Isochrone

The Portland metropolitan region has seen recent forecasts that indicate the population is growing much faster than anticipated, with an increase of 1 million people in the next 25 years. At the same time, transportation funding is declining and global instability has fuel and construction costs soaring. This presents challenges to the mobility of people, access of freight, land use efficiency, and human and environmental health.

The maps represent the 2005 base year automobile travel times (in minutes) from select urban and industrial centers. These isochrones illustrate accessibility in different areas of the region. They will be analyzed and compared to isochrones produced from transportation networks modeled for future years. Modeling a variety of investment scenarios gives planners the ability to visualize the impacts of infrastructure changes in the transportation system to determine the best match to our land use targets.

Metropolitan Planning Organizations (MPOs) grew out of a need to manage growing federal investments in transportation. The Federal-Aid Highway Act authorized the federal government to pay 90 percent of the cost of the Interstate Highway System and had a major transportation planning requirement: Urban areas with populations of 50,000 or more are to engage in “continuing, comprehensive, and cooperative” transportation planning.

Oregon has six MPOs, covering the metropolitan areas of Portland, Salem-Keizer, Corvallis, Eugene-Springfield, Medford-Ashland, and Bend. Oregon is likely to see more MPOs in the near future as more cities reach a 50,000 population. Literature suggests that beyond 45 minutes, commuting drops sharply in large urban areas. A multistate network dataset was created to perform the free-flow travel analysis in ArcGIS Network Analyst, starting from the point of origin—the urban center of each MPO. Calculating and visualizing travel time isochrones in nine five-minute intervals for a total of 45 minutes allowed planners to better understand future land use pressures.

A clearer picture of the connection between developing super-regions is achieved when change in transportation volume data (1998-2004) and average annual daily traffic volume data (2004) are transposed on the base map and travelshed isochrone. These areas of economic activity are evolving from centers of agriculture into hubs of modern economic growth, and it is important to plan for the future.

Courtesy of Matthew Hampton.