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