Table 1 Definitions of Variables Used

Table 1
Definitions of Variables Used

      Mean* SD*
Dependent variables Annual VMT Annual vehicle-miles traveled in vehicle, as estimated by household respondent. 11,040 8,230
Number of person-trips Number of person-trips in the vehicle on the survey day 7.11 6.2
Number of recreational person-trips Number of person-trips in the vehicle on the survey day for trips of recreational purpose (including social, shopping, and eating-out purposes) 2.2 3.06
Trip occupancy: all purposes Number of vehicle occupants during trip 1.84 1.1
Trip occupancy: recreational purposes Number of vehicle occupants during recreational trip (including social, shopping, and eating-out purposes) 1.71 0.99
Vehicle type chosen for trip Type of vehicle chosen by driver for trip (all purposes included) NA NA
Newest vehicle owned Type of newest-vehicle owned (identified by latest model year); includes passenger car, SUV, pickup, & minivan NA NA
Explanatory variables Population density Population density of census tract (persons per square mile) 3,858 5,306
Income per household member Annual household income (1995 US$) divided by household size (where income is taken to be middle of class range) $19,075 $13,561
Vehicle age 1996 minus model year of vehicle 6.02 4.96
Household members per vehicle owned Household size divided by vehicles owned by household 1.48 0.8
LDT indicator Equals one for SUVs, pickups & minivans (zero otherwise) 0.26 0.44
SUV indicator Equals one for SUVs (zero otherwise) 0.08 0.27
Pickup indicator Equals one for pickups (zero otherwise) 0.11 0.31
Minivan indicator Equals one for minivans (zero otherwise) 0.08 0.27
Vehicle price/income Average purchase price of new vehicle (based on 1997 sales data) divided by annual household income) 0.74 0.14
Household size Number of household members 2.83 1.31
Number of vehicles already owned Number of vehicles already owned by household, of that vehicle type 0.92 0.87
Number of cars already owned Number of passenger cars already owned by household 0.56 0.69
Weekend day Equals one for Saturday and Sunday trips (zero otherwise) 0.22 0.42
Vehicle occupancy Number of vehicle occupants (for model of vehicle-type choice) 1.58 0.99
Trip length Self-reported trip travel time (minutes) 14.21 13

*Note: Means and standard deviations (SDs) vary slightly in some cases, according to sample used/model applied