CRESCENT CITY, Fla. -- The engineer of the Amtrak train that crashed near this hamlet told investigators he threw on the emergency brakes just before the deadly derailment because he saw misaligned tracks ahead, the NTSB said Friday.

More than half of the Auto Train's 40 cars skidded off the tracks Thursday. Four people were killed and more than 150 injured.

George Black of the National Transportation Safety Board said investigators have not yet determined what caused the train to hurtle off the tracks. He said investigators were still trying to confirm whether the track was out of alignment.

The tracks had been visually inspected eight hours before the crash and had been in good condition, according to CSX, the freight railroad that owns the track. A National Railroad Administration inspection last week and two other inspections in the past six months turned up no problems.

It is not uncommon for rails to expand in the Florida heat, but Black said the temperature -- 81 degrees -- did not appear to be a factor. Misalignments can also be caused by damage done by a previous train.

Black said four other trains had passed over the area just before the wreck, apparently without trouble. He said investigators examined two of those trains for signs of damage from bad track and found none.

Amtrak spokeswoman Cheryl Jackson said sabotage was not suspected.

The engineer, who was not hurt, was tested for drugs, a routine step after an accident. The results were not immediately disclosed. The engineer's name and background were not released.

The train, which carries both passengers and cars and is a favorite among tourists traveling between Washington and Orlando's theme parks, was going 56 mph in a 60 mph zone when the accident happened, Black said.

Death toll changes

The death toll was reported at six Thursday but was revised Friday by investigators and medical officials. In all, 166 passengers were taken to hospitals. Twelve remained hospitalized, including a 73-year-old woman in critical condition.

The names of the dead were not immediately released but they were described by medical examiners as a 75-year-old man, a 67-year-old man, a 64-year-old woman and an elderly woman. Hometowns were not provided.

Sharon Mahoney, the 52-year-old general manager of the Auto Train service, was on the train at the time. She was not injured, and helped direct the rescue efforts.

Mahoney was riding in the first passenger car, a sleeper that did not leave the tracks. "I was just thrown about in my chair. We trembled for about 60 seconds. I could hear the squeal of the brakes," she told The Associated Press.

When passengers and crew were taken to a high school, she rode the bus with them. "I needed to be there with our guests and crew," she said.

The Auto Train was bound for Washington with 418 passengers and 34 crew members, and 200 automobiles stacked in 23 specially designed cars.

The accident happened about an hour into the trip. The two engines and first two cars stayed on the track, but 14 of the 16 passenger cars and seven others derailed in the remote, heavily wooded area 60 miles north of Orlando.

There were selfless acts of heroism as those aboard helped each other escape the overturned cars. Amtrak chef Harry Gissendanner was credited with helping passengers out of the dining car despite burns on his hands and legs.

Using ladders to reach the overturned cars, rescuers helped survivors out of the train and reached through shattered windows to get to those still trapped inside.