An examination of American Community Survey (ACS) data in the major metropolitan areas of the United States shows that suburbs and exurbs have the shortest one-way work trip travel times for the largest number of people. The analysis covers metropolitan areas with more than 1,000,000 population in 2012, from the 2010-2014 ACS (2012 average data) using the City Sector Model.
The City Sector Model
The City Sector Model classifies small areas (zip codes) of major metropolitan areas by their urban function (lifestyle). The City Sector Model includes five sectors (Figure 1). The first two are labeled as “urban core,” (Urban Core: CBD and Urban Core: Ring) replicating the urban densities and travel patterns of pre-World War II US cities, although these likely fall short of densities and travel behavior changes sought by contemporary urban planning (such as Plan Bay Area). There are two suburban sectors, the Earlier Suburbs and Later Suburbs. The fifth sector is the Exurbs, which is outside the built-up urban area. The principle purpose of the City Sector Model is to categorize metropolitan neighborhoods based on their intensity of urbanization, regardless of whether they are located within or outside the boundaries of the historical core municipality (Note 1).
One Way Commute Times by Urban Sector
The commuting data excludes employees who work at home, whose commute times would be zero.
The shortest one-way commute times are experienced by residents of the Earlier Suburbs, with a 26.6 minute travel time. This is nearly equalled for residents of the central business districts (Urban Core: CBD), with an average commute of 26.7 minutes. Commuters living in the Later Suburbs had a somewhat longer commute, at 28.0 minutes, while commuters living in the Exurbs had an average one-way commute of 29.5 minutes. The longest commute times were experienced by residents of the Urban Core: Ring (32.5 minutes), which is the part of the urban core that excludes the central business district, (Figure 2) and is characterized by high densities and lower levels of automobile use than in the suburbs and exurbs.
The functional city sectors with the shortest commutes had more jobs than resident workers. The Earlier Suburbs possess 1.08 jobs for every resident worker (Note 2). The ratio was much higher in the Urban Core: CBD, where there were nearly 5.99 jobs for every resident worker. Such an imbalance could not be replicated throughout a metropolitan area, because by definition, a labor market has a ratio of jobs to resident workers of approximately 1.00. To replicate the national CBD ratio throughout the metropolitan area would require, for example, that the New York metropolitan area have 54 million jobs for its 9 million workers.
Not surprisingly, with such a surplus jobs relative to workers, the Urban Core: CBD, the chances of finding suitable employment nearby is far greater. However, this advantage can, by definition, be available only to a very few, as is indicated by the fact that the Urban Core: CBD's are home to only 1.5 percent of the resident workers in the major metropolitan areas. In the broader context of the urban core (including both the CBD and the Ring), this advantage is offset and average travel times are greater (below).
In the Later Suburbs, there were 0.90 jobs per resident worker, which matches that sector's ranking in work trip travel time (third). The ring around the urban core (Urban Core: Ring) , had the longest average work trip travel time. The Exurbs had the lowest ratio of jobs to resident workers, at 0.71, yet had an average travel time that was shorter than that of the Urban Core: Ring (Figure 3).
Pre-World War II and Post-War Urban Form
The two combined urban core sectors are defined in the City Sector Model to replicate what remains of the pre-World War II city that was characterized by far higher densities and less reliance on automobile transportation, as opposed to the suburban and exurban sectors that have dominated urban growth for seven decades. If the two urban core sectors are combined (Urban Core: CBD and Urban Core: Ring), the number of jobs per resident worker is 1.28. This healthy ratio, however, is not sufficient to preserve any travel time advantage for residents of the combined urban core. In the combined urban core sectors, the average one-way travel time of 31.9 minutes, well above each of the other three functional sectors (Figures 4 and 5). The Urban Core: Ring has nearly nine times as many resident workers as the Urban Core: CBD.
The Pre-War urban form has considerably higher population densities than those of the post-war urban form. For example, the Urban Core: CBD has a population density exceeding 23,000 per square mile (9,000 per square kilometer), more than 80 percent of the New York City population density level. The Urban Core: Ring has a population density exceeding 11,000 per square mile. The combined area population density of the two Urban Core sectors is 11,500 per square mile, or 4,400 per square kilometer (Figure 6).
The two Urban Core sectors largely rely on commuting modes currently favored by urban planning policy, transit, cycling and walking. In contrast, the suburban and exurban sectors rely on commuting modes discouraged by urban planning policy, automobiles and car and van pools (Figure 7).
The combined urban core sectors have more than four times the density of the Earlier Suburbs and nearly nine times the density of the Later Suburbs. With these much higher densities and their reliance on the favored transport strategies, it might be expected that they would enjoy the best commute times. However, as noted above, when the two urban core sectors are combined, their average travel time is longer than the suburban and exurban sectors. This is despite the far lower densities of the two suburban sectors and the often world densities of the exurban sector.
The Key: Lower Densities & Job Dispersion
These results are likely to be surprising to many in the press as well as planners who often equate residential distance from central business districts as resulting in longer commutes. The reality, however, is that central business districts account for only 8 percent of employment in major US metropolitan areas, and reach the highest at 22 percent in New York, 50 percent above second place San Francisco (14.4 percent) and nearly 10 times that of Los Angeles (2.4 percent).
Generally speaking, employment is dispersed throughout the metropolitan area. When combined with the generally lower density urbanization within metropolitan areas, the result is shorter commutes for residents in the suburbs and exurbs. As it turns out the data shows that higher employment densities in the urban core are associated with longer, not shorter commutes, as is commonly assumed.
Note 1: In some cases the functional urban core extends beyond the boundaries of the historical core municipality (such as in New York and Boston). In other cases, there is virtually no functional urban core (such as in San Jose or Phoenix). Functional urban cores accounted for 14.7 percent of the major metropolitan area population in 2012. By comparison, the jurisdictional urban cores (historical core municipalities) had 26.6 percent of the major metropolitan population, many of which have large tracts of functional suburban development.
Note 2: Estimated by dividing the percentage of jobs in each sector by the percentage of resident workers. Working at home is excluded.
Wendell Cox is principal of Demographia, an international pubilc policy and demographics firm. He is a Senior Fellow of the Center for Opportunity Urbanism (US), Senior Fellow for Housing Affordability and Municipal Policy for the Frontier Centre for Public Policy (Canada), and a member of the Board of Advisors of the Center for Demographics and Policy at Chapman University (California). He is co-author of the "Demographia International Housing Affordability Survey" and author of "Demographia World Urban Areas" and "War on the Dream: How Anti-Sprawl Policy Threatens the Quality of Life." He was appointed to three terms on the Los Angeles County Transportation Commission, where he served with the leading city and county leadership as the only non-elected member. He served as a visiting professor at the Conservatoire National des Arts et Metiers, a national university in Paris.
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