The article mentions two car household etc but the actual data comes from the national census where people simply report how much they spend on transportation.

The article mentions two car household etc but the actual data comes from the national census where people simply report how much they spend on transportation. There's no assumptions made about what people's commutes are or what their transportation mode is. People just spend more on transport in the suburbs. The reason is for this is because many of these suburbs are wholly designed for the car and that's the only viable transportation option for anything and the car is the most expensive form of transportation.