Link Travel Time Estimation in Double-Queue-Based Traffic Models

Double queue concept has gained its popularity in dynamic user equilibrium (DUE) modeling because it can properly model real traffic dynamics. While directly solving such double-queue-based DUE problems is extremely challenging, an approximation scheme called first-order approximation was proposed to simplify the link travel time estimation of DUE problems in a recent study without evaluating its properties and performance. This paper focuses on directly investigating the First-In-First-Out property and the performance of the first-order approximation in link travel time estimation by designing and modeling dynamic network loading (DNL) on single-line stretch networks. After model formulation, we analyze the First-In-First-Out (FIFO) property of the first-order approximation. Then a series of numerical experiments is conducted to demonstrate the FIFO property of the first-order approximation, and to compare its performance with those using the second-order approximation, a point queue model, and the cumulative inflow and exit flow curves. The numerical results show that the first-order approximation does not guarantee FIFO and also suggest that the second-order approximation is recommended especially when the link exit flow is increasing. The study provides guidance for further study on proposing new methods to better estimate link travel times.

Framework for Delay Guarantee in Multi-Domain Networks Based on Interleaved Regulators

The key to the asynchronous traffic shaping (ATS) technology being standardized in IEEE 802.1 time sensitive network (TSN) task group (TG) is the theorem that a minimal interleaved regulator (IR), attached to a FIFO system does not increase delay upper bound while suppresses the burst accumulation. In this work it is observed that the FIFO system can be a network for flows that share same input/output ports and same queues of the network, and are treated with a scheduling scheme that guarantees the FIFO property within a queue. Based on this observation, a framework for delay bound guarantee is further proposed, in which the networks with flow aggregates (FAs) scheduling and minimal IRs per FA attached at the network edge are interconnected. The framework guarantees the end-to-end delay bound with reduced complexity, compared to the traditional flow-based approach. Numerical analysis shows that the framework yields smaller bound than both the flow-based frameworks such as the integrated services (IntServ) and the class-based ATS, at least in the networks with identical flows and symmetrical topology.