Correct Answer - Option 2 : Trip distribution
Concept-
The gravity model is much like Newton's theory of gravity.
Gravity model is used in transportation planning process for trip distribution.
The gravity model assumes that the trips produced at an origin and attracted to a destination are directly proportional to the total trip productions at the origin and the total attractions at the destination.
The calibrating term or "friction factor" (F) represents the reluctance or impedance of persons to make trips of various duration or distances.
The general friction factor indicates that as travel times increase, travelers are increasingly less likely to make trips of such lengths. Calibration of the gravity model involves adjusting the friction factor.