UPDATE Nov 10, 2009:
According to information received from a business near the construction area (who kindly provided this SHA Announcement) and my own observation this afternoon, apparently one or more lanes will be kept open during construction on that portion of Powder Mill Rd.
ROUTE 212 WIDENING: Work is scheduled to begin this week (Nov 9) on a $1.2M road widening project along a half mile of Route 212 on Powder Mill Road between Evans Trail Way/Allview Drive and Beltsville Drive in Beltsville.
Some Powder Mill Road lanes will be closed on weekdays between 9:00 AM to 3:00 PM and overnight Sundays through Thursdays from 9:00 PM to 500 AM. Construction is scheduled to last until next summer. (map) Dr. Gridlock, Washington Post Nov 8, 2009
(Thanks to Karen M.)