V. Tools for urban transportation management
5.1 Traffic flows and models Traffic flow type is a complementary parameter to speed, which accommodates acceleration, deceleration, engine load, and pulsated or continuous traffic mo- tion. Four categories of traffic flows are defined below (EEA, 2002), (Commis- sion Recommendations, 2003): Fluid continuous flow. Vehicles move with nearly constant velocity on the road section of interest. It is “fluid” in that the flow is stable in both space and time for periods of at least ten minutes. Variations during the course of a day may be ob- served but without abrupt or rhythmic variations. Furthermore, it is neither accele- rated nor decelerated but remains at a steady velocity. This flow type corresponds to the traffic on a motorway/autobahn link or an inter-urban road, on an urban ex- pressway (outside rush hours), and on major roads in an urban environment. Pulsed continuous flow. A flow with a significant proportion of vehicles in a transitory state (i.e. either accelerating or decelerating), which is stable neither in time (i.e. there exist abrupt variations of flow during small time periods), nor in space (i.e. at any given moment in time, irregular concentrations of vehicles exist on the road section of interest). It remains possible, however, to define an aver- age overall velocity for this type of flow which is stable and repetitive for a suf- ficiently long period of time. This flow type corresponds to that found on city- centre roads, on major roads close to saturation, on dispatching or connecting roads with numerous...
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