Heavy snowfall and “deteriorating conditions” led Pittsburgh Regional Transit to suspend all bus and rail service in the region Sunday at around 5 p.m., the transit agency posted to social media.

Normal operations are expected to resume Monday morning.

In Westmoreland County, all fixed-route bus service from Westmoreland Transit is suspended on Monday until at least noon. All Pittsburgh Flyer services are canceled for both the morning and afternoon.

On Friday, Westmoreland Transit announced restrictions on some lines on Monday: Route 1F and Route 4 will not service Adamsburg; Route 5 will not service Altman Road area; Route 16 will not service Hecla.

For PRT, the Downtown Service Center will be closed Monday. Riders may reach customer service representatives, however, by phone and through the agency’s website.

The announcement came as road conditions hobbled public transit in Allegheny County through much of Sunday.

Several buses remained stuck in the snow around 5 p.m., according to CEO Katharine Kelleman.

“Our operators deserve to be commended for doing their best under very challenging conditions, but the situation has deteriorated to the point where continuing service could put both our operators and riders at risk,” Kelleman said in a prepared statement.

“With several buses already stuck in the snow,” she added, “we must err on the side of caution and safety.”

On Sunday evening, PRT announced that ACCESS paratransit services are canceled Monday. Earlier in the day, PRT said it hoped to run ACCESS on Monday, with delays.

During the day Sunday, some PRT bus services had been delayed up to an hour and several routes were not able to run at all, including:

• 6-Spring Hill, 15-Charles and 17-Shadeland in Pittsburgh’s North Side

• 74-Homewood-Squirrel Hill in parts of the city’s Homewood neighborhood

• P68-Braddock Hills Flyer and the Braddock Hills Shopping Center.