The victim, whose name has not been released, was hit by a northbound train at the East Meadow Drive crossing shortly after 8:20 a.m., Caltrain spokeswoman Christine Dunn said.

The gates at the crossing were down, and the lights and bells were working normally, Dunn said.

"He went around the gates and walked onto the railroad tracks in front of an express train," Dunn said.

Why the teen did that is unclear, she said.

"It's impossible to say what's in the mind of a person in this situation," Dunn said. "It's difficult to make a decision about whether the behavior is random recklessness, inattention or whether it was intentional."

The boy was hit about a mile north of where a woman was struck and killed by a Caltrain on Monday. Authorities said the woman, Heather Lynn Russell, 29, of Palo Alto, sat down on the tracks in an apparent suicide.

E-mail John Coté at jcote@sfchronicle.com.

This article appeared on page B - 7 of the San Francisco Chronicle