Gap acceptance capacity model for on-ramp junction of urban freeway

The commonly-used capacity calculation approaches for ramp junctions are mostly based on the American HCM method, It had been approved that the headways for vehicles following the Weibull distribution function at on-ramp junctions in urban freeway system. The paper examined the critical headway and following time by the modified drew method and the survey traffic flow data on-site. The gap-acceptance capacity calculating model was developed for on-ramp junctions of urban freeway, and the numerical integration method was used to solving the model. Finally, the capacity values were obtained in condition of different mainline design speeds and different acceleration lane lengths. The result indicated that the capacity value would grow with increase of the acceleration length and mainline design speed, and the capacity values for on-ramp junctions would approach basic freeway segments capacity values while the acceleration lengths beyond 400 meters.