The evaluation of motorway reliability is a subject of great interest for researchers of traffic engineering. For easyrecognizable reasons, this subject is very important in theoretical studies and for applications, e.g. evaluation of capacity and trafficcontrol on motorway. In this paper the different conceptions of reliability in technical and scientific literature are compared with thefollowing definition: reliability of traffic stream, for a time interval T, is “the conditioned probability that level of speed spot processdoes not decrease during T as far as the section in which limit density is reached, given that the level at instant zero is equal to theaverage speed corresponding to the flow rate in condition of stable flow”. Then, a criterion to calculate the motorway reliability ispresented. The speed spot time-series are divided into sequences of events of random and homogeneous traffic processes. For everyprocess one can calculate two parameters: flow rate and density; then, one can obtain the relationships between the parameters ofspot speed processes and vehicular density. Using these relationships and a simulation procedure of spot speed process, one canobtain a formulation of the reliability of a traffic flow running along the offside lane of a motorway carriageway. Thus, through thisformulation and the measurements of flow rate and speeds, one can evaluate the probability of instability on the carriageway underinvestigation. On the other hand, with an inverse procedure one can calculate the capacity of one lane in this way: putting close to 1the reliability value and considering a 15 minutes time interval, the obtained flow rate represents capacity. In the paper, the procedureexplained is used to provide, in real time, the approaching of the instability on the carriageway and to calculate the carriagewaycapacity for the A22 Brenner Motorway (Italy).
|Number of pages||9|
|Publication status||Published - 2012|