Source: adapted from Schafer, A. (2000) Regularities in Travel Demand: An International Perspective, Journal of Transport Statistics, Vol. 3, No. 3.
Distance remains a significant factor in the modal choice of passengers. The above figure underlines two thresholds. The first being the 30 minutes walking threshold, representing about 2-3 kilometers beyond which the average person is unwilling to walk. However, in a motorized society such as the United States, the automobile plays a significant role in short distances. This is associated with the urban physical setting, which is less suitable for walking; lower densities, fewer sidewalks. The second is the 1-day driving threshold, at about 700-800 kilometers. Beyond this point, air transportation clearly dominates and becomes the only possible mode for distances of more than 8,000 kilometers.