A Quincy motorist plowed into a pedestrian crossing Massachusetts Avenue in front of the Orange Line station around 6 a.m., then just drove away, police say.
The victims remains in critical condition at a local hospital, the Suffolk County District Attorney's office reports.
Lawrence Stead, 69, of Quincy, was arrested later in the morning in Quincy, after police traced the license-plate number of the gray, 1999 Mercury Marquis seen leaving the scene to his home.
Stead is scheduled for arraignment tomorrow in Boston Municipal Court on a charge of leaving the scene of a personal-injury accident, the DA's office reports.
WBZ reports Stead is a retired Cambridge cop.
Massachusetts Avenue was shut for much of the morning as police investigated the crash.