The Greenbelt Training Races found here:
http://www.route1velo.com/GreenbeltInfo.asp
..are semi-closed. It has a Brit-lane (I made that up, but it's a lane that motor vehicles drive on the "wrong" side of the road, but in the same direction that the racers are going (clockwise around the park). The center line rule and all USCF rules apply.
Here's some text about the course (2007 permit):
Course / Format
The course loop is approximately 1.4 miles on the perimeter roadway of the Park. The yellow line rule is strictly enforced. The race start times and distances may vary depending upon safe racing conditions and the Chief Referee and/or Park Rangers' discretion.
The race format may change with approval of both the promoter and USCF Oficials. The race will be held unless course conditions are deemed unsafe by the promoter, Chief Referee and/or Park Rangers.
Note: if rain is forecast for Wednesday afternoon or evening, advance notice of race cancellations may be made by 4pm that day. Use the contact information listed below for status updates.
All USCF rules apply. Held under USCF permit 2007-875.
The point? Not all USCF crit races are blessed with completely closed courses or devoid of the center line rule.