Three Freehold High School students and a 68-year-old woman were killed in the accident. Police estimated the teens were traveling faster than 90 miles per hour before the crash.
Brennessel's car was not involved in the collision, but prosecutors argued the teen was speeding and driving recklessly.
State Superior Court Judge Anthony J. Mellaci Jr. overturned the municipal court convictions, finding Brennessel guilty of a lesser speeding offense.
He reduced Brennessel's two-year license suspension to six months and cut his sentence of 180 days' community service to 75 hours.