Consider a problem in which the cost of building an irrigation canal has to be divided among a set of people. Each person has different needs. When the needs of two or more people overlap, there is congestion. In problems without congestion, a unique canal serves all the people and it is enough to finance the cost of the largest need to accommodate all the other needs. In contrast, when congestion is considered, more than one canal might need to be built and each canal has to be financed. In problems without congestion, axioms related with fairness (equal treatment of equals) and group participation constraints (no-subsidy or core constraints) are compatible. With congestion, we show that these two axioms are incompatible. We define weaker axioms of fairness (equal treatment of equals per canal) and group participation constraints (no-subsidy across canals). These axioms in conjunction with a solidarity axiom (congestion monotonicity) and another axiom (independence of at-least-as-large-length) characterize the sequential weighted contribution family. Moreover, when we include a stronger version of congestion monotonicity and other axioms, we characterize subfamilies of these rules.
