Many Transit-Oriented Development guidelines set goals to achieve a certain level of population density. It is intuitive that more residents around a station will lead to more ridership. Cervero and Guerra (2011) investigated the relationship between transit and urban densities in the United States, and found that stations areas need 30-45 people per gross acre within 1/4 mile of a stop in order to put a rail station in the top one-quarter of the most cost-effective investments. When jobs are concentrated within 1/4 mile of a station, and housing within 1/2 mile, ridership gains can be significant.
Population for the blocks within 1/2 mile of each station were calculated using data from the 2010 US Census (people per 1/2 mile of the BART station). Population density was extrapolated, and compared to both single occupancy vehicle (SOV) mode share and Active Transportation mode share (defined as walking, biking, or riding public transit). Population Density is a strong predictor of active transportation with an R-squared of 0.59 and a strong predictor of single-occupancy mode share, with an R-squared of 0.58.