Phase diagram distortion from traffic parameter averaging
Résumé
Motorway traffic congestion is a major bottleneck for economic growth. Therefore research on traffic behaviour is being carried out in many countries. Observations and theories of congested traffic, although well describing the free flow phase as an almost straight line in a density-flow or (k,q)-phase diagram, disagree in the congested flow state. In this paper we investigate the relation between traffic observations and the structure of the phase diagram. It focuses on the way speed observations are averaged, and how this influences the location of the averaged observations in the phase diagram. The analysis implies a phase diagram where the congested phase consists of a straight line. This straight right branch corresponds to upstream moving speed wave regions, called speed waves. The right branch connects the top of the free flow phase line with a point of maximum k and zero q. Its slope corresponds to the speed of the upstream moving speed wave, with a value of –18±1km/h, a value also found by other authors. By simulating traffic on this line, consisting of waves with two different speeds, we show that the location of averaged parameters in the phase diagram lie below this line. We also show that harmonic mean speed is a good indicator for travel time.
Domaines
Infrastructures de transport
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