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 The discussion of the speed-flow-density relationship mentioned several speed-density conditions. Two of these conditions are extremely significant and have been given special names. Free Flow Speed This is the mean speed that vehicles will travel on a roadway when the density of vehicles is low. Under low-density conditions, drivers no longer worry about other vehicles. They subsequently proceed at speeds that are controlled by the performance of their vehicles, the conditions of the roadway, and the posted speed limit. Jam Density Extremely high densities can bring traffic on a roadway to a complete stop. The density at which traffic stops is called the jam density.
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