With 12,500 residents, NYU has the seventh largest university housing system in the U.S. and the largest among private schools. Uniquely, many of NYU residence halls are converted apartment complexes or old hotels. Most freshman residence halls are in the Washington Square area. While nearly all the upper classmen dorms are in the Union Square area, a few of them are as far as the Financial District, Manhattan. Until the Spring 2005 semester, NYU used a lottery system to determine eligibility for residence hall preference. Under this system, a student received one point for every semester they had lived in campus housing. Freshmen are freed from the lottery system and are by tradition placed in the halls closest to the main campus area. Therefore, historically, most of the students who lived in dorms found off-campus were sophomores. However, beginning in the fall 2006 semester, sophomores received priority housing, giving them first choice of residence halls. The purpose of this initiative was to keep the sophomore class together in the Union Square area. As a result, the junior class (class of 2008) and the senior class (class of 2007) never benefited from first choice as sophomores or seniors. The university operates its own transit system to transport its students, by bus or trolley, to campus. Undergraduate students are guaranteed housing during their enrollment at NYU.