TABLE 2 Variable List,
Variable,Description
Tract or zip,U.S. census tracts and five digit zip code tabulation areas (an aggregation of census blocks) were used to define the boundaries for local land-use characteristics 
Driver status,"Driver status of respondent: licensed, not licensed, or not appropriate"
Worker status,"Worker status of respondent: working, nonworking, or not appropriate"
Age,"Age of respondent: 0–5 years, 6–16 years, 17–65 years, 66 years and more"
Vehicle count,Number of vehicles in household: 1–9 or more
Household size,Household size: 1–9 or more
Race,"Race of the head of household: White, African American, Hispanic, other (including Asian)"
Driver count,Number of drivers in household: 1–6 or more
Personal income,"Household income divided by number of persons in household; 11 classes from $0–$100,000 or more"
Transportation mode choice,"Transportation mode choice among motorized options, walking and biking, or transit (including buses, metro, and rail)"
% low residential,"Low-density residential: detached single-family/duplex dwelling units, yards, and associated areas; areas of more than 90% single-family/duplex dwelling units, with lot sizes of less than 5 acres but at least half an acre (0.2 dwelling units/acre to 2 dwelling units/acre)"
% medium residential,"Medium-density residential: detached single-family/duplex, attached single-unit row housing, yards, and associated areas; areas of more than 90% single-family/duplex units and attached single-unit row housing, with lot sizes of less than half an acre but at least one-eighth acre (2 dwelling units/acre to 8 dwelling units/acre)"
% high residential,"High-density residential: attached single-unit row housing, garden apartments, high-rise apartments/condominiums, mobile homes, and trailer parks; areas of more than 90% high-density residential units, with more than 8 dwelling units per acre"
% commercial,"Commercial, retail, and wholesale services; areas used primarily for the sale of products and services, including associated yards and parking areas"
% industrial,"Manufacturing and industrial parks, including associated warehouses, storage yards, research laboratories, and parking areas"
% vacant,"Vacant land, such as bodies of water "
% other,Other land uses
Road density index,"Liner road length over square areas, 10 classes, with a lower value indicating denser road networks"