Regional transit agency TriMet this afternoon issued an extraordinary plea to Portlanders: Please don't ride trains or buses unless you have to.

"Please only take transit if necessary and maintain 6 feet of distance from other people and the operator if you do ride," the agency said in a statement.

The request follows an order by Gov. Kate Brown this morning that Oregonians stay home except for exercise, necessary work, and urgent trips like grocery shopping and medical appointments. The governor's shutdown of most public spaces is intended to stop the spread of the COVID-19 coronavirus.

Few places are as high risk for virus transmission as a train car. So TriMet asks that public transit be reserved for riders who have no other choice.

"Our buses and trains are running to transport medical staff, first responders and other essential workers where they need to go," the announcement says. "By avoiding unnecessary trips, you're helping give them the space they need to ride safely."

Many Portlanders won't need the encouragement: TriMet says its daily ridership fell by 140,000 last week. That's a 58 percent drop in daily transit trips.