This isn't a subject with easy or even straightforward answers.
There's no question that the rise of the automobile in the 1920s and later the development of the interstate highway system had a profound effect on city planning in the US. But the decline of interurban streetcars started well before the latter, and in many instances, even before the former; in which case, the interstate system accelerated an existing problem rather than creating it.
Nearly all streetcar/trolley lines were operated by private entities, and carried significant capital costs and ongoing maintenance concerns. Shortsighted agreements that gave monopoly or near-monopoly status to lines in exchange for fixed fares (the "five cent fare") . Those same agreements were financial albatrosses in the face of post-war inflation, and lines had varying degrees of success in pushing for minor fare increases. In New York in 1919, streetcar lines in Albany, Syracuse, Utica, and Troy were allowed to increase fares to six cents while New York City rejected any increase.[0] By the 1920s, many of the country's streetcar lines had gone out of business; almost all had major financial struggles. This quote sums up the challenge:
> . Charles E. Chalmers, receiver of the bankrupt Second Avenue Railroad, despaired of gaining relief. “The five-cent street car fare has become an American
institution, and, as railroad operators, we must realize that this question of fare will be constantly with us. It will be a stumbling block as long as street cars run, and in New York City our people are wedded to the five-cent fare.”2
Attempts to ease tax and decades-old paving requirements on streetcar companies were met with failure, even as they further undermined cashflow. "“During the ten years from 1911 to 1920, the street railroads of New York State each year expended for paving alone an amount equal to an average of 23.4% of their net income, or to put it another way, the paving expense has amounted to approximately 5% of the total operating expenses of street railroads during that time" (60). Over 35% of NYC's paved area was maintained by street railroads. Worse, the railroads wound up subsidizing automobiles. Per J.C. Thirwall of GE's railway engineering department, "So long as municipalities offer the use of smooth pavements free of charge to all commercial vehicles and compel the railway company to pay not only for its own tracks but for much of the paving as well, a considerable bonus is offered to users of buses" (61). It also didn't help that politicians and the public at large saw street railroad owners as the prototypical villains of their day. Taken together, it all eventually combined to harm the streetcar's ability to compete with buses.[1]
General Motors may have played a role in the final waning years of the streetcar, but only after the streetcar was already dying well before the federal government started subsidizing highways. Other factors were also involved. * Suburbanizing the Masses: Public Transport and Urban Development in Historical Perspective* is a fascinating series of essays analyzing how public transportation have shaped city planning since the 1850s.[2] A number of the essays cover street railways in particular.
The same goes for the development of sprawl; there's an interesting study from 2015 that looked at street connectivity to measure sprawl and suggests that it predates the highway-centric city planning during the 50s that's widely labeled as the starting point:
> First, Fig. 1 indicates a rise in sprawl since the mid-1920s, with an acceleration after 1950. The early beginning of sprawl is notable, given that it predates the postwar era of mass car ownership. However, it provides quantitative evidence to confirm historical accounts that date the emergence of cul-de-sacs and similar departures from gridiron street patterns to the early to mid-20th century. Southworth and Ben-Joseph (17), for example, note the influence of the 1928 design, with cul-de-sacs prominently featured, for Radburn, New Jersey; they also point to the influence of recommendations for cul-de-sacs in reports by the Committee on Subdivision Layout (1932), Federal Housing Administration (1936), and Institute for Transportation Engineers (1965). These discrete events do not capture the more gradual evolution in street network design from the 1950s through the early 21st century, but our results closely match the archetypal patterns reported in ref. 17 and illustrated in the Lower panel of Fig. 1. [1]
There have absolutely been major negative consequences arising from how highway financing and subsidies were handled in the 50s. But many of the problems stemmed from how highways were viewed as "the greatest single element in the cure of city ills."[4] The "artery" model was used by city planners to effectively gut their own cities, possibly in a way that Eisenhower himself never expected.[5] When city planners wanted to get rid of poor people and "slums," which were predominantly African-American, the solution was to pave over their neighborhoods. The federal government even helped them pay for most of it. Highways became a cheap, easy tool for city planners as a result of these policies, and that had some truly disastrous consequences.[6] Setting aside the social consequences, cities were paving the road for their tax bases to--literally--leave town. There are a number of excellent books and essays on the subject. Despite that, it's important to recognize that there's a difference between the bulk of the interstate highway system and its most problematic parts in and around urban cores.
Anyhow, getting back to the article, it's written in the context of the system--flaws and all--that we've got right now. In this context, completing the missing link on I-95 does increase mobility. That's a given. More than just this stretch of highway, there are trillions of dollars worth of private development and public infrastructure that have been built in an America with the highway systems as-is. Of that infrastructure, there's a $2+ trillion maintenance funding gap. Worse yet, as elements reach their designated end of life, it all will eventually need to be replaced. The sum total of that bill is yet to come due.
Would we have been better off had city-planners not seen highways as the hammer to their perceived nails (i.e. problems--redevelopment, transportation/mobility, etc.)? Probably. The good news is that modern city planning recognizes this, and attempts to correct for some of the consequences. Unfortunately, this can only happen incrementally. That's a slow, decades-long process and it's easy to miss just how long it's going to take or the kind of compromises that are necessary.
We're getting there. But in the meantime, we still have to maintain and update all of the rest of our infrastructure--even that which represents the biggest mistakes made during highway development in the 50s.
0. https://zacharyschrag.com/wp-content/uploads/2011/06/41-1sch...
1. https://www.citylab.com/transportation/2013/06/be-careful-ho...
2. https://www.amazon.com/Suburbanizing-Masses-Development-Hist...
3. http://www.pnas.org/content/112/27/8244
4. https://www.theatlantic.com/business/archive/2016/03/role-of...
5. https://www.citylab.com/transportation/2011/11/death-row-urb...
6. https://papers.ssrn.com/sol3/papers.cfm?abstract_id=1392502