"Workers per car, truck, or van" is the derived measure used to indicate carpooling or vehicle efficiency. It is calculated by dividing the total number of workers who reported using a "car, truck, or van" by the number of "Total vehicles used." The values of number of vehicles for individual workers (DRIVESP) are derived from the JWRIP (ridership variable) as follows:

IF JWRIP = 1 (Drove alone) THEN DRIVESP = 1.000 vehicles;
ELSE IF JWRIP = 2 (In a 2-person carpool) then DRIVESP = 0.500 vehicles;
ELSE IF JWRIP = 3 (In a 3-person carpool) THEN DRIVESP = 0.333 vehicles;
ELSE IF JWRIP = 4 (In a 4-person carpool) THEN DRIVESP = 0.250 vehicles;
ELSE IF JWRIP = 5 or 6 (In a 5- or 6- person carpool) THEN DRIVESP = 0.200 vehicles;
ELSE IF JWRIP = 7 - 10 (In a 7-or-more person carpool) THEN DRIVESP = 0.143 vehicles;
ELSE DRIVESP = blank (nonworker or worker who does not drive to work).

The sum of DRIVESP is the estimated number of "Total vehicles used" by those workers who used a "car, truck, or van." Thus, "workers per car, truck or van" is the sum of all workers who reported using a "car, truck, or van" (JWTR = 1) divided by the sum of DRIVESP for all such workers.