Table 1: Descriptive characteristic for key variables.

VariablesMeanStd. Dev.Min.Max.

The exposure variable (Offset)
 Vehicle miles traveled11.76048.2360.037797.400
Explanatory variables
 Intersection density2.3211.878012.255
 Road segment in rural areas18901
 Road segment in urban areas79401
 Ownership at state or federal levels13901
 Ownership at other levels84401
 Number of through lanes less and equal to 266101
 Number of through lanes greater than 232201
 Not on a designated truck route89301
 Designated truck route9001
 Annual average daily traffic75234053700
 Pavement condition rating2.9970.73715
 Pavement type at low level44201
 Pavement type at high level54101
 Percent average daily trucks2.4002.477117