Northwest Greater Toronto Area sub-region


The regional planning cycle for the Northwest Greater Toronto Area (GTA) sub-region was completed in April 2015 and an Integrated Regional Resource Plan (IRRP) was released.

Community Engagement

The IESO engages with local and regional communities to seek input to help inform regional planning activities. An Integrated Regional Resource Plan (IRRP) from the latest NWGTA planning cycle was finalized in 2015. See engagement materials on the previous planning cycle.

Regional Planning Status

The IRRP identifies several pockets in the study area that are currently at risk for not meeting targeted restoration levels during a system event. Two new step-down transmission facilities are recommended in the near term to ensure new customer connections can be accommodated in the Halton Hills and Milton service territories.

Over the medium term, or five to 10 years from now, a transmission line upgrade is recommended to address emerging capacity needs in the central Brampton area.

In the long term, 10 to 20 years from now, a need was identified to provide additional transformer and transmission line capacity in Northern Brampton/Southern Caledon and Halton Hills to meet forecast demand growth. An opportunity exists to cost effectively supply this long term growth by initiating approvals for the required transmission right of way in the vicinity of the planned GTA West Transportation Corridor.

The IESO and the Ministry of Transportation have announced a joint corridor identification study on a proposed land corridor in the Northwest Greater Toronto Area (NW GTA). The purpose of this study is to identify land to be protected for future multi-purpose linear infrastructure (such as transmission lines and transportation infrastructure) to ensure it can be accommodated if and when the need arises. The anticipated long-term need for new transmission in the NW GTA has been documented by the IESO through submission to official plans and the regional planning process, and has been highlighted in the 2017 Long-Term Energy Plan. Although the area of study is primarily centred in the GTA West planning region, parts extend into GTA North. The study will be conducted in phases and is expected to be complete within nine to 12 months. For further information, please visit the website for the study at

Additionally, a bulk system study is underway for GTA West to address anticipated overloads on major bulk system assets resulting from changing provincial generation and electrical demand patterns. The coordination of bulk system planning with the Integrated Regional Resource Planning process presents opportunities for potential solutions to meet both the bulk system needs and the local regional needs.

IRRP Working Group - Next Steps

A Working Group consisting of the local distribution companies in the region, the local transmitter and the IESO will use the regional planning process to identify and meet local electricity needs. Subscribe to receive GTA West updates on the status of the plan and to learn about opportunities for municipalities, community groups, stakeholders and the general public to provide input.

The working group consists of staff from Alectra Utilities, Halton Hills Hydro, Milton Hydro, Hydro One Networks Inc., and the IESO.

Area Overview

The Northwest Greater Toronto Area is defined in geographic terms as roughly the municipalities of Brampton, Milton, Halton Hills, and southern Caledon. The population of this area is over 700,000 and currently has a peak demand of approximately 1,200 MW. At two per cent per year over the past 10 years, historical load growth within this area is amongst the highest in Ontario.

The northern sections of GTA West are the focus of this IRRP due to a combination of high load growth, expanding urban boundaries, limited existing electrical infrastructure, and the requirement for coordination with bulk system plans impacting the sub-region.

Historical Context

As part of managing load growth over the past decade, several new system investments have been made, including new transmission lines and station and equipment enhancements, and the new Hurontario Switching Station. These measures have successfully enabled the area to meet the demands of the past decade, but continued robust growth is now driving the need for further investigation.