A recipe for jam - can congestion be defined consistently?

Congestion is widely predicted to increase, but the term is subjective. Where unavoidable delay becomes `congestion´ is hard to define. Marginal delay imposed by travellers on each other appears a more consistent measure than the popular Congestion Index (CI) or Level Of Service (LOS), but still offers no definite onset threshold, so the only objective criterion may be ratio of demand to capacity. However congestion is defined, its cost must be weighed against the cost of relief. However, without a culture change, adaptation is likely to maintain congestion at the level of toleration.