If an accident can be avoided, it should be avoided. In this manner, the trucker is theoretically partially in the wrong, but the car is still at fault. However, it can easily be argued that honking your horn should avoid any further incident. With most people, it's easy to imagine why slowing down would be preferred, however with trucks unnecessary braking will only consume more fuel. It can even be argued that the trucker braking could cause traffic disruptions behind him, putting even more at risk. Even so, the car didn't really slow down (if at all) until he was in front of the truck. It's perfectly reasonable to believe the car would have kept his current speed or accelerated more after merging. After thinking about it more, and typing it out. Car is 100% at fault.