	−0.43	−0.059
Proportion of segments with high right shoulder width	n.a.	n.a.	−0.31	−0.057
Number of horizontal curves in segments	0.580	0.116	0.17	0.076
Number of vertical curves in segments	0.420	0.048	0.10	0.017

n.a.: not applicable.