With its hub at Union Station in Toronto, GO Transit's green-and-white trains and buses serve a population of more than seven million across an area over 11,000 square kilometres (4,200 sq mi) stretching from Kitchener in the west to Peterborough in the east, and from Barrie in the north to Niagara Falls in the south.

Today, it is an operating division of Metrolinx, a provincial Crown agency with overall responsibility for integrative transportation planning within the Greater Toronto and Hamilton Area[7] and is projected to grow dramatically with electrification, increased frequency and new stations through the GO Expansion, which is scheduled to be completed in phases through 2025–2032.

[8] Cities in and around the Greater Toronto and Hamilton Area (GTHA) expanded greatly during the 1950s, influenced by growth in immigration and industrialization.

The idea of GO Transit was created out of fear of becoming lost in years of planning; it was "approached as a test, but recognized to be a permanent service".

[14] Other than establishing new rail corridors, GO Transit introduced the Bombardier BiLevel Coaches in 1979, in order to increase the number of passengers carried per train.

It eventually became a full-fledged network in its own right after 1989, feeding rail service and serving communities beyond the reach of existing trains.

[11][13][18] In a series of cost-cutting measures, then–Ontario Premier Bob Rae announced a "temporary" reduction in spending on services, causing all of the expansions of the 1990s to be reduced or eliminated.

However, then-Premier Mike Harris announced the province would re-assume funding responsibility for GO Transit two years later, and this was completed with the abolition of the Greater Toronto Services Board on January 1, 2002.

[23][24][25] The Greater Toronto Transportation Authority was created in 2006, with the responsibilities of co-ordinating, planning, financing and developing integrated transit in the GTHA.

GO Transit continued as an operating division alongside two other major initiatives: the Union Pearson Express and Presto card.

As part of the 2011 provincial election, Premier Dalton McGuinty made a campaign pledge to provide two-way, full-day train service on all corridors.

Part of Metrolinx's Big Move regional transportation plan, it is estimated to cost $4.9 billion and serve 30 million additional riders by 2031.

[27] Other possible future rail service extensions identified in GO Transit's 2020 plan include Niagara Region, Bolton, Brantford, Peterborough and Uxbridge.

The 10-year regional express rail plan will cost $13.5 billion[38] and will require 150 kilometres (93 mi) of new track, including new bridges and tunnels.

[39] Starting January 1, 2025, the consortium ONxpress will take over the operation and maintenance from Alstom of the GO Transit train system in addition to introducing the improvements required for GO Expansion.

GO Transit's lines extend into the nearby Niagara and Waterloo Regions, the cities of Brantford and Peterborough, and Simcoe, Dufferin and Wellington counties[1]—an area largely coextensive with the Greater Golden Horseshoe.

Present extrema are Brantford and Kitchener to the west; Orangeville, Barrie to the north; Peterborough and Newcastle to the east; and Niagara Falls to the south.

Until 2012, five GO Train lines operated only during weekday rush hour periods in the peak direction (inbound towards Union Station in the morning and outbound in the afternoons and early evenings), with off-peak service on these routes being provided solely by buses.

Its passenger car fleet is composed entirely of Bombardier BiLevel Coaches built in Thunder Bay, Ontario.

[46] GO Transit built a second maintenance facility covering 500,000 square feet (4.6 hectares) in Whitby to accommodate additional trains for its upcoming Regional Express Rail project, and was completed by the end of 2017.

In April 2008, GO began operating 43-foot (13.11 m) Enviro 500 double-decker buses built by British manufacturer Alexander Dennis in the United Kingdom.

The lower height allows these buses to meet many more clearance standards as a result and are used on a wider variety of routes, including those that travel on Highway 401.

Despite the lower height, these buses are still too high to fit in a number of GO terminals, namely Hamilton, Yorkdale, York Mills, and Union Station.

[67] The Presto card, available on all GO trains and buses,[68] is a unified smart card-based payment system used throughout the Greater Toronto and Hamilton Area.

Passengers are required to carry a valid GO paper or digital ticket or pass, a tapped-in credit/debit card/mobile wallet or Presto card to prove that they paid for their fares.

2 is a document of rules and regulations governing actions of passengers and employees while on GO Transit property, which includes land, facilities, trains, buses and other structures.

[83] On December 12, 1975, a westbound GO train collided with a Toronto Transit Commission (TTC) bus that was stalled on a crossing at St. Clair and Midland Avenue.

The two trains then collided at a speed of 19 km/h (12 mph), causing a partial derailment and minor injuries to fifty-four passengers and two crew members.

The subsequent Transportation Safety Board report made recommendations, including making emergency brakes more accessible and that the locomotive engineer must always control the train from the leading end in the Union Station Rail Corridor.

[87] On July 8, 2013, a Richmond Hill–bound GO train encountered flash flooding in the Don Valley when a record-breaking 123 mm rain storm fell over a few hours in Toronto area.