The City is flatter: Changing patterns of job and labor access
Introduction
The coevolution of transport and land use has been established historically in a variety of contexts (Levinson, 2008, Xie and Levinson, 2009b, Kasraian et al., 2016). But coevolution is not just an historical phenomenon, it is something we see everyday as households and firms relocate to improve their condition in a changing economic landscape, and as transport providers restructure and extend transport networks to better serve their customers. Locators select metropolitan regions to be near activities, things, organizations, and people that are important to them, and they select locations within metropolitan areas for similar reasons, trading off benefits and costs of those locations.
In cities, firms aim to achieve economies of agglomeration and improve productivity and output by locating near customers (other firms and/or households depending on the nature of the firm), suppliers (including their labor force), and even competitors – creating a centripetal force in cities, while trying to reduce costs of land and congestion (which is a centrifugal force). Households aim to achieve proximity to their work, shops, and other activities and amenities (also a centripetal force) while simultaneously obtaining more house and lot for the money, producing a centrifugal force on urban regions. This tension between centripetal and centrifugal forces keeps the city from achieving either a maximal density (all activities on a single point) or a minimal density (all activities spread out evenly across space). However the balance between these two forces changes over time with exogenous changes in other technologies (e.g. vehicles, communication, finance), demographics (e.g. the relative demand for living space varies by life-cycle), socio-economics (e.g. the income or wealth of consumers), and other preferences (e.g. willingness to commute, time scarcity).
The concept of accessibility allows us to measure the efficiency of the city in its primary role, enabling people to reach other people, places, and things. Accessibility is by definition a very complex matter, which also, for example, includes individual capabilities, needs, and wishes, as well as competition. The concept has been well-described in the literature (Handy and Niemeier, 1997, Kwan and Weber, 2003, Geurs and Van Wee, 2004, Scott and Horner, 2008, Ottensmann and Lindsey, 2008, van Wee and Geurs, 2016), and is applied here in a new empirical context.
Accessibility as used here is a concept of potential associated with places, not realized or actual travel conducted by individual persons at a given time. While the two are correlated, the relationship is far from perfect (Niedzielski & Boschmann, 2014). Some European literature discusses the concept of territorial cohesion, which may be formulated as a normative accessibility goal aiming to ensure “citizens have equal access to facilities services and knowledge” (Mirwaldt et al., 2009). We treat accessibility here as a positive rather than a normative concept, we are simply trying to measure the change in opportunities, without passing value judgment or establishing standards (Páez et al., 2012).
This study measures access to jobs and to labor by automobile. It thus differs from previous research in one important aspect, we use measured rather than modeled accessibility. This means the inputs to the maps presented here are the results of direct measurements of travel times and delay (supplemented by carefully calibrated direct travel time models where flows are available and speeds are not) rather than the outputs of a regional transportation planning/forecasting model or based on assumptions of travel speeds based on road classification.
This study further examines the change in the makeup of accessibility in the Minneapolis-Saint Paul, Minnesota (Twin Cities) metropolitan area between 1995 and 2005 and tests whether, playing off the title of Thomas Friedman's book The World is Flat (Friedman, 2007), The City is Flatter than it used to be. Other studies have looked at the evolution of US cities, e.g. (Giuliano et al., 2007) illustrates the emergence of regional subcenters in the Los Angeles area, and (Giuliano et al., 2012) shows that growth depends on accessibility. In contrast, (Helling, 1998) found declining accessibility in Atlanta through the 1980s.
Minneapolis and Saint Paul arose like many cities in the late 19th and early 20th centuries around the streetcar (Xie & Levinson, 2009a), but ultimately adopted the automobile highway system as the primary means of transport (Iacono & Levinson, 2009). This study focuses on auto accessibility, as automobile is the dominant mode of travel for longer trips. Other studies by the authors examine transit accessibility in the region (Owen & Levinson, 2015), and related studies look at access to non-work destinations (Iacono et al., 2010).
The period between 1995 and 2005 saw a number of changes in the Twin Cities. Population and employment rose on the order of 1% annually, the economy went through one recession associated with the Dot Com bubble, decline in the stock market, and 9/11, and toward the end of the period fuel prices began their rise (ultimately peaking (to date) in 2008). However this is also a period of relative stability in the transport network. The Twin Cities Interstate system was essentially complete in 1994, and though roads have widened some and new non-freeway links built, these have been relatively minor. There was a relatively sharp increase in traffic in the first part of this period, before a leveling off in the later years. Between 1995 and 2005 we see a larger increase in growth in both jobs and workers in the suburbs than the central cities of Minneapolis and St. Paul. This notion of the flattening of the city has been measured in various ways, including e.g. land value (Heikkila et al., 1989), travel times (Gordon et al., 1989, Levinson and Kumar, 1994), and analysis of subcenters (McMillen & McDonald, 1998).
The next section describes methodology on accessibility. This is followed by the data used in this study for both land use and travel times. A travel time matrix is developed and applied to determine the cumulative number of jobs or workers accessible in a given time band. The results highlight maps and numeric analyses underlying those maps. We focus on trends from a series of maps within fewer time bands to examine shifts in accessibility more deeply. Specifically, we will look at key commute times including 15, 20, 25, and 30 min commute-time thresholds. Later, we will narrow the focus to accessibility in years 1995 and 2005 at the 20 min commute in an attempt to disentangle those aspects of accessibility associated with different accessibility impacts that may be attributed to land use changes or with changes in the transport system. The paper concludes with implications for policy and the potential for future research in this arena.
Section snippets
Methodology
Taken by itself, the travel time matrix measures mobility. The information it contains, along with the network topology, is enough to determine the speed at which network users can travel from any zone to any other. However, transport is often described as a derived demand, which means that mobility is not an end in itself, but is necessary due to the spatial separation of other activities or objectives (Wachs & Kumagai, 1973). As long as travel is occurring for reasons other than pleasure, the
Data
This study generates accessibility measures that take as inputs a matrix of origin-destination (O-D) travel times for the region that is derived from actual traffic data, rather than relying on modeled zone-to-zone travel times, which are subject to significant definitional problems (Salonen & Toivonen, 2013). To that effect, several sources of traffic count data and link travel time estimates are employed. The components of the travel time matrix include freeway travel time estimates, freeway
Accessibility to jobs and workers
The changes in accessibility from 1995 to 2005 are described in this section. The detailed results are illustrated in Fig. 3, Fig. 4 for accessibility to jobs and to workers by auto within 20 min for 1995 and 2005 for the AM peak period. Other results can be found in (Levinson et al., 2010). It should be noted in all of these maps that the larger TAZ on the maps are those with the smallest population, so that areas that dominate visually are not necessarily those of most practical importance
The
Conclusions
This study describes the process and outcomes resulting from an effort to measure changes in regional accessibility by auto during the period from 1995 to 2005. In contrast to the earlier research efforts that make use of accessibility metrics from travel demand models, this project derives time-dependent measures of accessibility that use as inputs travel time estimates based (to the extent possible) on directly measured travel times or observed link flows. These measures are then tracked over
Acknowledgments
We would like to thank John Hourdos and Ted Morris from the Minnesota Traffic Observatory for their assistance with developing the arterial travel time estimates, and for providing information on the collection of signal timing data to augment arterial link travel times. We would also like to thank Hui Xiong for providing valuable information on the process of updating arterial link counts in the absence of reliable traffic count data. Michael Iacono, Jason Junge, Shu Hong, Pavithra
References (46)
- et al.
Accessibility evaluation of land-use and transport strategies: Review and research directions
Journal of Transport Geography
(2004) - et al.
The influence of metropolitan spatial structure on commuting time
Journal of Urban Economics
(1989) - et al.
Measuring non-motorized accessibility: Issues, alternatives, and execution
Journal of Transport Geography
(2010) Accessibility and the journey to work
Journal of Transport Geography
(1998)- et al.
Suburban subcenters and employment density in metropolitan Chicago
Journal of Urban Economics
(1998) - et al.
Accessibility indicators for transport planning
Transportation Research Part A: General
(1979) - et al.
Modeling the commute mode share of transit using continuous accessibility to jobs
Transportation Research Part A: Policy and Practice
(2015) - et al.
Measuring accessibility: Positive and normative implementations of various accessibility indicators
Journal of Transport Geography
(2012) - et al.
Modelling travel time in urban networks: Comparable measures for private car and public transport
Journal of Transport Geography
(2013) - et al.
Physical accessibility as a social indicator
Socio-economic Planning Science
(1973)
Jobs-housing balancing and regional mobility
Journal of the American Planning Association
Jobs-housing balance revisited: Trends and impacts in the San Francisco Bay Area
Journal of the American Planning Association
Commuting in restructuring urban regions
Urban Studies
Mapping crime: Understanding hotspots. Technical report
Access to destinations: Development of accessibility measures
The world is flat: A brief history of the twenty-first century
Is the journey to work explained by urban structure?
Urban Studies
Employment concentrations in Los Angeles, 1980–2000
Environment and Planning A
Network accessibility and employment centres
Urban Studies
Measuring accessibility: An exploration of issues and alternatives
Environment and planning A
How accessibility shapes land use
Journal of the American Planning Association
What happened to the CBD-distance gradient? Land values in a policentric city
Environment and Planning A
Changing intra-metropolitan accessibility in the US: Evidence from Atlanta
Progress in Planning
Cited by (18)
How has the efficiency of China's green development evolved? An improved non-radial directional distance function measurement
2022, Science of the Total EnvironmentCitation Excerpt :This enables a comprehensive understanding of the spatial distribution characteristics. SDE is an effective way to disclose the distribution pattern of the elements of interest, and has been widely used to statistically analyze spatial patterns (Levinson et al., 2017; Richter et al., 2021; Zhang et al., 2020). SDE can comprehensively describe the distribution of parameters and the evolution of those parameters from the perspective of centrality, spreadability, density, directionality, and shape.
Inequalities in transit accessibility: Contributions from a comparative study between Global South and North metropolitan regions
2021, CitiesCitation Excerpt :Nonetheless comparative research that involves accessibility based on empirical studies in distinct urban contexts is still not so common. Some studies compare the accessibilities of cities within the same country (Levinson et al., 2017; Scheurer et al., 2017) or the same continent (Moya-Gómez & García-Palomares, 2017) but few studies have provided an intercontinental cities comparison. This study investigates inequalities in transit accessibility in areas across the Global South and North.
Revisiting urban sustainability from access to jobs: Assessment of economic gain versus loss of social equity
2020, Environmental Impact Assessment ReviewNetwork structure and the journey to work: An intra-metropolitan analysis
2018, Transportation Research Part A: Policy and Practice