Travel fatigue is temporary exhaustion and follows any long journey, including car-, bus- and train trips. It follows a period of prolonged inactivity, irregular sleep, restricted food choices, dehydration, and other factors that are associated with long-distance travel.
Jet lag, on the other hand, while also temporary, follows rapid long-distance travel crossing three or more time zones. It is caused by the fact that your body clock is out of sync with the time zone at your new destination.