Robert Moses was essentially the guy that remade NYC from the 1930s to the '60s, by opening up the city to cars and downplaying the importance of public transit as well as being a racist SOB.
Let's flip it. Although alt-Robert Moses is just as powerful and successful as OTL's Robert Moses he's (IMO) a good guy and instead of disliking blacks, preventing mass transit from accessing his shiny new parks, and so forth he pretty much does the opposite.
Considering that in the field of urban planning Robert Moses was one of the most influential figures post-war him having a different take on things not only alters NYC, but should also effect major cities in general.
(For sports fans, alt-Moses mean the Brooklyn Dodgers stay there instead of moving to L.A.)
(For rail fans, alt-Moses saves the NYC streetcars that are still around, a bunch of el-trains, and possibly saves streetcars in other cities like L.A. as well as surely needing to build more suburban lines if he isn't building a lot of roads.)
(For NYC folk this not only has a decent chance at saving Penn Station, it also means a lot more el-track: IRT Ninth Avenue Line, most of the IRT Second Avenue El in Manhattan, and the BMT Fifth and Third Avenue Lines and most of the BMT Fulton Street Line in Brooklyn will all be saved. A concern for capacity will outweigh concerns over redundancy.)
So, NYC embarks on a major expansion of the subway system as Moses uses the vast bridge toll revenue he controls to seize the capital construction part of the transit system and put it under him, instead of the city.
Furthermore his mass transit focused ideas will act as a powerful counterweight to the big car companies, and should save streetcars and expand subways in major cities.
He can't stop suburbs, but mass transit plus presumably enhanced commuter rail will also serve to slow widespread ones down.
I'm not sure if we can get Europe/Japan style highspeed rail out of this, but it's quite possible in a more transit/rail focused United States.
Thoughts?