Densities of Development

 The United States has a population density of approximately 100 persons/sq.mi, obviously far too low to support rail transit. Yet there are numerous rail transit systems in the U.S., many of them carrying high volumes of passengers. It is obvious that the overall average figure 100 is irrelevant to the question of rail transit viability in the U.S.

Similarly, Sonoma County has an overall density of 290 persons/sq.mi. Although nearly three times the density of the U.S., it wouldn't be enough to support rail transit. Likewise, that number is also irrelevant.

If we look at the densities at which people actually live, and calculate the average of those densities, we have a (population weighted) density of 4200 persons per square mile (about the overall density of Sebastopol, and about 15% higher than the overall density of Santa Rosa).

159,000 people reside within a mile of a station in Marin or Sonoma. The total land area within those 14 one mile radius circles is 43 sq.mi., so the average density is 3700 ppsm. Suppose the next 100,000 immigrants to Sonoma or Marin move into those circles. The densities would rise by 2336 ppsm, so the average station area density would become 6036 ppsm.

As a comparison, the population density in the one mile radius around the Redwood City Caltrain station shown on the Transit Villages page is 10,300 ppsm. The density of the west end neighborhood next to Railroad Square in Santa Rosa is about the same, at 10,370 ppsm. But it is only 0.1 sq.mi. in area, a tiny part of the one mile radius circle, much of which is taken up by freeway, the rail ROW, a creek and other non-housing land uses.

3700 ppsm is a very low density for train service, so it must be assumed that most people using the train initially won't be walking to it (this was the assumption used by Schiermeyer in his forecast). As density builds in the station areas, additional ridership can come from walking access.

Densities (persons per square mile) for SMART station areas are shown in the table below, for one mile and half mile radius circles, and for the cities in which they are located.

10/21/04