Comparison of queue estimation accuracy by shockwave-based and input-output-based models

Abstract

Accurate queue estimation of traffic congestion at recurrent freeway bottlenecks is an important part of developing effective traffic control strategies. Two traffic flow analytical techniques are always employed in studying queuing processes: shockwave analysis and input-output analysis. These two techniques have been taken as separate tools for estimating queue length (size) in a number of studies. Shockwave analysis is particularly well-suited to evaluating the space occupied by the queuing process in units of length, e.g. metre, kilometre etc. Input-output analysis is always employed for vertical queue size in terms of the number of queued vehicles; however, some studies argued that this method underestimated queue size. This paper highlights the reason in the literature for underestimation of queue length with input-out analysis. The objective of this study was to compare real-time queue estimation accuracy using two proposed models based on the two analytical techniques, after investigating the dynamic characteristic of traffic flow at the bottleneck in the freeway. The parameters were determined using discrete field data collected along an urban freeway corridor, Whitemud Drive (WMD), in Edmonton,Canada. This study illustrated that although the two proposed models estimate queue length in different ways, they are compatible and capable of yielding accurate estimates of real-time queue length upstream of the studied bottleneck.

Framework model for time‐variant propagation speed and congestion boundary by incident on expressways

“…The input-output method assumes that the traffic passes through a bottleneck as a standard queuing problem, and determining traffic queues is based on the difference between the total inflows and outflows of a traffic facility. For instance, Jiang [7], Hegyi et al [8], Carlson [9], and Cao et al [10] utilised the input-output model to estimate queued vehicles and delays on freeways. Inherent advantages of this analysis method, its simplicity and utility, make it quite useful for measuring the vertical queue size on freeways.…”

“…This model is essentially an improved model of the input-output method, as it considers density variations caused by vehicle interactions. Moreover, it was found that the shockwave-based model outperformed the input-output-based model in the congestion boundary estimation [10,14]. The shockwave method considers the traffic analogous to the fluid flow, employing the wave representation of the traffic stream to model changes in traffic speeds and densities.…”

Queue length estimation at metered freeway‐to‐freeway connectors

“…Generally speaking, input-output method is commonly used for sizing queue length in terms of the number of queued vehicles. In comparison, shockwave method is particularly well-suited to estimating the space occupied by the queuing vehicles in units of length [14]. Although these two methods define queue lengths in different ways, numerous studies have demonstrated the consistency of input-output method and shockwave method [14][15][16][17].…”

“…In comparison, shockwave method is particularly well-suited to estimating the space occupied by the queuing vehicles in units of length [14]. Although these two methods define queue lengths in different ways, numerous studies have demonstrated the consistency of input-output method and shockwave method [14][15][16][17]. In summary, it was found that the input-output method, which is also known as the cumulative arrival and departure method [18], provides a simple and accurate queue length estimation and has been widely used in modeling queue and delay measures at different traffic facilities [19][20][21].…”