United States Department of Transportation
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Edition:Dissertation 04/01/2020 – 07/02/2021
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Abstract:The effective management and operation of existing freeway facilities has become a preferred approach to reduce traffic congestion. Weaving areas are characterized by frequent lane changes, which significantly reduce the capacity of the freeway system. These are common design elements on freeway facilities between an on ramp and off ramp with an auxiliary lane. They are located between merge and diverge points, near ramps where a lane is added or dropped, and at multilane ramps. A weaving section is a freeway segment in which traffic flows cross each other without traffic control (Minderhoud et al. 2003). Traffic demands exceeding segment capacity at weaving areas cause congestion, which affects the operation of the entire freeway section. A significant amount of research has been done to estimate quality of service and capacity in weaving sections. However, little has been done to address multiple weaves. A multiple weaving area is one where two or more weaving areas overlap. No satisfactory means of estimating capacity has been found. This work examines capacity and quality of service conditions for a specific example of a multiple weave. Capacity is evaluated through micro-simulation by gradually raising flows for a range of geometric and fraction of weaving-traffic conditions. Models are developed to express capacity in terms of lane configuration, flow ratios, traffic mix (heavy traffic percentages), and overall flow rate. This study is limited to cases where there are two overlapping weaving movements created by two entry ramps following by an exit ramp. The study develops relations for capacity and service volume for a range of geometric, flow conditions, and traffic mix. Geometric conditions include number of lanes on the main lane entry and each entrance ramp into and exit ramp from the weaving area (n), and distances (Ls) between ramps. Flow conditions include a range of flows from each of the entry and exit roadways (V) in the multiple weaving area. The traffic mix represents the fraction of heavy vehicles in the traffic stream (PHV). In order to estimate the capacity of the weaving area, repeated simulations are performed under varying factors, number of lanes, flow range, heavy vehicle percentage, and routing. VISSIM outputs include link evaluation (average values for the link), and data collection (point measurement) files are extracted. These output files allow us to extract parameters, such as space-mean speed for links, to identify the point at which speed start to drop. Also, entry and exit volumes to see if they are the same as the summation of input volume that we specified in the run. The point that speed starts dropping significantly, or the summation of exit or entrance volume is much lower than what we entered in the system, suggests that we have reached the capacity point. To estimate capacity, we will consider all possible combinations of car following parameters to see what gives us the maximum capacity. At the same time, we will adjust different variables/factors we have introduced (number of lanes, flow, etc.) to see which one will give us a higher throughput, which is the capacity.
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