A seat is not a journey: comparing transport on the same unit

Transport comparisons can fail when vehicle-kilometres, passenger-kilometres, seating capacity, and complete journeys are treated as interchangeable. This methods note develops an event-travel comparison using the UK government’s conversion-factor methodology and GHG Protocol product and policy-accounting standards. A fictional twelve-person case illustrates occupancy, detours, positioning, and the risk of rewarding unnecessary distance through a denominator. The analysis distinguishes factors that already contain occupancy assumptions, aligned operating boundaries, average allocation, and marginal consequences. Accessibility and a feasible return journey define the service rather than appearing as optional extras. No real emissions or modal savings are calculated. The resulting record supports comparison of complete, usable journeys while retaining uncertainty about vehicles, routes, factors, and displaced alternatives.