Abstract:This paper studies steady-state traffic flow on a ring road with up-and down-slopes using a semi-discrete model. By exploiting the relations between the semi-discrete and the continuum models, a steady-state solution is uniquely determined for a given total number of vehicles on the ring road. The solution is exact and always stable with respect to the first-order continuum model, whereas it is a good approximation with respect to the semi-discrete model provided that the involved equilibrium constant states a… Show more
“…It is noted that in simulations, the initial state is the state in the last simulation instant rather than the traffic condition at the beginning of the simulation. That is, as shown in Zhang, Wu, and Wong (2012) and Wu et al (2014), similar to the many existing car-following models, the car-following model in this paper takes the current traffic states into account. SDE (3) indicates that the stochastic process S(t) follows a Geometric Brownian motion, and therefore, under Itō's interpretation of SDEs (Øksendal 2010), obeys a log-normal distribution with expected value E[S(t)] = S 0 e −βt and variance Var[S(t)] = S 2 0 e −2βt (e σ 2 t − 1).…”
A geometric Brownian motion car-following model: towards a better understanding of capacity drop, Transportmetrica B: Transport Dynamics, 7:1, 915-927,
ABSTRACTTraffic flow downstream of the congestion is generally lower than the pre-queue capacity. This phenomenon is called the capacity drop. Recent empirical observations show a positive relationship between the speed in congestion and the queue discharge rate. Literature indicates that variations in driver behaviors can account for the capacity drop. However, to the best of authors' knowledge, there is no solid understanding of what and how this variation in driver behaviors lead to the capacity drop, especially without lane changing. Hence, this paper fills this gap. We incorporate the empirically observed desired acceleration stochasticity into a car-following model. The extended parsimonious car-following model shows different capacity drop magnitudes in different traffic situations, consistent with empirical observations. All results indicate that the stochasticity of desired accelerations is a significant reason for the capacity drop. The new insights can be used to develop and test new measures in traffic control.
ARTICLE HISTORY
“…It is noted that in simulations, the initial state is the state in the last simulation instant rather than the traffic condition at the beginning of the simulation. That is, as shown in Zhang, Wu, and Wong (2012) and Wu et al (2014), similar to the many existing car-following models, the car-following model in this paper takes the current traffic states into account. SDE (3) indicates that the stochastic process S(t) follows a Geometric Brownian motion, and therefore, under Itō's interpretation of SDEs (Øksendal 2010), obeys a log-normal distribution with expected value E[S(t)] = S 0 e −βt and variance Var[S(t)] = S 2 0 e −2βt (e σ 2 t − 1).…”
A geometric Brownian motion car-following model: towards a better understanding of capacity drop, Transportmetrica B: Transport Dynamics, 7:1, 915-927,
ABSTRACTTraffic flow downstream of the congestion is generally lower than the pre-queue capacity. This phenomenon is called the capacity drop. Recent empirical observations show a positive relationship between the speed in congestion and the queue discharge rate. Literature indicates that variations in driver behaviors can account for the capacity drop. However, to the best of authors' knowledge, there is no solid understanding of what and how this variation in driver behaviors lead to the capacity drop, especially without lane changing. Hence, this paper fills this gap. We incorporate the empirically observed desired acceleration stochasticity into a car-following model. The extended parsimonious car-following model shows different capacity drop magnitudes in different traffic situations, consistent with empirical observations. All results indicate that the stochasticity of desired accelerations is a significant reason for the capacity drop. The new insights can be used to develop and test new measures in traffic control.
ARTICLE HISTORY
“…Although the Eulerian method is most commonly used, the Lagrangian method has been successfully applied to numerically solve the kinematic wave model as well. This has been done for homogeneous traffic (Leclercq 2007;Wu et al 2014), as well as mixed traffic including trucks (van Wageningen-Kessels et al 2011) and motor cyclists (Gashaw, Harri, and Goatin 2018). Examples of the Lagrangian method applied to second-order flow models are Greenberg (2001Greenberg ( , 2004; Zhang, Wu, and Wong (2012).…”
Section: Background On Macroscopic Modellingmentioning
Bicycles are gaining popularity as a mode of transport resulting in a mixed bicycle-car traffic situation on urban roads. Cyclists, however, are hardly included in traffic flow models which complicates the design of safe and congestion-free traffic situations. This work introduces class-specific speed functions based on two variables, being space headway for both cars and cyclists. This enables the macroscopic modelling of mixed bicycle-car traffic. The multi-class macroscopic flow model is successfully tested for different traffic situations that occur on urban roads where cyclists and cars share the same infrastructure, e.g. cyclists overtaking a queue of cars and cars overtaking cyclists with reduced speed. The mixed bicycle-car flow model allows travel time estimation of both classes, which in turn can be used to evaluate the overall performance of a mixed traffic road.
“…By (11), the steady-state ρ * (ξ, η) implies space-independence of φ * (η), and can be achieved only for stationary D in (η) and S out (η). The steady-state flow can be obtained in analogy with [15] who analysed it for a single ring road with bottlenecks, i.e., ∀η ∈ D the following holds…”
This paper addresses the problem of a boundary control design for traffic evolving in a large urban network. The traffic state is described on a macroscopic scale and corresponds to the vehicle density, whose dynamics are governed by a two dimensional conservation law. We aim at designing a boundary control law such that the throughput of vehicles in a congested area is maximized. Thereby, the only knowledge we use is the network's topology, capacities of its roads and speed limits. In order to achieve this goal, we treat a 2D equation as a set of 1D equations by introducing curvilinear coordinates satisfying special properties. The theoretical results are verified on a numerical example, where an initially fully congested area is driven to a state with maximum possible throughput.
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