The driver of a grey Nissan Altima collided with a Lincoln sedan this morning around 12:17 a.m. The accident occurred in the northbound lanes of I-15 just south of the Carmel Mountain Road exit. Four people were injured and were transported to Palomar Medical Center in unknown condition. The cause of the accident is still under investigation. It is also unknown if alcohol and or drugs were a factor. Contact CHP San Diego for additional details.