A Bathtub Model of Downtown Traffic Congestion ( 8 page pdf, Richard Arnott, ACCESS, University of California, Jun. 10, 2015)
Today we review an analysis of the degree of congestion as a function of the timing of commuting and how applying a congestion charge can alter the flow sufficiently to allow free flowing traffic. This approach is called the bathtub model as it resembles the flow of water through a drain- as the water depth builds up the drainage rate increases up to a critical point when it decreases. In the same way, traffic reaches full congestion and then the flow slows down. Applying higher tolls as the traffic begins to reach the critical point reduces the traffic density and allows the flow to increase again.
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