Michael Anderson writes on People for Bikes about "an alternative vision of the future of American transportation flickered to life, and then faded."- a move to develop separated bike lanes around the turn of the twentieth century. He points historian James Longhurst, who has written a paper (paywalled, of course) entitled The Sidepath Not Taken: Bicycles, Taxes, and the Rhetoric of the Public Good in the 1890s that looks at the history of the "sidepath movement."
The abstract starts with a statement that nails the fundamental problem with bikes, that they are not taken seriously as transportation.
After all, bikes are fun; in the United States, they are associated with childhood and are thought of as toys rather than meaningful components of transportation networks or economic development.
Sidepaths were built within the road allowance, before roads were widened into multi-lane paved arteries. But there wasn't enough money dedicated to funding them, and they were eventually subsumed by the car. Longhurst notes the effect they might have had:
If the paths themselves had continued to exist, they might have offered alternative suburban and interurban commuting options throughout the twentieth century. As cities and towns of America expanded, the suburbs would have bloomed along the sidepath networks linking them back to the urban center. The persistence of sidepaths might have provided some American cities with a built-in radial network of bicycle paths throughout the twentieth century — the very network that many are now trying to build or accommodate, with great difficulty, in the twenty-first.
Now that's bicycle urbanism, something that is just coming back into vogue.