In CA, it depends entirely on the sherrif in the county in which one lives. In most areas, it is next to impossible. In more rural counties, it isn't hard at all, although it often requires demonstrating range proficiency with each gun you want to list on your permit. Legality of concealed carry aside, there is a real problem with pulling a gun in traffic. You are only allowed to pull a gun if a jury of your peers would agree that you had a reasonable fear of mortal danger. Some states also require that you make an effort to retreat and I don't know if CA is one of those states or not. Even without the "duty to retreat", there is a tactical problem in that when you stop to pull your gun, the threat has likely continued driving on. You can not pursue that threat and still be viewed as a victim. Shooting while moving has other legal implications since you are responsible for the destination of each one of your shots. Whether on a bike or in a car, you have better tactical and legal options than firing to or from a moving vehicle.