The scope of Congestion Pricing was decided to fall under NEPA, the National Environmental Policy Act, and the government eventually decided that an EA was necessary. With NEPA, you must perform a study to create what is called an Environmental Assessment (EA) or, in the most stringent cases, an Environmental Impact Statement. These studies qualify and quantify what impacts, if any, your project has on various aspects of the environment and population. You submit your study and then await a decision, the end goal being a FONSI, or "finding of no significant impact" which will allow you to proceed with your project. They can be quite extensive and costly to perform, often at thousands of pages in length with up to 20 appendices. EAs and EIS are quite common for major projects and developments, NYC has its own processes related to NEPA, called CEQR: City Environmental Quality Review, as well as a state version called SEQR (State Environmental Quality Review).

You can read more about NEPA here: https://www.epa.gov/nepa
CEQR: https://www.nyc.gov/site/oec/environmental-quality-review/ceqr-basics.page
CEQR process: https://www.nyc.gov/site/planning/applicants/environmental-review-process.page
SEQR: https://www.dec.ny.gov/permits/357.html