David "Spanky" Sousa, of Stoughton, was struck around 9:30 p.m. while working on the side of the northbound lane near Ext 28B, The Plymouth County District Attorney's Office said.
Sousa is a husband and father who has served as a former Stoughton Select Board chairman.
The driver who struck him remained at the scene, the prosecutor's office said. Their name was not released.
Authorities closed the road for three hours after the crash, as they cleaned, and cleared the scene. Officials are investigating the cause of the crash.
American flags on government buildings throughout Stoughton on Monday were lowered to half-staff in Sousa's honor.
Click here to follow Daily Voice Waltham and receive free news updates.