A robust body of empirical induced travel research demonstrates that as roadway supply increases, vehicle miles traveled (VMT) generally does as well. The evidence is particularly strong with respect to induced travel from major roadways like interstate highways (Federal Highway Administration class 1), other freeways and express ways (class 2), and other principal arterials (class 3). For example, the NCST California Induced Travel Calculator -- used to estimate additional induced VMT from expanding capacity of major roadways, and recommended for this use in Caltrans' Transportation Analysis Framework -- only applies to publicly owned facilities of FHWA class 1, 2, or 3. Previous research in this field have found limited empirical evidence for the relative magnitude of induced travel from expanding minor arterials, collector streets and none for auxiliary lanes, ramps, or other interchanges. The purpose of this project is to explore the induced travel effects of categories of roadway expansions not currently covered by the Induced Travel Calculator, including minor arterials, interchanges, on- and off-ramps, and non-general-purpose facilities.
