The Federal Aviation Administration, acting after a series of deadly ground collisions, ordered air traffic controllers on Friday to tighten procedures for moving aircraft onto runways.

The FAA told controllers to stop authorizing aircraft to taxi at night onto a runway from an intersecting taxiway and wait there for further instructions.The practice will also be prohibited whenever the intersection cannot be seen from the control tower because of bad weather or an obstruction, the agency said.

Eight people were killed when two Northwest Airlines planes collided in heavy fog on a runway at Detroit on Dec. 3, and 32 died in a runway collision at night at Los Angeles on Feb. 1.

The FAA said the changes in handling aircraft on the ground are among several it has been considering in a review of airport procedures begun almost two years ago.

Last week the agency announced a $50 million national program to improve runway markings and to install modernized guidance systems to help controllers and flight crews.

The FAA told its controllers that "the increasing mix of traffic at airports requires changes."