Auto Insurance Claims: Rear Ended, rear end collision

Question
Hello:
I rear ended someone but here is the situation. I was next to HOV lane and the HOV lane was separated by double yellow line. The distance between my car and the car infront me was like 5-6 cars but suddenly this cars from HOV lane entered into my lane from left without giving any indication and by crossing a double yellow line and stopped because of traffic. So is it my fault? No witness its his word my word and maybe this guy will deny this.

Answer
Without witnesses or other proof, a car that rear ended another car is usually 100% at fault. That's just how it works in the courts and insurance claims. But go ahead and make your argument, maybe you can get some lower percentage of fault. Go back to the accident scene and get photos.