Metrolinx says it will increase service in September on GO Transit routes as part of the reopening of Ontario.
The company says the changes on its rail and bus lines are the most significant in its history.
Metrolinx says service will change on most of its routes as schools and workplaces reopen.
It says there is an increasing number of customers returning to transit.
Returning riders will see changes, including mandatory face masks while in transit.
Metrolinx says it has also installed new wayfinding signs and seat dividers on many vehicles to provide more protection while travelling.