Mass transit in the form of light rail is, in many ways, a new and revolutionary idea for the Greater Los Angeles Area. Although mass light rail transit did exist in Los Angeles in the form of the Pacific Electric Railways red car system, an extensive network of metro rail lines has never existed in Los Angeles County since Pacific Electric was dismantled and shut down in 1950. Because of this, the popular mode of transport in LA County has traditionally been cars, and public transport has consisted mostly of bus routes. This has all changed in the last few decades. Since the 1980s, LA County has conducted several studies and, as a result of those studies, has proposed to build an extensive network of light rail lines to connect the county. In more recent years, many of these project plans have been approved, and the MTA has overseen the construction and functioning of new railway lines that are connecting far-flung regions of LA County with Union Station in downtown LA. Currently, the MTA operates 5 light rail lines within LA county-the Blue Line, the Red Line, the Purple Line, the Green Line and the Gold Line-that extend north, south and east of downtown LA. Each of these lines has been functional for a varying amount of time, but current weekday ridership on this system of lines has crossed the 280,000 mark as off September 2009.

The study examines the relationship between accessibility to public rail transit stations and population growth. Accessibility is measured in time, as in how long it takes to walk to a rail station. The study uses service areas created in a GIS based on how far a person can walk in 10 minutes, comparing the average population growth within these service areas to the average population growth outside of them. Different types of rail transit modes are compared to each other to see if they have differing effects on population growth as well as if multimodal stations affect population growth differently. The results show that accessibility to public rail transit has a positive effect on population growth and that different types of rail transit affect population growth differently. Multimodal stops also have a positive effect on population growth with more transit options resulting in a higher population growth.