Final answer:
Changing lanes without signaling is not considered safe driving on an interstate. Signaling allows other drivers to anticipate your actions and respond to avoid accidents. Slower traffic should stay to the right, and if an exit is missed, one should proceed to the next exit safely.
Step-by-step explanation:
The action that is not considered safe driving on an interstate system is changing lanes without signaling. This is because signaling is a critical part of safe driving; it communicates your intentions to other drivers and allows them to react and adjust their driving accordingly. Failing to signal can result in accidents due to sudden and unpredictable lane changes.
Other safe practices on an interstate include that slower traffic must keep to the right, and if you miss your exit, it's important to proceed to the next exit instead of attempting any abrupt and potentially unsafe maneuvers to correct the mistake. There is no context for option 4, 'cannot be fixed' in regard to safe driving practices on the interstate.