Microscopic traffic flow characteristics are based on individual vehicle trajectories. Many characteristics are discussed. They are subdivided according to the amount of detail and are based on the vehicle trajectory itself, the time history of speed and the time history of acceleration respectively. Examples of characteristics at the three levels are trip time, standard deviation of the time history of speed and the spectral density of the time history of acceleration. Two kinds of relations between microscopic traffic flow characteristics are dealt with: those that can be derived directly from the definitions and those apparently following from the nature of the traffic process. Little research has, in fact, been carried out into the latter type of relation. Microscopic traffic flow characteristics are usually drawn up with the object of representing traffic flow quality aspects. This applies to traffic operation, because characteristics such as trip time, stopping time and delay are operationalisations of traffic operation aspects. As to hazards, no clear relationship with the characteristics has yet been demonstrated, but appears to be rather reasonable. Relationships with comfort are difficult to establish, because there is no suitable operational definition of this. Instrumented vehicles with test subjects and measuring systems observing random vehicles are suitable for collecting the characteristics. Both methods are briefly discussed and compared on a number of aspects. For part I-VI see IRRD abstracts nos 240606-240609 and 261941-2.
Abstract