Somewhat of a tactical error on your part. It's always advisable when in traffic to leave "maneuver" room by just stopping a little sooner and leave a car length in front. Even if you can't pull totally out, you can start moving and that may discourage someone on foot. It also keeps you from hitting the car in front of you if rear-ended yourself.
Plus 10,0000 this is my personal pet peeve about Seattle drivers and especially folks new to the art of saving your a$$.
You should be able to see the bottom of the rear tires of the vehicle in front of you at a minimum.
Also - drive or draw, not both. You are almost ALWAYS better off driving out than shooting it out.
I don't change my carry position when in the car. The more often you f**, er futz with your weapon the more likely you are to do something stupid and ventilate your car.