This study informs the interface of travel demand analysis and health policy. There is a demand for cycling, walking or taking non-motorized modes together – a demand for ‘active travel’ – a term describing modes of transport which incur significant cardiovascular effort or metabolic costs. It is possible to establish a meaningful and policy relevant view of active travel demand by controlling for partially unobservable (not simply unobserved) generalized cost effects – where generalized cost can be considered the sum of all individual cost-components. Using monthly aggregated data from the UK National Travel Survey it is found that income effects are greater for lower income households and diminish with wealth and that some ‘seasonal substitution’, due to ‘generalized’ cost effects, can be identified. One consequence of this is that policy for active travel needs to be seasonally adaptive to reflect these substitution effects.