Metro suspended operations Sunday night on all routes and lines, as a result of hazardous road conditions, the transit agency said.
Metro said deteriorating conditions, including ice formation, have affected its ability to operate safely.
The transit agency said buses already on their routes would go to the end of the line before halting service.
It recommended that those who take the bus should use Metrorail if possible. Metrorail will continue normal service until its regular 11 p.m. closing, Metro said.
Metro said it would continue to monitor conditions, and would resume bus service when conditions improved, allowing safe operation.