Transportation planning

Indiana Business Review, Summer, 2008 by Stephen C. Smith

The demand for transportation services is based upon the relationship between land use and trip making. A large portion of travel is generated by interactions between population concentrations (as measured by households) which tend to produce trips and employment centers which tend to attract trips. A basic measure of travel demand is vehicle miles of travel (number of vehicles times distance traveled) or VMT. Based on the Indiana Department of Transportation's current population and employment forecasts (2000 to 2030) applied through the statewide travel demand simulation model, we see the total growth in VMT increasing 38 percent over that thirty-year period and truck-related VMT increasing by 85 percent. Freight-related traffic is expected to increase more rapidly than passenger traffic due to the increased dispersion of population and employment, increases in income driving demand for consumer goods and the longer trip lengths associated with the global economy.

The future population projections outline a continuation of recent trends in increased suburbanization and growth of the major metropolitan areas. This is resulting in a shift of travel patterns from the more traditional radial suburban-to-downtown business district patterns to suburban-to-suburban circumferential travel. Increased congestion levels in these outlying areas will place additional demands on making roadway improvements in these lower density areas experiencing suburbanization.

The aging of the population will also affect travel demand. Personal travel is closely related to the lifestyle of the individual. Persons exhibit peak travel activity at 35 to 50 years of age. As the population ages, the rate of trip making declines, providing a moderating impact on future travel demand growth. This moderating impact will be most pronounced in the rural areas of the state where the median age of the population tends to be higher.

INDOT will use the new 2005 to 2040 population projections as a key input into the update of the statewide travel demand simulation model as we advance our horizon planning year from 2030 to 2035.

Stephen C. Smith, AICP: Manager, Long-Range Transportation Planning Section, Indiana Department of Transportation