In the 1950s and 60s, students of transportation focused on building infrastructure and applied lessons from the physical sciences to designing mobility. Mobility was facilely linked to the engines of economic growth and expanding GDP. In time, that perspective was replaced by a focus on transportation systems and networks. There was a newfound emphasis on environmental impacts, land use and intermodal freight. There was also a growing concern on unpriced externalities.
Today, Joseph Sussman explains, with many of those problems still unsolved, transportation has entered a new phase — a period of immense complexity or CLIOS, which stands for complex, large scale, interconnected, open and sociotechical, that is becoming the mantra of transportation engineers. While it is not as far-reaching as "chaos" to a physicist, it is an approach with far-reaching consequences for the transportation field.