A Transit Project Assessment Process (TPAP) for the Relief Line South Project was carried out in 2018. The TPAP is an environmental assessment process developed specifically for the approval of public transit projects. The Transit Projects Regulation, Ontario Environmental Assessment Act, Regulation 231/08, exempts proponents of all public transit projects from the requirements under Part II and Part II.1 of the Environmental Assessment Act, and creates a process that certain projects must follow in order to be exempt. The TPAP is a proponent-driven, self-assessment process and does not require that a transit project be approved by the Minister of the Environment, Conservation and Parks before proceeding.

The Environmental Project Report (EPR) prepared for the Relief Line South Project documents the planning, consultation, and decision making process followed before and during the course of the TPAP. It provides a detailed description of the transit project and describes the existing and future conditions in the area. It also summarizes potential environmental effects that could occur with the implementation of the Relief Line South project. The EPR proposes mitigation measures and monitoring activities to address the documented environmental effects.