When cities like Detroit, Chicago, Cleveland, Pittsburgh, etc were built 10,000 year old forests cut down to build them. Business conditions have changed in the last 50 years, people have migrated and the structures are now being demolished. The environmental expense is enormous.
To prevent this occurrence in the future, modular cities should be built such that it is practical to move the city (structures, factories, roads, etc) a module at a time to new locations without demolishing the old and constructing new.
Further, as a city evolves it may outgrow the existing infrastructure. With modular construction it is possible to, for example, add surface rails to a road to increase capacity without demolishing the existing roadbed. Modular construction allows the city plan to change without huge expenditures and environmental damage.
Modular homes are in use in Japan, where homes older than three decades are rare. Homes built from shipping containers are also examples of modular homes that can be transported through conventional logistics systems. There are several proof of concept tests for modular roadways in which interlocking sections of roadway containing utility connections for water, sewage, electric power, natural gas, internet, etc are built in factories and installed in location to form roads, rail tracks, sideways, bicycle lanes, etc.
I think city of the future plans should consider modular construction technologies.