The Brokaws said they were in the far left lane when they noticed a spool of cable bouncing along the far right lane. Just then, according to the Brokaws, a green SUV in the right lane came up fast and tried to avoid the cable.
The driver lost control of her vehicle and slid into the middle lane, forcing a mail truck into the Brokaw's lane of traffic.
Police said the 1998 Ford Expedition had collided with the US Postal truck. The SUV overturned ejecting driver, 30-year-old Suejas Estrada of the Bronx. She was thrown over the railing and down into a rail yard more than 70 feet below.
The 54-year-old driver of the mail truck was taken to Westchester Medical Center with bumps and bruises. He was listed in stable condition. His name has not been released.
Peter Rendina, public information officer from the U.S. Postal Service, also said the accident occurred when the SUV swerved to avoid a spool of wire that had fallen off the back of a truck.
The spool slammed into the 7-ton mail truck's front and the back wheel, he said.
Police said that debris caused the accident, but investigators have not yet located the spool of wire.
As the mail truck careened into their lane, 69-year-old Tom Brokaw hit the brakes and skidded along the median. When the mail truck catapulted the median, the Brokaw vehicle slid into it.
Brokaw's car sustained minor damage. Brokaw waited at the crash scene until Postal inspectors arrived.
"According to our inspectors, Brokaw did nothing wrong -- just in the wrong place at the wrong time," Rendina said.
Tom and Meredith Brokaw were not injured. In a statement, they said they were "greatly saddened by this loss of life."
Brokaw retired as anchor of NBC Nightly News in 2004. He had been an anchor on that newscast since 1982.
Preliminarily, police said there is no criminality suspected, but the investigation into the accident is continuing.