Here is the link to the roundabout brochure.
http://www.districtgov.org/community...t-02-08-12.pdf
The third bullet point quite clearly states "Do not change lanes in a roundabout"
Navigating Roundabouts
• Move up to the entrance line and wait for a gap in traffic. DO NOT ENTER next to a vehicle in the round- about, as that vehicle may be exiting at the next exit.
• Within the roundabout, do not stop except to avoid a collision; you have the right-of-way over entering traffic. Keep moving in a counterclockwise direction.
• Do not change lanes in a roundabout.
• A striped channelization island is present in several
roundabouts, which reduces the circulatory roadway to one lane approaching a single-lane exit.