“…Graham and Glaister (2002) provided an update; but of the studies they cited, only four involved cointegration, 1 and none focused on the US. Likewise, the few studies since that review that employ conintegration have focused on countries other than the US, e.g., Brazil (Alves and Bueno, 2003), Greece (Polemis, 2006), Namibia (De Vita et al, 2006), and South Africa (Akinboade et al, 2008). Furthermore, only one previous cointegration analysis estimated a genuine long-run relationship: Bentzen (1994) As noted, spatial intensity influences transport demand; however, since the area of the US has remained constant over the period studied (albeit, US territories Alaska and Hawaii became states in 1959), population density simply increases with increases in population, and thus, is not an appropriate variable for a time series study like this one.…”