Recently, I was involved in a minor car accident. When my car stopped at the traffic light, I switched on my left signal light to show my intention to change to left lane. At the same time, I notice a car stop behind me also switching on the left signal light. When I was coming out, the car suddenly sped up and came out at the same time, so we hit each other. My left front wheel and his right back door also have minor damages. I would like to ask who is at fault?