OP is doing a bit, but it’s because a volume (liters) divided by a distance (km) reduces to an area. You can think of it as the cross-sectional area of a hypot

OP is doing a bit, but it’s because a volume (liters) divided by a distance (km) reduces to an area. You can think of it as the cross-sectional area of a hypothetical straw sucking up fuel from a continuous trough set into the roadway.