There are several reasons for not bothering with the door. Immediately upon impact, you have only a few seconds in which opening the door of your sinking car is possible, while most of the door is still above water level. Once the car has started to sink, it is not humanly possible to open the door again until the pressure between the inside and the outside of the car has been equalized (leveled); this means that the car cabin has to be filled with water and that's not really a state you want to be in.
最好不要开车门，原因如下：面对突然遭受的冲击，正在入水的汽车只给你提供几秒钟的时间来打开车门逃生，也就是当车门还在水面上的时候。一旦汽车开始下沉，由于汽车内外的水压相等，靠人力是根本无法打开车门的。这也就意味着车厢开始充满了水，你已经完全不会想继续呆在里面。
The end of the car that contains the engine will usually sink fastest, often leaving the car at an angle where the heaviest part of the vehicle is lower than the lightest. As such, you may be able to open some doors while the car is still floating.
由于发动机的原因，汽车尾部往往是下沉最快的，通常会使汽车达到一个角度，最重的部分比最轻的部分位置低。所以当车子还在漂浮的时候，你有可能打开车门逃生。