Michael A. Niedzielski

A Spatially Disaggregated Approach to Commuting Efficiency

During the past two decades, the concept of commuting efficiency has been used to evaluate the relationships between the journey to work and land use at the regional scale. The common approach of calculating regional statistics masks the intraurban variation of commuting efficiency. This paper develops an alternative approach to commuting efficiency and spatial structure assessments based on spatial disaggregation. The extension of existing regional measures by estimating zonal average trip lengths for workers leaving home and employers attracting workers facilitates analysis of intrametropolitan commuting efficiency. Spatially disaggregated metrics are formulated and applied to journey-to-work data for the cities of Warsaw, Poznan, Lodz and Krakow in Poland. At the regional scale, excess commuting varies from 48 per cent (Warsaw) to 67 per cent (Lodz). Intraurban variations in excess commuting indicate that estimates of commuting efficiency are impacted by the jobs-housing balance and are sensitive to locations of zones within the study area.

Spatial interaction models from Irish commuting data: variations in trip length by occupation and gender

Core and peripheral contrasts in journey-to-work trip length can be interpreted as imputing the relative value of origin and destination accessibility (yielding theoretical proxies for rent and wages). Because the main variables are shown to be critically dependent on spatial structure, they may be interpreted as showing the shadow prices due to comparative location. There is also a unifying connection between these results and the existing literature on many dimensions: rent gradients, accessibility, and emissivity. In an empirical example, the advantages of a panoramic view of national commuting statistics are shown, using an Irish data set. Variations in the rates of participation in trip making by location, occupation, and gender are examined. Places that emit more trips than would be expected from their relative location are identified. Further, examining ways in which such emissivity is sensitive to a change in trip length highlights the regions where trips could possibly be adjusted to produce a shorter average trip length or which might be especially sensitive to reduction in employment. A careful reinterpretation of one of the key outputs from a calibrated spatial interaction model is shown to be consistent with the declining rent gradient expected from Alonso’s theory of land use.

Are Long Commute Distances Inefficient and Disorderly

By joining ideas from the spatial interaction and excess commuting literatures, we integrate and organize three related aspects of commuting statistics: trip length, distance decay, and entropy. We use concepts and calculations from the excess commuting literature to improve interpretation of trip length parameters in a doubly constrained trip distribution model. We derive a direct mathematical relationship between trip length and entropy, thereby providing an analytical model to calculate the ease with which trip lengths might be reduced. The new analysis not only ties these statistics together in a mathematically useful way, but also allows for a new entropy metric—relative entropy—that determines the organization (or lack thereof) of aggregate work trips. As a result, we disentangle the entropy component from the distance component and offer new perspectives on aggregate commuting in a comparative framework. Twenty-five cities are classified in an interesting and useful way that includes the average trip length and the degree of organization in each city.

Travel Time and Distance as Relative Accessibility in the Journey to Work

The ability to access places of opportunity is dependent on the land use distribution, the transportation network connecting homes and activity sites, and sociodemographic-dependent mobility. Accessibility indicators are used as a planning tool to capture accessibility variations in the assessment and development of social, land use, and transportation policy. A number of metrics have been proposed to understand patterns of unequal access that typically fall under overlapping three pairs of contrasting notions of accessibility: place- versus person-based, normative versus positive, and potential versus actual. Variations in accessibility for different people in different locations might arise from the dynamic nature of the people–space–transportation triad. What is less explored is how these dynamics, resulting from the confluence of changing urban structures, diverging mobility resources, and socioeconomic transformations, might reveal unusual accessibility experiences based on unexpected travel time and distance relations. Quite simply, longer (shorter) distances can be traversed in shorter (longer) travel times than would be expected given a specific people–space–transportation situation. Using this linear and nonlinear perspective on time–distance relations, we define a new pair of contrasting notions: monotonic versus nonmonotonic accessibility to investigate diverging commuting experiences. We demonstrate this idea by performing a place-based analysis of commuting data disaggregated by poverty status in the Denver metropolitan area. We find that (1) unexpected commuting experiences do exist and constitute a signification portion of commutes; (2) accessibility variations that are generally not anticipated by traditional place-based metrics; and (3) expected and inverted commuting experiences exist adjacent to each other.

Making Tracks: Rail Networks in World Cities

Urban rail networks are a critical component of successful cities able to compete at a global level in the twenty-first century. They enhance a citys economic efficiency, quality of life, and image through their traditional role as provider of local mobility between home, work, and leisure, as well as their new role in supporting global mobility between airports, business districts, and other critical economic nodes as a strategy to attract highly mobile high-human-capital individuals, investment, and tourists. Using a database of 140 urban rail transit systems at five intervals since 1970, we rank cities using an index that tracks each systems level of population exposure as well as its provision of airport access. We find that (1) higher ranked producer service cities provide better quality local and global mobility; (2) investment in urban rail has dramatically shifted to Asia and that continents megacities are poised to become leaders in providing high levels of local and global mobility; and (3) some developing world cities neglected in the world cities literature have invested in global over local mobility.

Synthesizing spatial interaction data for social science research: Validation and an investigation of spatial mismatch in Wichita, Kansas

Abstract Rising economic segregation suggests a need to examine constraints to job access by race/ethnicity and economic inequality simultaneously. This often requires detailed socio-spatial interaction data to make progress on theoretical and modeling development, empirical studies and policy insights. Commuting data are commonly used because of its wide availability. Despite excellent work trip datasets from the U.S. Census such as the Census Transportation Planning Package and the Longitudinal Employer-Household Dynamics (LEHD) data, there are often gaps between the data that are available and ideal detailed commuting data suited to models and data analysis. This is because commuting data are available for a limited set of socio-economic dimensions and this coarseness limits researchers in their ability to uncover nuances of place-based generalizations about commuting, either socially or spatially. In one promising approach, an information minimizing technique was proposed as a workable practical method to synthesize disaggregated work trip flows. Because the strength of fit between predicted and observed trips is unknown, this paper validates this method using real commutes disaggregated by income and then synthesizes race–income work trips using LEHD data for the Wichita, Kansas metropolitan statistical area. We find that low-income Whites travel longer distances and have more dispersed travel patterns than all African-American and Asian income groups and that both low- and middle-income groups of all race groups have spatially constrained flows.

Investigating Groundwater Vulnerability of a Karst Aquifer in Tampa Bay, Florida

The Floridan aquifer system (FAS) is known to be one of the most productive aquifer systems in the USA. With the FAS being a karst aquifer, it presents unique challenges to land-use planners because of inherent vulnerabilities to contamination through direct connections between the aquifer and the surface. In this study, a new geographic information systems (GISs)-based index, the Karst Aquifer Vulnerability Index (KAVI), incorporates geologic layers used in intrinsic groundwater vulnerability models (GVMs) plus an epikarst layer specific to karst, with land-use coverages to create a specific groundwater vulnerability model. The KAVI model was compared to another specific vulnerability model, the Susceptibility Index (SI). Tabulation of the percentage areas of vulnerability classes reveals major differences between the two models with SI suggesting greater vulnerability for the study area than KAVI. Validation of these two models found that KAVI vulnerability levels best reproduced spatially varying concentrations of nitrate, orthophosphate, and arsenic in the aquifer. Sensitivity analysis, the application of a variation index, and measuring the effective weights for each parameter included in KAVI confirmed the importance of epikarst but also aquifer hydraulic conductivity. The inclusion of land use was justified; however, effective weight analysis determined its assigned weight was too high as used in the initial calculation of KAVI.

Groundwater vulnerability mapping for a sub-catchment of the Rio La Venta watershed, Chiapas, Mexico

Karst systems are particularly vulnerable to overexploitation and pollution due to their high hydraulic conductivity and points of rapid infiltration that allow quick influx of runoff and pollutants into the aquifer. The sustainability of non-contaminated groundwater in these systems is imperative for both humans and groundwater-dependent ecosystems. An important practice in managing groundwater sustainability involves assessing aquifer vulnerability. This study created the first groundwater vulnerability map (GVM) for a sub-catchment of the Rio La Venta watershed in Chiapas, Mexico, using an adaptation of the hazard–pathway–target method. This project also conducted the first tracer study in the Rio la Venta watershed to establish connectivity between the catchment and the Rio La Venta Canyon. Finally, this study evaluated the results of the GVM through a sensitivity analysis. Results of the GVM clearly demarcate areas of very high, high, moderate, and low vulnerability within the study area most of which being classified as low vulnerability. The zones of high vulnerability were successfully validated through two dye tracer tests that measured rapid groundwater flow velocities. With the limited resources available to land managers in this area, a problem common in many developing countries, tools that quickly and inexpensively highlight areas that require special protection to help maintain or improve water quality in their watersheds have great utility. Conveying this information to land managers and policymakers can lead to potential changes in current land use practices and allow for the reallocation of resources in support of reducing future negative human–landscape interactions.