5gc involved in bus accident in AL Options

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HUNTSVILLE, Alabama (CNN) -- A fourth teenage girl died Tuesday at a hospital from injuries sustained when a school bus plunged off a highway overpass Monday in Alabama, Huntsville Police Chief Rex Reynolds said.

She was identified as Crystal Renee McCrary, 17. The three others killed were Christine Collier, 18; Nicole Ford, 17; and Tanesha Hill, age unknown. Collier and Ford both died at the scene Monday, while Hill died hours later at Huntsville Hospital.

Fourteen students and the bus driver remain hospitalized, including at least three in critical condition. (Watch how the crash has left the city in shock -- 1:40 )

National Transportation Safety Board investigators are on the scene trying to determine what caused the accident.

The bus, carrying 40 students from Huntsville's Lee High School, fell 30 feet to the street below an overpass on Interstate 565 and landed on its front end before flipping over.

The bus driver was either ejected or escaped from the vehicle before it fell, NTSB investigator Debbie Hersman said Tuesday. He was found on the overpass by rescue workers, she said.

The initial investigation indicated that a small sedan driven by a fellow high school student veered into the bus' lane, causing the bus to drag along the concrete barrier for more than 100 feet before plunging off the interstate overpass.

Police have interviewed the 17-year-old driver of the orange 1990 Toyota Celica as well as the bus driver.

They planned to interview the bus driver again on Tuesday, Huntsville police spokesman Wendell Johnson said.

According to Hersman, the teen driver told police something went wrong with the Celica that caused it to drift into the bus' lane. The NTSB is investigating whether the car struck the bus.

The car had two flat tires after the accident, although it was unclear when they went flat and what role that might have played.

Photos of the car on the overpass showed damage to the driver's side door and the front passenger side.

Police have not decided whether the teen driver will be charged. (Watch officials describe the bus crash -- 1:16 )

"Huntsville has never seen an accident like this involving students," said Johnson, the police spokesman.