GIS Tools for Transportation and Community Planning
This case study describes innovative applications of GIS techniques that TCSP grantees have used to support transportation and community planning.
The Federal Highway Administration's Transportation and Community and System Preservation Pilot Program (TCSP) has funded projects in all 50 states and the District of Columbia that link transportation, community, and system preservation practices. Many of these projects have applied innovative analytical approaches to assess and communicate the impacts of transportation and land use decisions on mobility, the environment, and economic development. Geographic Information Systems (GIS) have played a key role in supporting these analytical methods.
Walk travel times to schools in the City of Rockville, Maryland. GIS can be used to measure the accessibility impacts of adding links to the pedestrian network.
TCSP projects are demonstrating analytical methods supported by GIS for:
TCSP project sponsors are using GIS to enhance the transportation planning process as well as project design and development. GIS is being applied to support transportation and land use decisions at both regional and local levels. It is improving staff analytical capabilities as well as helping the public and decision-makers better understand the impacts of various alternatives. As a result, projects selected and designed by communities are reflecting a broader range of community impacts and more informed citizen input.
Furthermore, the results of project analysis show a common theme: that transportation and development plans proposed by TCSP projects will, indeed, achieve the program's objectives of reducing infrastructure costs and environmental impacts while increasing the efficiency of the transportation system.
Developing Regional Land Use Data
The idea of creating regional growth scenarios and modeling the transportation and other impacts of these scenarios is not new. Advances in GIS-based tools and data, however, have made it easier to construct and model such scenarios. At the same time, increasing concern over the impacts of development patterns have led more areas to undertake efforts to consider and analyze land use from a regional perspective.
One of the major challenges faced by TCSP grantees has been to construct regional growth scenarios that are not entirely hypothetical, but instead are consistent with existing constraints on development and realistic land use policy alternatives. Local comprehensive plans and zoning policies can provide a basis for such scenarios. Separate plans and zoning policies, however, are typically maintained by tens or even hundreds of local jurisdictions within a metropolitan area. Each jurisdiction typically uses a different classification system and many have plans only in hard copy format.
To support regional planning efforts, TCSP project sponsors in Phoenix, Arizona; Lansing, Michigan; and Salt Lake City, Utah have used GIS to integrate local land use plans and zoning into a regional database.
While providing useful information for planning, this is not a straightforward endeavor. Staff at the Tri-County Regional Planning Commission (TCRPC) in Lansing, Michigan explained how they assembled data from over 50 jurisdictions to support a regional growth visioning effort as part of a Fiscal Year (FY) 1999 TCSP project. Maps were obtained in both electronic and hard copy format; hard copy maps were scanned or digitally photographed. These maps were manipulated to create polygons corresponding to different land use areas, and to create identifying information for each polygon. Then, different land uses for each jurisdiction were converted into a uniform land use classification system. The resulting regional land use database was used as a basis for creating maps of population and employment under trend, alternative, and build-out scenarios which were used in public workshops.
TCRPC staff estimate that it took a technician approximately 25 percent time for three years to develop the regional database. This included collecting and analyzing data from other sources in addition to assembling local planning and zoning data. Keeping the data current will require additional staff time, as well as assistance from local jurisdictions in reviewing maps and providing updates as they occur. Nevertheless, the regional land use database in Lansing has been useful not only for regional but also for local planning. A number of local jurisdictions have requested copies so that they can easily identify planned land uses in adjacent jurisdictions.
Constructing and Testing
|Accessibility to employment||Regional travel demand model|
|Proportions of area within quarter-mile of bus route||GIS Analysis|
|Proportion of streets with sidewalks||GIS database previously assembled for bicycle and pedestrian planning.|
|Commercial land use mix||GIS analysis of county property appraiser's database|
|Presence of grocery store||County GIS|
|Presence of school||County GIS|
Three scenarios were compared: a "westward growth" (trend) scenario, an "activity center" scenario with growth concentrated in nodes on the current fringe of development, and a "compact development" scenario with growth concentrated in the center of the region. The car shedding model produced intuitive results that showed modest decreases in vehicle ownership rates and single-occupancy vehicle trip rates for the activity center and compact development scenarios compared to westward growth. The intra-zonal trip model, however, produced some surprising results that reflect broader limitations in the ability of four-step travel demand models to quantify certain types of land use changes.1 The total cost of this modeling effort, including a supplemental household travel survey, was approximately $180,000.
The projects described above focus primarily on testing the transportation impacts of alternative land use scenarios. Two TCSP-sponsored projects in Maryland have examined the reverse question: the impact of transportation on land use patterns. In 1996, the state of Maryland adopted a set of "Smart Growth" principles, which have been implemented through various state agency policies and programs. Under this initiative, the Maryland DOT established a policy to fund transportation infrastructure in locally designated "priority growth" areas while limiting potential growth inducing investment outside these areas.
Supported by FY 1999 and 2000 TCSP grants, the Maryland Department of Planning and Maryland Department of Transportation (DOT) developed methodologies to assess the land use consequences of transportation investments. The subject of the Department of Planning's FY 1999 project was the proposed widening of State Route (SR) 32 from a two-lane road to a four-lane freeway between I70 and SR 108 to address congestion and safety issues. In response to concerns that upgrading the road to four lanes would fuel growth outside of priority funding areas, an additional alternative was added to the study - a two-lane, limited access road that would improve safety but would not significantly increase capacity or operating speeds.
To evaluate the land use impacts of each alternative, the Department applied GIS data analysis and mapping in conjunction with a DOT-sponsored expert-panel approach to land use forecasting. The commute-shed of the road was first evaluated by mapping the origin locations of work-trips using the road, as estimated from the travel model covering the Baltimore metropolitan region. Land use data in the commute-shed were then mapped, including zoned densities, the amount of land recently developed, and the amount of land available for development. This provided background on growth trends, pressures, and opportunities in the area. For each alternative, the increase in accessibility to jobs (measured as the change in number of jobs accessible within 45 minutes) was then estimated from the regional travel demand model and mapped for each planning area. This showed the potential impact of the highway project on the desirability of each area for new development.
This information was provided to an expert panel who individually and jointly assessed the potential impact of each alternative. While opinions on the panel varied, most members felt that the four-lane alternative would provide a significant incentive for increased development in the study area, while the two-lane limited-access alternative would not. Staff from the Department of Planning therefore concluded that the four-lane option would contradict Smart Growth objectives and the desire to preserve rural land within the commute-shed In contrast, they concluded that the two-lane option would address safety concerns without contradicting Smart Growth principles.
Increase in job accessibility after expanding MD 32 to a four-lane freeway.
Supported by an FY 2000 TCSP grant, the Maryland DOT applied a similar expert panel method to forecast the land use impacts of highway and transit investments in the I270 corridor. The lessons learned from this study are being incorporated into a National Cooperative Highway Research Program (NCHRP) report for Project 836 on the use of expert panels in land use forecasting.
TCSP projects also have demonstrated the use of GIS-based models to assess community impacts associated with land use and transportation patterns. The outputs of these models include measures such as percent of population with walk access to transit, jobs/housing balance, average distance to closest parks or recreational facilities, percent impermeable surface area, and energy consumption from buildings and transportation.
"A developer proposed a suburban style grocery store next to a transit station. Using the PLACE3S model and the developer's own pro forma, we showed that if he incorporated a grocery store in a transitoriented development, his rate of return would increase from eight to ten percent."
- Nancy Hanson, California Energy Commission
The PLACE3S method (PLAnning for Community Energy, Environmental, and Economic Sustainability) is both a planning approach and a GIS-based analytical tool to support community land use and transportation planning. Utilizing parcel-level land use data, PLACE3S is designed to estimate the community, environmental, economic, and transportation benefits associated with alternative development scenarios. PLACE3S was applied in the Mid-City neighborhood of San Diego to help the community identify redevelopment options in conjunction with the completion of a freeway through the neighborhood. The model was used interactively in community workshops in order to help people understand the impacts of different zoning policies on redevelopment potential, energy use, vehicle travel, and other performance measures. The results helped shape a master plan for the neighborhood. PLACE3S also can be used for regional analysis, using less detailed but more broadly available data inputs.
The Dane INDEX model is a custom adaptation of the INDEX model to Dane County, Wisconsin. INDEX, which also utilizes parcel-level land use data, produces a variety of indicators associated with alternative development patterns, such as land use mix, pedestrian connectivity, and related changes in vehicle-trips. With the support of an FY 1999 TCSP grant, it has been applied in two pilot communities in the Madison area: the city of Stoughton and the rural township of Vienna.
Like PLACE3S, INDEX can compare indicators for two or more alternative land use scenarios. The analyst must supply the characteristics of each scenario, including a street layout and land use type and planned densities by parcel. If the model is applied to a specific proposed development, computer-aided design (CAD) files from the developer can be imported into the model's GIS environment.
Dane County added two components to the INDEX model that were of particular interest to local planners: fiscal impacts and storm water runoff. The fiscal impact model, a spreadsheet model linked to the GIS land use data in Dane INDEX, was developed by a local firm and utilizes locally collected data, including municipal budget information from the last 10 years and interviews with local staff. An existing storm water model developed at Purdue University, known as Long Term Hydrologic Impact Assessment (LTHIA), was also integrated into Dane INDEX. From land use, soil hydrology, and rainfall data, LTHIA estimates runoff, recharge, non-point source pollution load, and other hydrologic impacts of land use changes. LTHIA is available separately as a spreadsheet application, a web based application, or as an ArcView extension.
Two alternative street and parcel layouts for a subdivision in Stoughton, Wisconsin, as shown in the Dane INDEX model. The blue lines are sidewalks. The color on parcels represents walking distance to the nearest park (green is closer, red is farther). Average walking distance from all parcels is shown.
Courtesy Dane County Planning and Development Department.
The effort required to develop the data to support the Dane INDEX model will vary depending upon the availability of local land use data. In Vienna, much of the data were already contained in the county's GIS databases, although some format conversion was required. For the Stoughton pilot study, a local cartographic firm developed data by converting orthographic photos, county parcel lines, tax assessor data, and other available data to digital layers, including street centerlines, sidewalks, building footprints, impervious surface area, and parcels with land use categories. The total cost of the Design Dane project effort, including model customization and pilot application, is estimated at $445,000.
GIS tools are increasingly being used in conjunction with global positioning systems (GPS) to gather data on pedestrian facilities and assess needs. With the support of an FY 2001 TCSP grant, the City of Rockville, Maryland is using GIS with GPS to create a citywide inventory of pedestrian, bicycle, transit, and roadway facilities. The data are being collected by local college students using handheld personal computers and GPS devices. Examples of data include bus stop and transit line details; sidewalk specifications; bicycle facility specifications and speeds; roadway types, cross sections, and congestion levels; and truck restrictions.
An initial use of the data is to develop pedestrian travel time contours to area schools using a GIS network analysis module. The city plans to use the database for applications such as quantifying the multi-modal accessibility benefits of capital improvements such as sidewalk extensions.
The cost implications of alternative development patterns are increasingly of interest in many areas. Proponents of Smart Growth believe that more compact development patterns can reduce infrastructure costs, both for regional infrastructure, including major roads, transit systems, and utilities, and for local roads and utilities. TCSP funds have helped project sponsors in Kansas City, Missouri; Salt Lake City, Utah; and Madison, Wisconsin develop fiscal impact models for assessing the consequences of alternative development patterns.
In Salt Lake City, a comprehensive assessment of regional and local infrastructure costs was performed as part of the Envision Utah regional visioning project, which compared a "trend scenario" with a "quality growth strategy" developed through an extensive public participation process. Infrastructure costs were estimated at three levels: regional, local offsite (municipal), and local onsite. Regional highway, transit, and utility needs under each growth scenario were assessed through modeling, and costs associated with these needs were estimated. Local, offsite infrastructure costs per unit of development were then estimated from municipal impact fee studies of selected municipalities and special districts. Onsite costs for roads and utilities were estimated using a simulation model to evaluate different subdivision designs. Offsite and onsite costs were estimated as a function of development density and whether the land was "raw," infill, or reuse. Total costs for each regional growth scenario were then estimated using the GIS land use data developed for each scenario. The infrastructure cost estimates were one of a number of performance measures provided to the public to help them compare the inputs of different growth scenarios.
The Mid-America Regional Council (MARC) in Kansas City, Missouri also created and applied a cost-of-development tool as part of its Smart Choices FY 1999 TCSP project. The goal of this project was in part to educate developers, local officials, and the public about the benefits and inputs of different growth patterns. In contrast to Envision Utah's regional model, MARC's spreadsheet-based tool was designed to be applied at the site level. MARC used the tool to compare the costs of alternative site development plans for six case study sites selected from throughout the region. This effort complemented a public design process to create transit-supportive development designs for each site as an alternative to standard auto-oriented development patterns.
The alternative site designs typically included a greater amount of mixed-use development and higher residential densities, with the same amount of overall development. Unit costs for the infrastructure components - including streets, sidewalks, and utilities - were compiled in consultation with developers, engineers and subdivision planners who work in this area. Total and per-acre costs for each development were then calculated based on the estimated length of infrastructure and land area devoted to each type of development. The analysis found that overall costs were lower for the "alternative" than for the "conventional" developments at four of the five sites evaluated, although the average difference in costs was relatively small (3.5 percent across all sites). The total cost of the cost-of-development analysis was approximately $150,000, including consultant fees and staff time.
Awareness is increasing of the potential habitat fragmentation and destruction and related ecological impacts caused by transportation infrastructure and land development. Fortunately, transportation facilities and land use policies can be designed to minimize impacts on wetlands and other sensitive natural areas.
An FY 2000 TCSP project sponsored by local communities in McHenry County, Illinois and the Conservation Research Institute is working towards a sustainable transportation and land use plan for the Route 47 Kishwaukee River Corridor. Route 47 transects much of the headwaters of the Kishwaukee River, which has been rated by the state of Illinois Department of Natural Resources as a Unique Aquatic Resource. However, the eight-mile corridor is also experiencing strong growth pressures due to its location on the suburban fringes of Chicago. The purpose of the TCSP project was to bring together local jurisdictions, state agencies, and the general public to create a corridor transportation and land use plan that protects the Kishwaukee River and adjacent natural areas.
Project sponsors used GIS analysis to support the development of corridor alternatives, including the placement of roads and the designation of land uses. The first step was to collect comprehensive plans from all six jurisdictions in the corridor and digitize these plans. A build-out analysis was performed by cropping areas that were already built (based on aerial photographs), and then calculating total build-out potential based on densities and land use in the comprehensive plans. The environmental GIS data were used to map suitable habitat for five ecological indicators: sandhill cranes, frogs, the darter (a fish), vegetation remnants, and salt-tolerant plants in wetlands.
Next, an alternative, conservation-based land use plan was developed. This alternative includes the same amount of total development by type, but concentrates it in areas of lower ecological sensitivity, away from wetlands, streams and rivers, and other critical areas. The GIS data were used to design alternative land use designations and transportation alignments that would reduce the impacts on the indicator habitat areas. In addition, GIS analysis allowed the impact of each transportation and land use alternative to be quantified, through measures such as percent of frog habitat lost.
The alternative plan considers transportation concepts such as road or interchange realignments to avoid wetlands. Transit options, including locations for park-and-ride lots and potential future bus and rail service, were investigated to minimize road infrastructure requirements. Transportation impacts were assessed using a trip table-based spreadsheet model. While an alternative plan has not yet been finalized, transportation concepts were discussed with the county transportation agency as well as the Illinois DOT to ensure their feasibility. Successful implementation will also rely on the cooperation of local jurisdictions to revise land use plans consistent with the recommendations of the study.
"GIS is helping us develop a multijurisdictional transportation and land use plan that accommodates development while respecting the natural environment of the corridor."
- Charles McGhee Hassrick, Conservation Design Forum
The total cost of this corridor planning effort, including GIS land use and environmental data collection and analysis, public involvement and outreach activities, and plan development, is estimated at $310,000.
A major effort is also underway to integrate transportation, land use planning, and habitat conservation in Riverside County, California. Funded in part by an FY 2000 TCSP grant of $435,500, the Community and Environmental Transportation Acceptability Process (CETAP) is directed at identifying and preserving future transportation corridors while minimizing environmental impacts and coordinating local land use planning. GIS is helping the county use data on high priority conservation areas, identified through a parallel multispecies habitat planning effort, to select transportation corridors that reduce ecological impacts by avoiding sensitive areas or minimizing fragmentation of these areas.
With the aid of geographic information systems, TCSP projects have undertaken analytical efforts to quantify the transportation, infrastructure cost, and other community and environmental impacts of local and regional development patterns. These projects have typically compared a "trend" growth scenario with one or more "alternative" scenarios in which the same amount of development is concentrated in a more compact pattern in infill locations, transit nodes, villages, or other activity centers. While each of these projects was undertaken in a different context, using different assumptions and tools, it is interesting to compare the results of these analysis.
Western Riverside County, California. Transportation corridor alternatives are shown overlaid on potential habitat preserve areas identified through a countywide habitat conservation planning effort. GIS is helping the county preserve rightofway for future transportation needs while minimizing ecological impacts.
Courtesy Riverside County Transportation Commission.
In most cases, measures of traffic impact - whether total VMT, vehicle-trips., percent of travel under congested conditions, or average trip time - were improved for the alternative growth scenarios. An interesting finding from the Lansing work was that congestion was slightly higher in the short run - probably due to greater concentration of development in specific areas - but significantly lower in the long run (at build-out), due largely to shorter trip lengths resulting from a more compact development pattern. The findings of shorter trip lengths, along with lower levels of congestion, are reinforced by modeling results from the Charlottesville and Salt Lake City TCSP projects.
The Gainesville work shows that land use variables can be incorporated into models of vehicle ownership to more fully reflect the impact of future land use policies. This analysis, however, also showed a somewhat surprising finding of fewer single-occupancy vehicle trips but higher VMT under one of the alternative scenarios. Additional research is needed to determine whether this finding is realistic, or whether it reflects limitations in the ability of current four-step travel demand models to address micro-scale land use changes.
Another common theme from the results of TCSP analysis efforts is that net infrastructure costs are lower for the alternative than for the trend growth scenarios. Regional infrastructure costs are lower because less roadway investment is required to serve newly developing outlying areas, and because lower VMT requires less enhancement to existing capacity. In the case of Salt Lake City, the reduction in regional road costs was enough to more than offset a significant increase in transit investment. Findings from Salt Lake City also showed that local infrastructure costs were lower under conditions of higher residential density and for infill versus greenfields development. The Kansas City analysis suggests, however, that simply changing the layout of development on a specific site (e.g., increasing the mix of uses and local density) may have a relatively small impact on infrastructure costs, even though the design changes may produce other benefits such as greater walkability and land preservation. The cumulative benefits of land use design changes throughout a region may be greater than the sum of benefits of design changes at individual sites, when evaluated in isolation.
Findings from environmental and community indicator models are consistent with what might be expected based on the land use and transportation characteristics of alternative scenarios: pollutant emissions are reduced, land consumption is reduced, and transportation options are increased because of more pedestrian and transit-oriented design characteristics.
|Project Location||Scenarios Compared||Transportation Impacts||Infrastructure Impacts|
|Gainesville, Florida||“Compact” and “activity centers” versus “regional trend”||
|Lansing, Michigan||“Wise growth” versus regional trend||
|Kansas City, Missouri||“Alternative” versus “conventional” (5 sites)||
|Salt Lake City, Utah||Regional “quality growth strategy” versus “trend”||
|Charlottesville, Virginia||“Urban” and “Town Center” versus “Dispersed” regional||
A number of conclusions and lessons learned emerge from this review of GIS as being used through the TCSP program:
"We succeeded in developing a simple yet reliable tool that has helped people understand the impacts of future growth patterns, not only through quantitative measures but also through visual depictions of what growth might look like."
- Hannah Twaddell, Former Assistant Director, Thomas Jefferson Planning District Commission
San Diego, California
McHenry County, Illinois
Kansas City, Missouri
Salt Lake City, Utah