The pair of newly installed signs prohibit motorists from turning left from the north-facing campus exits onto westbound Mast Boulevard.
West Hills junior Ryan Willweber, 17, was trying to make that maneuver when his car was struck broadside by an eastbound SUV the afternoon of April 30.
He died in a hospital a short time later. His younger brother, who was riding alongside him at the time of the accident, suffered serious but non-fatal injuries.
To accommodate drivers who need to go west on Mast Boulevard from the school, traffic engineers adjusted a traffic signal at Medina Drive to facilitate U-turns.
Additionally, roadway striping on the street will be reconfigured in both directions to create a buffer zone between traffic lanes and bicycle paths, according to Santee City Manager Pedro Orso-Delgado.
The city also is working with a developer to install a traffic signal at the western entrance to the high school before the September start of the upcoming school year, officials said.
Pardee Homes has agreed to pay for the lights ahead of completion of the company's Castlerock residential development, to be situated on 203 acres across the street from the campus.