Maximum Possible Weaving Volume for Effective Operations of Ramp-Weave Areas: Online Estimation

Abstract

Understanding the behavior of weaving flows and estimating the effects of time-variant traffic conditions on the capacity of weaving areas are of critical importance in developing effective operational strategies for freeway management. An online procedure for estimation of the maximum possible weaving volume over time for a given ramp-weave area is presented. The method is based on the findings from weaving behavior analysis, which indicates that under moderate to heavy flow conditions the diverging vehicles, that is, the freeway-to-ramp vehicles, tend to move to the auxiliary lane on entering the weaving area, whereas the ramp-to-freeway vehicles travel a short portion of the auxiliary lane before they merge to the main line. Therefore, the beginning portion of an auxiliary lane in a ramp-weave area is shared by both merging and diverging vehicles, and the length of such a shared area, called the effective weaving zone, varies depending on the length of a given weave section and the amount of weaving flow. Such join-then-split weaving behavior implies that the maximum value of the weaving volume in a ramp-weave area with one auxiliary lane is limited by the maximum through capacity of one lane. The proposed method reflects the weaving behavior described above and determines the maximum possible weaving volume for a given time interval as a function of exit and merge capacities, which are dependent on the traffic conditions downstream of weaving areas. Preliminary test results with 5 min of data from a ramp-weave site indicate that the maximum possible weaving volume is estimated with reasonable accuracy.