State Police are investigating two separate fatal car crashes, one in Watertown where a man slammed into a tree, and one in Andover where two people were ejected from their vehicles.

In the Watertown crash, Timothy R. Young, 22, of Brighton, was pronounced dead after his car went off the road and crashed into a tree, State Police said. State Police troopers responded to the crash on Nonantum Road at 2:05 a.m., State Police said in a statement.

Young was transported to Beth Israel Deaconess Medical Center in Boston where he was pronounced dead, the statement said.

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He was not wearing a seat belt at the time of the crash, said State Police spokesman David Procopio.

The cause of the crash is still under investigation, but excessive speed is a potential factor, State Police said.

In the Andover incident, two people were ejected from their cars and one died in a crash in the passing lane of Interstate 93, State Police said.

At 3 a.m. today, a 2009 Honda Fit was traveling north on I-93 and switched from the middle to left lane to avoid a slower vehicle. The Honda crashed into the median guardrail and its operator, 27-year-old Eoin Collins-Lyman of Tewksbury, was ejected from the car, State Police said.

A 2005 Land Rover that was traveling in the left lane struck the Honda. The driver, 40-year-old David L. Vaughan of Andover, was also ejected from his vehicle and pronounced dead at the scene, the statement said.

Collins-Lyman was treated for head injuries and transported to Lawrence Hospital. He was issued a citation by State Police for speeding, a marked lanes violation, and driving to endanger, the statement said.

It is not known if the drivers were wearing seat belts, State Police said. A reconstruction of the crash should help police determine if they were wearing seat belts or were not, Procopio said.

The crash remains under investigation.