Public Transit Quality Determined by Population Density

How Does Distance Affect Modal Choice?

Mamon and Marshall's (1977) model, meanwhile, holds the key assumption that the densities at which individuals live and work are proxies for the level and quality of public transportation available to them. They argue that when the residential population is scattered in single family dwelling units, each on its own lot, provision of adequate mass transportation services using traditional technologies is extremely difficult. In particular, when there are no well-defined (high density) collection and dispersal points, vehicles such as buses and trains are inconvenient. This is because most potential passengers must travel long distances from their homes to loading points and from terminal points to their places of employment (Schnore, 1957; Meyer, 1970; Dyckman, 1965; cited in Mamon & Marshall, 1977).

Mammon and Marshall (1977) use residential and employment density as their two structural variables, and they argue that they are an important part of the context within which commuters make their decisions about methods of transportation to work. Specifically, they predict that persons who live and/or work at high densities are more likely to use public transportation than persons who live and work at low densities.

Finally, Mamon and Marshall (1977) anticipate that income affects both employment and residential density. Persons with low income are less likely to be able to afford the single-family dwelling units characteristic of low density residential areas. Regarding employment, however, a substantial proportion of the industrial and clerical work has been dispersed into the low density fringe areas. This suggests that relatively low paid jobs will be found in low density areas, unlike higher paid jobs which are still relatively centralized.

According to these findings, the dispersal of jobs and residences in Los Angeles into low density suburban areas does not bode well for public transportation. In other words, assuming that density adequately reflects quality of service, which the strong influence of Mamons' and Marshalls' (1977) density variables suggests, it will be increasingly difficult to induce people to use public transportation no matter how much money is poured into improving present systems, since increasingly smaller proportions of people will live under the conditions in which it will be used. Mamon and Marshall (1977) feel that simply modernizing public transportation in isolation will not alter present trends significantly.