Evaluating the effects of context and scale on individual accessibility: A multilevel approach.

摘要

The intraurban accessibility of individuals is an important topic, but the relationships between accessibility and urban form have not been fully addressed. Conventional proximity-based accessibility measures and prevailing models of urban form treat accessibility as a function of distance and do not allow for any variations in the population. The use of space-time accessibility measures overcomes these limitations by allowing individual's daily travel and activity patterns, as well as personal characteristics, to define their accessibility. But there is also strong reason to believe that place-specific characteristics are important to accessibility by mediating people's access to transportation and services. These influences can be expected to vary by time of day due to congestion as well as limited nighttime business hours. Because of the difficulty of distinguishing contextual effects from socioeconomic variations with conventional methods, the mediating influence of location among areas and at different scales has been evaluated m Portland, Oregon using multilevel modeling techniques. This method allows the isolation of accessibility variations resulting from population differences from those resulting from differences between areas.; The results show that while distance to some urban centers is of importance in explaining variations in individual accessibility, the Portland CBD is only one such center. Household time constraints related to the number of hours worked per week and household size are also important. Time is also important to accessibility because the effects of reductions in accessibility due to congestion and limited business hours are not distributed evenly throughout the metropolitan area. These relationships were examined across a range of spatial scales within Portland, but no significant scale variations in accessibility relationships were found. While the characteristics of neighborhoods provide some explanation for observed variations, individual and household characteristics again provide more consistent explanations for accessibility within Portland. These results are in contrast with common expectations about accessibility and urban form, leading to the conclusions that many statements about cities are of limited usefulness in describing or explaining accessibility patterns.