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Summer 2006

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Illinois Department of Transportation Develops Statewide Road Network with GIS

The Roots of a Statewide Transportation Coalition

  click to enlarge
IDOT event data dynamically segmented onto routes created on the conflated basemap.
Originally designed to support data management functions, the Illinois Department of Transportation (IDOT) GIS roadway basemap featured centerlines representing only the road segments maintained by the IDOT inventory. It was missing an additional 30,000 miles of local roads maintained by local agencies. With the resulting inability to geocode addresses, the inadequacy of the limited roadway base became especially clear as more and more agency offices began implementing GIS. Despite using GIS for 15 years, IDOT's benefits were limited because of the way the road inventory and transportation information was stored.

These and other data constraints restricted the abilities of many state bureaus to take full advantage of the capabilities offered by the GIS technology they wanted to use. Furthermore, many state agencies were unable to use the IDOT roadway base for their GIS applications due to the incomplete centerline data.

Because of these issues, IDOT took the lead in developing a statewide road network to share across bureaus and with other state and local government agencies. The new statewide road network can be used for geocoding incident management and tracking and additional layer (boundary) development.

The Statewide Road Network Solution

In March 2005, IDOT requested proposals to develop a comprehensive statewide road network and create the appropriate tools and organizational framework for road network maintenance. Additional services were requested to develop an overall GIS needs assessment and strategic plan for expanding the use of GIS within the agency.

A team proposed by Esri Business Partner GIS Solutions, Inc. (Springfield, Illinois), was selected to combine (conflate) statewide road network data, as well as provide a vision for using GIS within the agency to improve internal business processes and make better information available to the public. As a basis for the network, GIS Solutions' NAVTEQ road dataset was selected, which included detailed local road data that could be added to IDOT's data and provided regular updates. The dataset was created using a combination of source data and fieldwork that included physically driving the roads to collect and position key attributes necessary for navigation.

Creating the IDOT Statewide Road Network Geodatabase

To create a roadway geodatabase that included local roads and had geocoding capabilities, NAVTEQ roadway geometry and attribution were used and combined with the IDOT roadway attribution. Conflation aligns the features of two geographic data layers and then transfers the attributes of one to the other. IDOT staff conflated their GIS with the NAVTEQ data, allowing the dynamic segmentation of event data onto the new roadway geometry. A linear reference system was created onto which IDOT roadway data was dynamically segmented. This method achieves far better results than an attempt to conflate all attributes onto features in a commercial dataset.

The conflation efforts included more than 115,000 miles of road and took approximately six months. Out-of-the-box ArcView tools were used to complete the majority of this task; however, some customization to develop editing tools was accomplished with ArcObjects programming. Taking advantage of the versioning and storing capabilities offered by ArcSDE, multiple editors were able to work on versions of the data, which were later reconciled, creating a production dataset stored and accessed in ArcSDE on an IDOT server. Maintenance of the dataset is routinely accomplished using a custom maintenance toolset built using ArcObjects within the ArcGIS environment.

In addition to the conflation effort, the team developed an automated process using ArcGIS tools and the geodatabase to extract only the changes from NAVTEQ's quarterly updates for integration. This significantly reduced the amount of processing time IDOT needs to integrate and update the new roadway base while providing regular roadway updates to all GIS users.

"The ability to provide full coverage of the state's roadway system," says Cecil Renshaw, application development chief, Bureau of Information Processing, IDOT, "not only to IDOT users but also to users in all government agencies in Illinois is a significant enhancement to GIS in Illinois."

Illinois GIS Transportation Coalition

The strategic plan and statewide road network conflation prompted IDOT to reach out to other government agencies in the hope of creating a long-term relationship with local governments through a newly created GIS Transportation Coalition. The vision of the GIS Transportation Coalition is to serve as a forum to share GIS transportation information between all levels of government.

The catalyst for the GIS Transportation Coalition was the unique license and data-sharing agreement. Through IDOT's three-year data purchase agreement, NAVTEQ has granted the state of Illinois an enterprise license allowing state and local units of government use of the data for applications supporting internal agency operations to an unlimited number of users at no cost. All Illinois government agencies may also edit, update, and/or enhance the data for their agency applications and develop noncommercial applications that display the data to the public via the Internet. This unique arrangement is not only a cost savings to state and local agencies, but it also provides a first step in having governments use the same base dataset.

Already, 38 local government agencies and metropolitan planning organizations have requested the new conflated Illinois roadway data to use at the local level. IDOT hopes to collect local road and other transportation data from city and county governments to continue to build a comprehensive and accurate road network for Illinois. It is anticipated that the data gathered through the coalition efforts will be a comprehensive set of information and source data for statewide road coverage that can be used for location analysis, routing, and other decision-support applications for all persons requiring access and information about the state's transportation network. IDOT believes that the digital road network will be a catalyst to share information across government agencies; reduce redundant efforts in GIS; and be an enduring and improving dataset, incorporating ongoing changes and improvements.

"Successful development and deployment of a digital road network for IDOT will provide unlimited opportunities to deliver core business services to the public using GIS applications," says Mark Kinkade, chief information officer, IDOT. "IDOT is pioneering a course that promises to lead us into a fully integrated enterprise GIS that encompasses potentially every government agency in Illinois."

More Information

For more information, contact Mark Kinkade, IDOT (e-mail:, or Bob Lindquist, vice president, GIS Solutions, Inc. (e-mail:, tel.: 217-546-3635). Visit the IDOT Web site to access the new traveler information network (

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