No abstract

Analytical methods for evaluating accessibility have been based on a spatial logic through which the impedance of distance shapes mobility and urban form through processes of locational and travel decision making. These methods are not suitable for understanding individual experiences because of recent changes in the processes underlying contempora y urbanism and the increasing importance of information and communications technologies (ICTs) in people's daily lives. In this paper we argue that analysis of individual accessibility can no longer ignore the complexities and opportunities brought forth by these changes. Further, we argue that the efsect of distance on the spatial structure of contempora y cities and human spatial behavior has become much more complicated than what has been conceived in conventional urban models and concepts of accessibility. We suggest that the methods and measures formulated around the mid-twentieth centu y are becoming increasingly inadequate for grappling with the complex relationships among urban form, mobility, and individual accessibility. We consider some new possibilities for modeling individual accessibility and their implications for geographical analysis in the twenty$rst centu y.

An important methodological issue in accessibility research is how the results are affected by geographical scale. Understanding the scale effect and the associated modifiable areal unit problem (MAUP) is also important for the analysis of land use-travel interaction. Using a distinct type of accessibility measures, namely space-time measures, this study examines whether the relationships among accessibility, land use, and personal and household characteristics vary systematically with geographical scale. Space-time accessibility measures were implemented using an activity-travel diary data set collected in the Portland (Oregon, USA) metropolitan area. Through multilevel models, the study shows that these relationships are scale invariant.

Although recent studies of individual accessibility have used detailed representations of urban street networks, unrealistic measures of travel time based on assumptions about constant travel speeds through the network were often used. Utilizing constant travel times does not allow for daily congestion and assumes that the effects of congestion are uniform throughout the city and affect all people equally. This research measures individual space-time accessibility in order to show that the incorporation of locally specific travel times within a street network allows a significant increase in the ability to realistically evaluate individual accessibility within cities. The results show that the accessibility of individuals within cities is not homogenous, and neither does access to employment or shopping opportunities vary according to common expectations about urban form and human behavior. Instead, the role of distance in predicting accessibility variations within cities is quite limited. This article also shows that incorporating time into accessibility measures in the form of congestion and business hours leads to additional (and highly spatially uneven) reductions in accessibility, revealing that the temporal dimension is very important to accurately assessing individual accessibility.

Among others, one commonly identified negative consequence of urban sprawl is an increase in the length of the journey to work. However, there has been more discussion of this than serious scrutiny, hence the relationship between urban sprawl and commuting patterns, especially at the intraurban level, remains unclear. Using the 2000 Census Transportation Planning Package (CTPP) data for two Southeastern metropolitan areas, this research investigates the extent to which workers living in sprawl areas commute farther to work than those living in higher density areas. The analysis of variance confirms that workers commuting from sprawl areas to urban areas experience a longer commute in terms of time as well as mileage, though this varies when workplace and home locations are taken into account. However, multivariate statistical results suggest that there are limits to the utility of sprawl as a predictor of travel behavior compared to workers' socioeconomic characteristics, as other factors appear to be equally or more important.