NEW YORK - (AP) Federal authorities have issued an emergency order instructing the Metro-North Railroad to modify its signal system. It's also been ordered to put extra operators on lines where there are major speed changes, like the curve where a passenger train derailed earlier in the week.

The order said immediate changes were needed to make sure train crews don't exceed speed limits.

A commuter train went off the tracks Sunday after an engineer hit a curve at nearly three times the 30 mph speed limit.

The train operator told investigators he fell into a trance, or nodded off, at the controls.

The Metropolitan Transportation Authority, which oversees Metro-North, said it would comply with the order.

It said it also examining other steps to improve safety following the crash, which killed four people.