Abstract: An automatic vehicle location center includes a control center and a plurality of mobile units. Each mobile unit is able to derive a current position from external radio signals. A prediction is responsive to this current position signal and to predicted motion of the mobile unit to derive a predicted position signal. The predicted and current positions signals are compared and the current position signal is transmitted to the control center in dependence on the result of the comparison. The control center has a predictor, similar to that in each mobile unit, responsive to the current position signal and to predicted motion of the mobile unit to derive a predicted position. This position data is only transmitted from a mobile unit to the control center if the predicted position signal differs significantly from the actual position.