In the late 1930s, the RPA successfully prevented Robert Moses's proposal to build a bridge between Battery Park and Brooklyn, resulting in the Brooklyn-Battery Tunnel being built instead.

During World War II, the RPA worked to address housing, transportation, and civilian protection efforts, particularly due to the convergence of workers in defense industries.

Following World War II, population growth exploded in the suburbs, as opposed to New York City and other urban areas as it had been decades prior.

RPA advocated for comprehensive community planning, improved building codes, and large-scale development of regional city centers.

These ideas were implemented in places such as Fresh Meadows and Forest Hill Gardens in Queens, and Radburn, New Jersey.

In the 1950s, some board members of the RPA considered the dissolution of the organization, claiming that the goals of the First Plan had largely been completed with the construction of the Verrazano-Narrows Bridge.

Instead, the RPA was tasked with analyzing the impact and alternatives to suburban sprawl, particularly the rapid rise in lot size requirements and scattering of nonresidential development.

They advocated against the construction of a fourth major airport in the region, instead seeking ways to minimize air travel growth and improving runway capacity.

In 1995, the RPA spearheaded the effort to transform Governor's Island from an abandoned Coast Guard base to an urban park.

RPA created several one-hour documentaries which asked viewers to weigh in on planning decisions about housing, transportation, the environment, poverty, and cities and suburbs.

In 1973, the RPA published a study demonstrating the link between higher urban density and lower per capita energy consumption during the oil crisis.

They also published a report advocating for pedestrian needs, including wider sidewalks, closing selected streets to vehicles, and pedestrian-friendly building design.

In 1999, the RPA was tasked by CSX Transportation with how to reuse the High Line, which was eventually decided on being a recreational trail, later implemented during the 2000s-2010s.

In 2007, the RPA advocated for the conversion of the James A. Farley Post Office into a transportation hub, which was later completed in 2021 as Moynihan Train Hall.

In 2010, the RPA supported the Access to the Region's Core (ARC) project, which would have increased rail capacity under the Hudson River.

In 2006, the RPA helped Newark craft a long term Draft Vision Plan for economic development, housing, environmental, and transportation improvements in the city.

Starting in 2014 in Suffolk County, the RPA helped plan out transit-oriented developments and walkable neighborhoods in Amityville, West Babylon, and the Hauppauge Industrial Park.

In 2004, the New Jersey Highlands Water Protection and Planning Act and the federal Highlands Conservation Act led to the preservation of nearly a million acres of environmentally sensitive land and protected a source of clean drinking water for more than 5 million New Jersey residents.

In 2013, the RPA, along with the National Park Service, helped improve access to the Jamaica Bay Greenway and waterfront.

In 2012, following Hurricane Sandy, the RPA launched scenario plans for the rebuilding of the region, which included a framework on how to reconstruct damaged and destroyed property for future community resilience.

A 2016 report called "Under Water" identified areas in the region at most risk for being permanently flooded by sea level rise.

[3] In 2017, the Fourth Regional Plan was created, which sought to address various issues including housing affordability, overburdened transit infrastructure, and climate change vulnerabilities.

Regarding equity, the plan sought to make land use decisions more inclusively; reduce inequality by expanding access to economic opportunity; invest in transportation and lower costs for those with the least ability to pay; and create sustainability through community outreach.

In 2018, the RPA advocated for the Meadowlands to become a climate resilience park due to the encroaching threat of sea level rise.

This included transit and bikeway improvements for workers, developing more affordable housing options, and countering misinformation.