Research on long-distance and interregional passenger mobility is an understudied class of travel that accounts for more than 2.6 billion annual trips by private vehicle, rail, air, and intercity bus. Interregional mobility is becoming increasingly important as travel demand changes and infrastructure condition and funding become more critical. Despite these factors, transportation research has predominantly focused on shorter-distance metropolitan travel. However, access to intercity travel impacts quality of life and long distance modes contribute significantly to environmental impacts. The relative lack of travel behavior data has limited investigation of this portion of the transportation system. This white paper reviews the history of long-distance travel in the United States, gives an overview of the data available for study of such travel including international data sources, and outlines what is known in terms of who travels how much for what purpose in a portion of the national multimodal transportation system. The white paper suggests utilizing a common framework for long-distance data collection and tabulation that re-defines long-distance travel.