At high densities, land uses get close enough to each other to support walk, bike, and transit modes above 60% of total trips. The San Francisco Bay Area census was used to define five density levels: rural, exurban, suburban, central city, and urban core. The urban core definition, over 50 persons per neighborhood acre, is much denser than in other research. The California Household Transportation Survey supplied new data on block group area, population, trip stages, trip distances, trip time, and travel mode by density. The National Household Transportation Survey supplied block group population, density, travel mode, and income data. Both sources show a strong nonlinear relationship going from rural to urban core: auto miles and trips decrease as walk and transit miles and trips increase. With density, people travel fewer miles and spend less time traveling. High-income households in dense areas travel far fewer miles than those living at higher densities. With sufficient density, complementary features play a role in furthering mode shift. For planning purposes, the need for parking greatly declines. The findings are a basis for similar research elsewhere on high densities and complementary features.

The major US household travel surveys do not ask the right questions to understand mobility in Walkable Neighborhoods. Yet few subjects can be more important for sustainability and real economic growth based on all things of value, including sustainability, affordability, and quality of life. Walkable Neighborhoods are a system of land use, transportation, and transportation pricing. They are areas with attractive walking distances of residential and local business land uses of sufficient density to support enough business and transit, with mobility comparable to suburbia and without owning an auto. Mobility is defined as the travel time typically spent to reach destinations outside the home, not trips among other destinations that are not related to the home base. A home round trip returns home the same day, a way of defining routine trips based on the home location. Trip times and purposes, taken together, constitute travel time budgets and add up to total travel time in the course of a day. Furthermore, for Walkable Neighborhoods, the analysis focuses on the trips most important for daily mobility. Mismeasurement consists of including trips that are not real trips to destinations outside the home, totaling 48 percent of trips. It includes purposes that are not short trips functional for walk times and mixing of different trips into single purposes, resulting in even less useful data. The surveys do not separate home round trips from other major trip types such as work round trips and overnight trips. The major household surveys collect vast amounts of information without insight into the data needed for neighborhood sustainability. The methodology of statistics gets in the way of using statistics for the deeper insights we need. Household travel surveys need to be reframed to provide the information needed to understand and improve Walkable Neighborhoods. This research makes progress on the issue, but mismeasurement prevents a better understanding of the issue.