To estimate the future volume of trips interchanging between each pair of zones within an urban area, a simple behavioral model of travel interaction is presented. The interactance model is subjected to a set of five constraints, which reflect pertinent conditions that should be fulfilled in the resulting distribution. A method is developed to distribute future trips in accordance with the interactance model so that all constraints will be satisfied. The constrained interactance model differs from other trip distribution models in that the distribution of trip lengths is constrained to result as given in advance. Furthermore, no model calibration is necessary. Rather than the conventional use of subjective judgements to distinguish the travel movements which warrant exogenous compensations to correct for socioeconomic biases, an objective procedure utilizing a statistical test is provided. Socioeconomic and geographic compensations, where needed, are applied between pairs of groups of contiguous and homogeneous zones rather than between individual zone pairs. A model is developed to determine the total number of zone pairs expected to have travel interactions in an urban area, as a function of the number of trips and zones. Another model which describes travel interaction propensities as related to travel disutility, is developed to indicate which pairs of zones are the least likely to have travel interactions, and should be dropped from the trip distribution, in order to restrict the number of travel interactions to the estimated total. ...