A Glut of Buses at the Crossroads of the World.

AT the Manhattan Plaza Health Club, on West 43rd Street near 10th Avenue, members often discuss the peculiar challenges of living in a neighborhood that also happens to be the crossroads of the world. But lately, the chats on the treadmills have focused on one particular issue: the swelling ranks of private buses and vans that pick up passengers in the area -- not from the Port Authority Bus Terminal, on Eighth Avenue, but from the streets nearby. ''They're everywhere,'' said Piper Smith, an illustrators' agent who is a regular at the club. ''They seem to be reproducing as we speak.'' [ABSTRACT FROM PUBLISHER]