Semisequicentennial Transportation Conference Proceedings
May 1996, Iowa State University, Ames, Iowa
The Need (and Opportunity) for Comprehensive Land-Use and Transportation Planning
Eric Damian Kelly and Daniel R. Mandelker
Ball State University,
College of Architecture and Planning,
Muncie, Indiana 47306.
Washington University School of Law,
8903 Wrenwood Lane,
St. Louis, Missouri 63144.
This paper compares land-use and transportation issues in Des Moines, Iowa, and Lincoln, Nebraska, state capitals that are located less than 200 miles apart along I-80 and each having a population of about 200,000. Although the cities share many similarities, there are radical differences. Lincoln literally has no suburbs. It is its own urbanized area, and it contains most of the population of the one-county Metropolitan Statistical Area. Des Moines has roughly two dozen suburbs and exurbs, with 17 other incorporated cities in Polk County alone and several others within easy commuting range in Dallas and Warren counties. More important for purposes of this paper, the local traffic patterns on the interstate highways through the two communities are radically different. Commuting traffic on the interstate system through Des Moines roughly triples the traffic load on interstate highways in and near the city, and that load continues to grow. That growth has led to a current proposal for an expansion of the main interstate highway through Des Moines (I-235, locally called the MacVicar Freeway) at a cost of hundreds of millions of dollars. In contrast, traffic counts on I-80 at most points in Lincoln are actually lower than the counts on I-80 at either end of the city. Thus, Lincoln and the Nebraska Department of Roads are not faced with the same sort of costly and disruptive highway proposals that Des Moines and the Iowa Department of Transportation must consider. Although it is difficult to prove causation, the relationship is too strong to ignore, particularly when bolstered by extensive published studies from other communities. Transportation networks clearly influence urban form, but changing urban form also influences transportation patterns.
A Tale of Two Midwestern Cities
This paper compares the urban form and transportation patterns of Des Moines, Iowa, and Lincoln, Nebraska. The cities are similar in many ways. They are both state capitals. Both are midsize cities, Des Moines with a 1990 population of 193,187 and Lincoln with a 1990 population of 191,972. Both are located along Interstate 80, a little less than 200 miles apart.
As shown in Tables 1 and 2, the population patterns of the two areas suggest some of the similarities and the differences.
|TABLE 1 Des Moines Metropolitan Population Trends 1950-90|
aPolk (includes Des Moines), Warren, and Dallas.All data from Bureau of the Census, various years, see note (1).
|TABLE 2 Lincoln Population Trends|
All data from Bureau of the Census, various years, see note (1).
Eighty-nine percent (89%) of the metropolitan population remained in Des Moines, but by 1990, only seventy percent (70%) of the population was in the city, and the city itself continued to experience out-migration. Lincoln provides a significant contrast. The city is literally the metropolitan area. Thus, one hundred percent of the population of the metro area continues to live in the city.
The impact of these trends on urban form has been dramatic. Table 3 shows the trends in land area of the urbanized, or built-up, areas of the two communities.
|TABLE 3 Land Areas, Des Moines and Lincoln Urbanized Areas 1950-90|
What does all that mean? It means that the Des Moines area sprawled, in the most literal sense of the word. Table 4 shows that sprawl in different termsthe number of persons per square mile of urbanized area.
|TABLE 4 Population Densities, Persons Per Square Mile, Des Moines and Lincoln Urbanized Areas, 1950-90|
All data from Bureau of the Census, various years, see note (1).
The difference is not explained by larger families. Occupancy patterns throughout the relevant period are fairly similar, and it is Des Moines, not Lincoln, that has slightly larger household sizes, a fact which would tend to increase the density of population in Des Moines (1). In short, the real difference between the two is not a simple demographic oneit is one that involves land-use and planning. Lincoln is a more densely settled city. There is no evidence that Lincoln has tried to force people onto smaller lots or into denser patterns of living. Rather, it appears that the planning and growth management emphasis of the city has effectively placed a higher relative value on land and on its efficient use. The result is a development pattern that is more efficient from a public services perspective.
Although the differences in density within the urbanized areas are significant indeed, the exurban development is equally significant. In Lancaster County (Lincoln), ten percent (10%) of the population resided outside the city in 1990. In that same year, twenty-three percent (23%) of the metropolitan county population of the Des Moines area lived outside the Metropolitan Statistical Area at that time
In short, the Des Moines metropolitan area is more sprawling than that of Lincoln in two ways. First, the urbanized area itself is less dense. Second, a much higher proportion of people in the metropolitan area counties of the Des Moines area live in the exurban parts of those counties than in the Lincoln area.
Factors Influencing Urban Form
There appear to be three basic factors that explain that sprawl: the pattern of highways; a long-range plan for regional sewage treatment, adopted in 1976; and annexation policies of the City of Des Moines. Clearly the pattern of highwaysforming roughly an east-west oval that included the central part of Des Moines and extended to the west into land that was undeveloped when the oval was builtoffers a significant explanation of the urban form. By 1990, the continuing sprawl to the west had completely filled the western section of the oval, and population continued to expand along major transportation routes outside the oval. The only undeveloped areas remaining within that oval by 1990 are lands with severe flooding and other environmental problems. By the date of completion of this study, actual development has gone well beyond that oval to the west, northwest and southwest, leading to a major upgrading of U.S. 6 to the west, which is likely to facilitate even more western-exurban commuting and development.
It is important to note, however, that this strong urban development pattern was significantly reinforced by the sewer service boundary established in 1976 for the Metro sewer system, which serves the city and most of its suburban areas. The other obvious determinant in the shaping of urban form relates to annexation policies. Some of the differences are historic, going back decades to the creation of forms of government in the states. In Nebraska, primary class cities (which basically means Lincoln) have the authority to annex second-class cities and villages. Thus, Lincoln has had an enforcement tool available to help prevent the evolution of suburbs on its fringes. In Iowa, there is no such power. There are currently 18 municipalities in Polk County, and most of those have existed throughout the period of this study (Johnston, Clive, Pleasant Hill, and Urbandale are relatively new). Thus, part of the destiny of these areas was created by early settlement patterns and early legislative enactments regarding local governments. The cities have also used their annexation powers differently. Lincoln has continually annexed territory to provide for future expansion, while Des Moines tacitly ceded most annexations to its suburbs after about 1960. Although more than sixty-seven percent (67%) of the urbanized area was within the Des Moines city limits in 1960, by 1990 that had shrunk to forty-seven percent (47%).
Although there are many similarities between Lincoln and Des Moines, their transportation patterns are as different asand directly related totheir population and development patterns.
In Lincoln, traffic on I-80 at the eastern edge of the city (84th Street) amounts to 21,300 average daily trips. At the west edge, it totals 23,200 average daily trips. Traffic on most intervening segments is actually lower than either of those figures, indicating that much of the traffic on the road is destination traffic to or from Lincoln, using the interstate highway as exactly thator at least as an inter-city highway. The only segment on which the traffic volumes are higher than at the edges of the city is from Salt Valley Roadway to Cornhusker Highway, where there are 28,300 average daily trips (2). In general, however, traffic in Lincoln is relatively well-distributed around the grid, with major arterials on the grid carrying up to 20,000 trips per day (or more in some instances) and many segments carrying 10,000 or more (2).
The circumstances in Des Moines are quite different. The analysis is also more complex, and Table 5 is useful to understand that.
|TABLE 5 Traffic Loads, Selected Locations on Interstate Highways around Des Moines, Iowa, 1992|
|Interstate location||Average daily trips||Estimated through traffic|
|I-35 at south edge (south limits of West Des Moines)||21,000|
|I-35 at north edge (north limits of Ankeny)||22,100|
|I-80 at west edge (west line of Polk County)||28,100|
|I-80 at east edge (Iowa 945 and Co. Rd S 14)||29,100|
Source: (3)."Estimated through traffic" computed by the author by averaging loads on same road at each end of city.Note on data: This is a gross over-simplification in origin-destination terms, but in straight statistical traffic analysis, it is perfectly valid. At worst, it over-estimates through traffic. Typical traffic loads on I-80 further west are in the 14,000 to 17,000 range, and to the east are fairly consistently in the 21,000 to 22,000 range all the way to the Illinois line. Loads on I-35 further north decrease with distance from Des Moines, dropping below 17,000 past Ames and U.S. 30 and below 12,000 past U.S. 20. Loads on I-35 further south decrease even more rapidly, falling below 12,000 at Indianola and below 9,000 by the Missouri line. Thus, estimating through trips of 50,000 per day is high and clearly includes a number of Des Moines-destination and origin trips in all directions (a fact that is more clearly illustrated with the Lincoln figures). In short, this methodology at worst over states through trips and understates the commuting problem in Des Moines.
Traffic flow into and out of Des Moines both directions on I-35 averages about 21,550 trips per day. Traffic flow into and out of Des Moines both directions on I-80 averages about 28,600 trips per day. These figures give a good idea of the net number of through trips that could be expected without regard to commuting. Obviously this is a macro view of "through trips" rather than an origin-destination analysis of them, because it clearly includes some trips with trip-ends in Des Moines. The point, however, is that, without commuting trips, one would expect the traffic on the interstate highways in Des Moines to be less than or equal to the imputed through traffic. That is not the case. Although some trips clearly do begin and end in the Des Moines urbanized area, there are so many commuting trips that traffic loads on the interstate highways through the city are far greater than the imputed through traffic.
The average loads along the I-35/I-80 alignment are in the range of 40,000 or more, going as high as 46,900 at the border between Urbandale and Clive along the western part of the route and again at the east limits of Urbandale along the northern part of the route. The patterns here are actually consistent with those along I-80 through Lincoln, which has a similar alignment in relation to the city. The loads are somewhat less than the imputed or expected through traffic. The big difference comes when the MacVicar Freeway (I-235), running through the heart of the metro area, is included. Average daily trips on that road exceed 80,000 trips per day on more than 3.5 miles of the road and actually exceed 90,000 trips near its middle (42nd Street, near the western edge of Des Moines). The only segments below 50,000 are at its ends.
Taking the highest traffic load on I-235 (90,100 trips at 42nd Street) and the highest load on I35/80 (46,900 at two locations) produces a total average daily load for both roads of 137,000 trips. Comparing that to the imputed or expected through traffic of about 50,000 trips indicates that sixty-three percent (63%) of the trips on these two roads are commuting or other local trips. This stands in stark contrast to Lincoln, where a similar calculation actually yields a negative percentage, because the in-town traffic is less than the traffic at either side of the city. For traffic planners, the circumstances are even worse than these calculations suggest. Although through trips are likely to be distributed fairly evenly over the day and early evening hours, with some actually occurring overnight, commuting trips are almost all peak-hour trips.
ANALYSIS AND CONCLUSION
The conclusion is simple. With I-35/80 and I-235 through the Des Moines area, Iowa Department of Transportation officials are providing interstate freeways as a major element in serving local traffic needs. In contrast, with I-80 through Lincoln, Nebraska Bureau of Roads officials are primarily providing access to inter-city transportation. Which is better public policy, or whether they are equally valid but suited to different contexts, is an issue to be addressed by public officials and the citizens who elected them, not by scholars. Thus, this finding implies no value judgment. It is simply a finding, with its implications to be considered by others.
Although sewer service and annexation policies were clearly factors in these stories of urban form, the central finding of this study is simplethe reason that the Iowa Department of Transportation now faces the need to widen the MacVicar Freeway at great expense is because earlier officials at the Iowa DOT decided to build the MacVicar Freeway. That decision was a major contributor to the current urban form of the Des Moines metropolitan area, and that urban form in turn has created the demand for expansion of the MacVicar. The urban form and transportation pattern of Lincoln, Nebraska, a neighboring state capital, shows that there were, and to some extent still are, valid policy alternatives.
The lesson for transportation planners in other communities is fairly clear. If you want your city or region to look like the Des Moines metropolitan area, with heavy commuting loads on the interstate highways, relatively low densities and sprawling suburbs, freeze the boundaries of the central city, establish utility service boundaries that go far beyond it, and build major freeways to the growing suburbs. If you want to look like the Lincoln metropolitan area, annex to the central city the land necessary for development but then attempt to limit utility services to that area, and develop an integrated grid of public streets to serve local commuting needs; most important, do not ask (or encourage) state officials to improve the interstate highway system through town to provide improved commuting.
Funding for this project came from the U.S. Department of Transportation, through the Midwest Transportation Center, and from the Iowa Department of Transportation. Key participants in the project were faculty and students in the Department of Community and Regional Planning at Iowa State University, with the assistance of an advisory board. The Journal of Planning Literature published the literature review from this study in its November 1994 issue. Analysis from this study contributed directly to examples used in a Planning Advisory Service Report prepared by the principal investigator for the American Planning Association. Titled Planning, Growth and Public Facilities: a Primer for Public Facilities, it appeared in 1994 as No. 447 in the PAS report series. Interestingly, that report was cited by the Lincoln/Lancaster County Planning Department in a letter to the author as a significant influence in the preparation and adoption of the new Lincoln City/Lancaster County 1994 Comprehensive Plan; that region was, of course, one of the two included in the case study comparison for this report. The principal investigator presented much of the analysis and many of the lessons of this study at an Advanced Planning Commissioners training session sponsored by the Nebraska Planning and Zoning Association and at the Mid-South Planning and Zoning Institute at the University of Memphis, both in the spring of 1995.
Members of the project advisory board were Craig Marvick, Iowa Department of Transportation; Carol L. Swayne, City of Bellevue, Nebraska, Planning Commission; and Board of Directors (national), American Planning Association; Paul Wiegand, Director of Public Works, City of Ames, Iowa; Gary Pryor, AICP, ASLA, formerly Director of Planning, City of Omaha; Nebraska Gary Lozano, AICP, Assistant Director, Planning and Building Department, City of Des Moines, Iowa; and Barbara Becker, Ph.D., AICP, Associate Director, Drachman Institute, University of Arizona (formerly Southwest Missouri State University). Iowa State planning students who contributed to the project included Larry Dunkin, MCRP, 1993; Shawnda Hayes Groth, BSCRP, 1994; Regina Copic, BSCRP, 1995; and Monica Hearn, BSCRP, 1995.
- Bureau of the Census. Des Moines MSA, and Lincoln MSA, Summary Tables; , 1960, General Population Characteristics, Des Moines MSA, and Lincoln MSA, Tables 13; , 1970, General Population Characteristics, Des Moines MSA, and Lincoln MSA, Tables 16; , 1980, General Population Characteristics, Des Moines MSA, and Lincoln MSA, Tables 14; , 1990 General Population Characteristics; also, Census of Population and Housing: Summary Population and Housing Characteristics, Table 16 in respective state volumes, 1991; City and County Data Book, Table C, 1983; City and County Data Book, Table 6, 1972.
- All traffic data from City of Lincoln Transportation Department. 1994 24-hour traffic volumes (stapled). 1995.
- Iowa Department of Transportation. Volume of Traffic on the Primary Road System: 1992. 1993.