Are domestic long-distance travel and international flying complementary? Evidence from England’s National Travel Survey, 2015–2019

Research on the demand and climate impacts of domestic and international long-distance travel (LDT) has expanded rapidly, yet comparatively little is known about whether these two domains are behaviourally interlinked; that is, whether participation in one is associated with participation in, or the intensity of, the other. This paper addresses that gap by examining the relationship between domestic LDT and international flying at both the extensive (participation) and intensive (frequency) margins within a common analytical framework. Using pooled National Travel Survey data for England (2015–2019), the study estimates zero-inflated negative binomial (ZINB) models of annual trips per person with cross-domain participation as a key explanatory variable and a control-function correction for potential endogeneity across both domains. Conditional mixed process (CMP) simultaneous-equation models provide a broader robustness check. Descriptively, among respondents aged 16 and above, those who had taken at least one international flight in the previous year (fliers) were substantially more mobile domestically than those who didn’t. Fliers travelled around 50 % further in total but nearly twice as far in domestic long-distance trips, generating proportionally higher emissions than non-fliers, suggesting the main divide lies in longer-distance rather than everyday travel. ZINB models show a positive bidirectional association between domestic LDT and international flying at the extensive margin, where participation in one domain is associated with a higher likelihood of participation in the other. At the intensive margin, however, the association becomes asymmetric, as international flying participation is not associated with higher LDT frequency among its participants. CMP models point to modest shared unobserved drivers of entry across both domains and identify another directional asymmetry, as domestic LDT frequency is not associated with international flying participation. Together these patterns indicate asymmetric co-variation rather than symmetric patterning and support treating domestic and international long-distance travel as interconnected components of individual mobility.