Priority-based access systems and methods for shared communication media are provided. The priority and a corresponding weight of traffic to be transmitted on a shared communication medium are determined. This determination may be made, for example, before a first attempt to transmit the traffic, or before a subsequent traffic transmission attempt following an unsuccessful transmission attempt. The weight controls a rate of change of an exponential delay range limit factor in proportion to a number of attempts to transmit the traffic. The resultant weighted delay range limit factor is used to determine a range of delays from which a delay is selected. A transmission back-off time is then determined based on the selected delay.