Vehicular tyre tread and footprint characteristics have been investigated from the point of view of tyre design and manufacturing and dynamic vehicle analysis, as well as for pavement design and analysis. From these analyses, it has become clear that typical commercial truck tyres do not exhibit a uniform pressure over the footprint area. Instead, a highly non-uniform pressure distribution is observed depending on tyre type, internal pressure, axle load, etc. Nevertheless, such analyses are generally related to rigid driving surfaces, but commercial vehicles also frequently cross bridges, where the driving surface is much more flexible. Indeed, the flexibility of a steel deck will change the footprint characteristics due to the adaptation of the contact surface to the presence of more and less rigid areas. In this paper, the pressure distribution under a truck tyre when crossing a bridge with a steel orthotropic bridge deck is investigated. The contact pressure is measured by an 8.4 mm-resolution pressure mat in between a common widebase tyre and an orthotropic bridge deck test specimen. Comparisons are made with existing literature for rigid surfaces, especially the analyses of R Blab at Berkeley, in order to investigate the influence of the tyre pressure, total applied load and the transverse position relative to the rib walls on the pressure distribution. The results indicate that the transverse positioning does indeed affect the pressure distribution, as the suffer rib wall attracts a larger part of the load. Consequently, uniform pressure loads overestimate plate bending for loads in between the rib walls and underestimate plate bending for loads over the rib walls. In this way, the detailed non-destructive pressure distribution analysis has contributed to a better understanding of failure analysis, especially at the rib-to-deckplate connection, of steel bridge decks.