In force based models of pedestrian traffic, the relaxation time, τ, is related to the time it takes a pedestrian to adapt its motion to its preferences. An example of this is linear acceleration, but τ is also connected to how the agent adjusts to spatial variations in its preferred velocity, and affects evasive maneuvers. These many roles of τ may be a problem when calibrating force based models.

We compare linear acceleration, to new data on, and simulations of, turning movements. The results indicate that the models predict drifting of a magnitude that is not supported by the data.