A methodology for estimating capacity at ramp weaves based on gap acceptance and linear optimization

Freeway weaving areas are those formed when the paths of two or more traffic streams cross, i.e., when a merge area is closely followed by a diverge area, and the two are joined by an auxiliary lane. Previous research on weaving areas has mostly focused on developing methods for estimating speeds for the weaving and non-weaving traffic streams, and on determining freeway weaving level of service; there are no methods available for estimating freeway weaving capacity. The recently published Highway Capacity Manual (HCM, 2000) presents capacity values for weaving areas that are solely based on a density of 27 pc/km/ln. The objective of this study is to develop a method for estimating capacity of ramp weaves based on gap acceptance and linear optimization. The methodology provides estimates of the capacity of ramp weaves, as a function of the capacity of the equivalent basic freeway segment lane, and for given proportions of origin-destination demands within the weave. The paper presents the methodology along with results of the capacity estimation for the range of possible weaving and non-weaving flows. It also presents the results of sensitivity analyses conducted to assess the impact of the assumptions used in the methodology. Finally, the results obtained by this method are compared to the HCM (2000) capacity values.