Yes, it is correct. I am familiar with the cameras used for vehicle detection, having worked with them before. They are fixed in place and designed to view an entire leg of an intersection. They can zoom in and out, but they do NOT have the zoom capabilities required to do what you say. Even if they did, zooming into a portion of the view would screw up their detection capabilities, because to configure them you must define the detection zones and once that is done they must be reset if the camera zoom is changed. So the camera is zoomed to show enough of the intersection where detection zones are to be configured, they are configured, and then the camera is never changed again unless it's desired to reconfigure the detection zones.
The ptz cameras (in the dome enclosure) DO have the ability to zoom, but they are not generally used that way unless a human operator sees something of interest and manually commands the camera to zoom into an area. Otherwise, they are left zoomed out.