The global geography of freeway interchanges

Freeway interchanges are an essential, though often overlooked, transport infrastructure. A range of designs have been developed over the past 100 years, most originating in the United States. These designs have spread throughout the world, but there has been very little examination of where they were adopted or of which designs proved most popular, nor of whether new designs have appeared. This research mapped every freeway interchange in the world, classifying the design of all 61,092 found and examining potential explanatory factors such as population and transportation indicators, as well as political choices for their frequency and design. The primary explanatory factor for interchange design choice was whether a country’s freeway system was free or tolled; the choice of which engineering standards to follow may also be a factor. Interchanges will grow in number throughout the twenty-first century and could be important in reshaping urban geographies around the world.