Conjugated polymers are attractive semiconductor materials because of their processability, chemical tunability, flexibility and biocompatibility, but are limited by poor charge-carrier mobilities. Surprisingly, some of the best performing polymers are non-crystalline, which makes it challenging to pinpoint the microstructural origin of their high mobilities. In this work, the nature of interchain π-system contacts, and their relationship to hole transport, are elucidated for the high-mobility, non-crystalline conjugated polymer C16‑IDTBT by the application of scanning tunneling microscopy, molecular dynamics, and quantum chemical calculations. The microstructure is shown to favor an unusual packing motif in which paired chains cross over one another at near-perpendicular angles. By linking to mesoscale microstructural features, revealed by coarse-grained molecular dynamics and previous studies, and performing simulations of charge transport, it is further demonstrated that the high mobility of C16-IDTBT can be explained by the promotion of a highly interconnected transport network, stemming from a combination of chain rigidity and the adoption of perpendicular contacts at the nanoscale.