1. A method, comprising: receiving a video image of a road surface imaged and of a vehicle moving across the road surface; determining a tracking point of a vehicle image, of the vehicle, captured in at least two frames of the video image; deriving a formula descriptive of a curve containing the tracking points; and upon determining the vehicle image is a measuring vehicle, deriving a scaling map comprising a scaling factor associating a vehicle image dimension, in the direction of travel, to a real-world vehicle dimension at a point collocated with the vehicle image in one frame of the video image.