Metro passengers may find slight delays to service Saturday during an emergency drill on the Tempe Town Lake light rail bridge. Metro will stop a train on the bridge and evacuate volunteers with emergency personnel practicing a response. The drill is scheduled from about 9 a.m. to 11 a.m. During that time, only the eastbound sides of the stations at Priest Drive/Washington Street, Center Parkway/Washington Street, and Mill Avenue/Third Street will be active.