in the driver's seat is to be in a position of authority or in a position where one can control events.
在驾驶员的座位上：是指处在权威地位或在处在一个可以掌控事件的位置。
Now that her manager’s on vacation, Sally is in the driver’s seat and must make all the important decisions

现在她的经理正在休假，萨利处在驾驶员的位置上，而且必须作出所有重要决定