The Mini-Urban Challenge is a national competition sponsored by The Institute of Navigation and the United States Air Force Research Laboratory that challenges high school students to design and operate a robotic car to autonomously navigate a LEGO® city. The cars are developed using LEGO® MINDSTORMS® Education kits that are provided to high school teams free of charge.
For More Info see: http://www.ion.org/outreach/muc/
Only found out about this today, but the 2011 National Championships were on May 21, but it does seem to be a yearly event (2009-2011).