Nicolas Svercel, 15, was riding northbound across the road.
According to witnesses, Helkin of Farmingdale had a green light as he drove westbound on Route 347 when Svercel started crossing the road.
Svercel had been riding with three other teenagers and he may have believed the light changed, allowing him to cross the roadway.
Svercel was pronounced dead at the scene by a physician assistant from the Office of the Suffolk County Medical Examiner.
The Mazda was impounded for a safety check, and the investigation is continuing.