Keep in mind America was bulldozed for the car - there is precedent for large areas being massively transformed, and suburbs can absolutely be redesigned to be more walkable. A big issue with most suburbs is zoning that prohibits anything but single family residences. That means corner stores are literally illegal to build, alongside mixed use buildings, and other things that enable communities to be nicer to exist in, more friendly, and more convenient.

In addition to zoning laws, roads can be redesigned to be safer and more friendly to other modes of transit - and roads already need to be replaced every couple of decades, so theoretically within that time span every road could be improved in this way. More lanes have never reduced traffic in the long-term, but building infrastructure for denser modes of transit like busses or bikes or pedestrians does.