Ridership on OC Transpo has dropped 70 to 90 per cent since the adoption of physical distancing and self-isolation measures to slow the spread of COVID-19, according to a memo sent to Ottawa city council Tuesday.

The drop has led OC Transpo to start rolling out services changes to the transit system beginning this week, said John Manconi, the general manager for transportation services, in the memo to council.

"With reduced ridership and COVID-19 potential impacts to the workforce, an adjustment to our multi-modal transit system is required to sustain and continue to provide the service while at the same time ensuring levels of service that enable social distancing," said Manconi.

OC Transpo starts reducing service on conventional buses and the O-Train in the coming days. It is also changing how it delivers Para Transpo.

Transit services in Gatineau, Que., and Kingston, Ont., are also cutting back.

Mayor Jim Watson supports the idea of keeping OC Transpo running during the pandemic so essential workers — like those who staff grocery stores and pharmacies — can still get to work.

"The reality is we need public transit even though our numbers are down substantially," he told CBC's Ottawa Morning Tuesday. "To shut that lifeline down would be a mistake."

For auto-renew monthly pass holders, Manconi says Metrolinx is giving riders until Friday at 11:59 p.m. to cancel their passes.

Starting Tuesday, March 24, most trips will be operated with only one customer on board to allow for physical distancing. Service levels will be managed according to demand and trip requests made a day in advance are still being accommodated.

Beginning Wednesday, March 25, trains will start arriving every 15 minutes. The area closest to the driver will be blocked off, similar to how it is on the Confederation Line. Stop and start times remain the same.

As of Friday, March 27, trains will arrive every six to eight minutes during peak hours and every 10 to 16 minutes on off-peak hours and weekends. Staffing levels at stations will be reduced. Stop and start times will remain the same except on early Saturday mornings when an overnight bus will take over from the train at 1 a.m.

Bus service will continue to be provided to all neighbourhoods but starting Monday, March 30, weekday service will move to a Saturday schedule on many routes. Rural weekly shopper services will continue as usual. The first trip in the morning will arrive later than normal on many routes. Saturday and Sunday service will run as usual.

The Société de transport de l'Outaouais (STO) is sharing lists of cancelled routes daily on social media.

Kingston Transit, which had already been running Saturday levels of service six days a week, will run Sunday levels of service all week starting Thursday, March 26.

All express routes will run once an hour from 8 a.m. to 8 p.m.

Riders are asked to take Kingston Transit only when it's absolutely essential.