EMME/2 Helps Transportation Planners:
ArcInfo-Based Highway Project Modeling

Published in: ArcNews, Vol. 17, No. 4, Winter 1995, p. 15.

Abstract:

New software, now called the 2.11 Toolbox (sorry -- link temporarily unavailable), originally developed by Christopher Eykamp at Metro in Portland, Oregon, helps transportation planners build and maintain multiple EMME/2 simulation networks using the GIS package ArcInfo. The software also makes possible the re-import of EMME/2 data into ArcInfo for further display and analysis.

Full Text:

The Portland, Oregon regional government Metro is one of the few independently elected regional governments in the United States. It is responsible for many regional services, such as coordinating recycling efforts, running the parks and zoo, and transportation and land use planning. In order to simplify the modeling process used in Metro's transportation planning, the Planning Department has recently finished coding a comprehensive ArcInfo-based highway project modeling management system, which builds simulation networks for EMME/2, a transportation network analysis tool. The software, designed and coded at Metro, helps transportation planners perform congestion projections, air quality analysis, and other transportation studies, and solves the problem of maintaining many different simulation networks, each for a different year and construction scenario.

"EMME/2's interface opens up many possibilities for data calculation and display," said Dick Walker, manager of Metro's travel forecasting section. "It releases the chains of constraint and provides the analyst with an abundance of ways to creatively investigate."

EMME/2 is a sophisticated software package that helps transportation planners model how people move across a transportation network under a given set of conditions. Like ArcInfo, EMME/2's networks consist of arcs and nodes, with arc-based attributes such as capacity and the number of lanes in either direction. Additionally, EMME/2 represents a two-way street with two arcs (called "links"). The first step, before any coding could take place, was to move a 1994-1995 EMME/2 network into ArcInfo as an arc coverage and collapse the unidirectional EMME/2 links into bi-directional ArcInfo links. This became the "base network," which looks like a simplified schematic view of the regional street network.

Because of the need to simulate future scenarios, Metro's planners needed to know how the street network was expected to change over time. The scope, nature, and even existence of future road, transit, and bicycle projects are constantly changing, so the planners needed a way to track these projects and ensure that their models accurately reflected the most recent project proposals. The best way to do this was to create a dynamic segmentation data layer over the base network. The routes carry information that is relevant to the project as a whole, such as the project name, and the date it will be completed. The sections carry data that are specific to a particular link only, such as the capacity the future street will have or the future number of lanes. A sophisticated multithreaded user interface was developed to simplify the entry and maintenance of project data. (A similar interface has been developed to handle transit coding.)

To see how a project is coded, the user simply selects the project they want from a list of project titles or ID numbers. The screen will zoom in on the selected project and information about the project is displayed on a menu showing capacity, number of lanes, and other relevant information for both directions of the selected link. The same information is displayed for the base network, making it simple to see what the project does and how it will be modeled. The user can edit any of the information or select a new project to view. Projects can be created or deleted in a similarly easy fashion.

When it comes time to build a network for EMME/2, users are presented with a menu that asks them to build an English-language description of the network they want. A typical sentence might be, "I want all projects built after 1995 and before 2000 that are in the TIP, except for project #10." (The TIP is a list of projects that are eligible for federal funds.) The system then turns this sentence into a valid ArcInfo select statement and the chosen projects become selected. The project attributes are copied onto the base network, thus modifying the characteristics of the arcs. The coverage, as well as the desired transit information, is then converted into a format that EMME/2 can read.

One problem that was encountered early on was the differing representation of links in ArcInfo and EMME/2. This difficulty was overcome by maintaining two copies of each attribute on the ArcInfo arcs, one for each direction, using the arc's "arrow" as a reference. For example, to record the number of lanes in each direction, one would use the attributes lanes_ft to indicate the number of lanes in the direction of the arrow, and lanes_tf for the number of lanes in the opposite direction. It is important to keep track of the directions of the routes and sections that contained the project data, and make sure the _ft and _tf values were properly entered and aligned with the underlying arcs, but these complexities are hidden from the user by the interface.

In addition to producing simulation networks for EMME/2, the software has the capability to produce documentation showing the location and scope of the different road projects. The software can even combine plot files from EMME/2 with location maps and other ArcInfo output on the same page to make powerful illustrations showing how a particular project is modeled. Metro has used this feature to produce a book detailing exactly how they modeled each street improvement project, making it much easier to coordinate network review among the many local jurisdictions in the Portland Metropolitan Area.

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