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, says it will comply with the order.
It said it also is examining other steps to improve safety following the crash, which killed four people.