Wei-Hua Lin

SHORT-TERM ARTERIAL TRAVEL TIME PREDICTION FOR ADVANCED TRAVELER INFORMATION SYSTEMS

While vehicular flows on freeways are often treated as uninterrupted flows, flows on arterials are conceivably much more complicated because vehicles traveling on arterials are not only subject to queuing delay but also to signal delay. Prediction of travel time is potentially more challenging for arterials than for freeways. This article proposes a simple model for arterial travel time prediction. The proposed approach decomposes total delay on an arterial into link delay and intersection delay. Intersection delay in the context of arterial travel time prediction is very different from the average delay at an intersection. The proposed approach reduces the delay at each intersection, a non-negative continuous variable, into two distinctive states, a state of zero-delay and a state of nominal delay, coupled with a one-step transition matrix that relates the delay to a through vehicle at an intersection to its delay status at the adjacent upstream intersection. The parameters of the transition matrix are based on three key factors: the flow condition, the proportion of net inflows into the arterial from the cross streets, and the signal coordination level. Comparison of predicted delay with simulated delay indicates that the model can yield predictions with a reasonable degree of accuracy under various traffic conditions and signal coordination levels.

A theoretical probe of a German experiment on stationary moving traffic jams

Abstract Kerner and Rehborn (Phys. Rev. E 53 (2) (1996)) reported on the observation of two stationary moving jams that lasted for about an hour on a 13 km long German highway section. They attributed the phenomenon to intrinsic characteristics of traffic flow, something that would arise spontaneously within the traffic stream due to drivers’ driving behavior. We show in this paper that these moving jams are not particularly peculiar but can be explained with the hydrodynamic theory of traffic flow, or the Lighthill–Whitham–Richards model, and the merge and diverge models in the cell transmission model. In fact, we demonstrate that this stationary jam phenomenon can be replicated with a simple two-wave velocity (or triangular) flow–density relationship in conjunction with the hydrodynamic theory. This finding provides some evidence to support that a triangular flow–density relationship is a good approximation of field observations and that a simple first-order hydrodynamic theory is capable of explaining complex traffic phenomenon.

ARE THE OBJECTIVE AND SOLUTIONS OF DYNAMIC USER-EQUILIBRIUM MODELS ALWAYS CONSISTENT?

Traffic assignment models are an important component in analyzing the relationship between demand and supply in the transportation network for design, planning, and control purposes. The static traffic assignment model has been used in practice for several decades. With the latest development in the area of Advanced Traffic Management Systems (ATMS) and Advanced Traveler Information Systems (ATIS), there is an increasing demand for dynamic traffic assignment models to serve as a basis for studying various issues in these areas. Existing dynamic user-equilibrium traffic assignment (DUETA) models are mostly expanded from the static user-equilibrium traffic assignment model by introducing the time dimension along with a group of additional constraints. Whereas the equivalency between the solution to the traffic assignment model and the user-equilibrium conditions as defined by Wardrop is well established in the static case, the same may not be true for the dynamic case. This paper examines the general form of DUETA models as proposed in previous research.

A Quasi-Dynamic Robust Control Scheme for Signalized Intersections

Conventional vehicle-actuated traffic signal control attempts to achieve system optimum by ending a phase as soon as queues served during that phase vanish. In this article, the authors extend this logic to intersections where a stable cycle length is desirable (e.g., for signal coordination or other considerations). The proposed control scheme dynamically updates green allocation to keep queues on all approaches well balanced. Different from fully dynamic control strategies, the proposed quasi-dynamic scheme is based on a finite set of fixed timing plans with a common cycle length. The decision of switching from one plan to another is made at the beginning of each cycle based on the queue state in the previous cycle. Our experimental results showed that the performance of the proposed scheme is robust with respect to random fluctuation, systematic changes in demand, and input data quality. Although the proposed scheme does not attempt to minimize total system delay directly, it provides a good solution for reducing total system delay compared with the signal timing plan optimized for system delay. The preservation of a stable cycle length in the proposed signal timing plan has made it possible to incorporate the proposed scheme into the development of control strategies for an arterial where signal coordination is essential to the performance of the system.

Response to “Comment on ‘Short-Term Arterial Travel Time Prediction for Advanced Traveler Information Systems’ by Wei-Hua Lin, Amit Kulkarni, and Pitu Mirchandani”

The discussion given in this note is in response to the comments by the discussant, T. Tsekeris.