Traffic Paradoxes Research Articles

Location of transit-oriented development stations based on multimodal network equilibrium: Bi-level programming and paradoxes

The unique relationship between the value capture mechanism (VCM) and transit-oriented development (TOD) stations and their peripheral areas, which progressively develops an expanded multimodal network, is well acknowledged in the transport industry. However, in regards to the location of TOD stations, insufficient attention has been paid to user travel behaviours and the operating mechanism of the multimodal network. To bridge this research gap, we develop a bi-level programming model for the location of TOD stations that analyses user travel behaviour in the multimodal network. The VCM and transit priority are the objectives of the upper level of this multi-objective optimization model. And the lower level of the model is a modified multimodal network equilibrium based on the Davidson function. Using a simple numerical simulation, this study proposes explanations for some traffic paradoxes from the perspective of a multimodal network equilibrium. We also illustrate competition and collaboration between rail and bus transport systems. Finally, this study uses an empirical case to describe the feasibility and applicability of the model. The results demonstrate that the location of TOD stations is not only one of the keys to the competitiveness of public transport but is also relevant to implementing its VCM.

Paradox links can improve system efficiency: An illustration in traffic assignment problem

This paper demonstrates a counter-intuitive phenomenon that “paradox links” (i.e. marginally improving or adding these links will increase a system's cost) can sometimes decrease a system's cost. It can be expressed that simultaneously improving the paradox link to a certain threshold (rather than only marginal improvement) or adding more paradox links may counter-intuitively avoid the paradox. Here, we refer this phenomenon as the “non-monotonicity” of the paradox with regard to the degree of link improvement and the number of additional paradox links. Firstly, a formal definition of "non-monotonicity" property of paradox in a rigorous mathematical manner is proposed. Then this non-monotonicity property is demonstrated to widely exist in the user equilibrium (UE), the stochastic assignment, and the stochastic user equilibrium (SUE) models by two simple networks, where the underlying reasons for this phenomenon in different scenarios are analyzed and compared. Finally, the non-monotonicity of the traffic paradox is corroborated in a road sub-network of Harbin. The conclusions of this study provide new insights into features of traffic paradoxes and new ideas to eliminate them.

Traffic Paradox Under Different Equilibrium Conditions Considering Elastic Demand

Traffic paradox is an important phenomenon which needs attention in transportation network design and traffic management. Previous studies on traffic paradox always examined user equilibrium (UE) or stochastic user equilibrium (SUE) conditions with a fixed traffic demand (FD) and set the travel costs of links as constants under the SUE condition. However, traffic demand is elastic, especially when there are new links added to the network that may induce new traffic demand, and the travel costs of links actually depend on the traffic flows on them. This paper comprehensively investigates the traffic paradox under different equilibrium conditions including the user equilibrium and the stochastic user equilibrium with a fixed and elastic traffic demand. Origin-destination (OD) mean unit travel cost (MUTC) has been chosen as the main index to characterize whether the traffic paradox occurs. The impacts of travelers’ perception errors and travel cost sensitivity on the occurrence of the traffic paradox are also analyzed. The conclusions show that the occurrence of the traffic paradox depends on the traffic demand and equilibrium conditions; higher perception errors of travelers may lead to a better network performance, and a higher travel cost sensitivity will create a reversed traffic paradox. Finally, several appropriate traffic management measures are proposed to avoid the traffic paradox and improve the network performance.

Traffic assignment paradox incorporating congestion and stochastic perceived error simultaneously

ABSTRACTThis paper analyses the effects of congestion and stochastic perceived error in stochastic traffic assignment paradox, by the measure of both actual and perceived travel cost. Two different circumstances are studied: improving an existing link and adding a new link. It is found that different congestion cost functions and perceived error levels will significantly affect the road condition and the demand level under which paradox happens. Moreover, how the interaction between traffic demands of different O-D pairs affects the occurrence of traffic paradox is illustrated by a two O-D pairs’ network. Besides, a counter-intuitive phenomenon when less stochastic perceived error yet increases the average travel cost (information paradox) is also discussed. The results of this paper help to understand the interactional impact of congestion and stochastic perceived error, and give some new insights to traffic paradox.

Traffic paradox on a road segment based on a cellular automaton: Impact of lane-changing behavior

The traffic paradox “faster is slower” does not always apply. To study when and where it is valid, a simulation for a real road segment is performed using a novel cellular automaton. This simulation is used to analyze the change in global traffic flow status during free lane-changing behavior under general urban traffic conditions. The impact of lane-changing behavior is quantified into two aspects, time and space, and are described by average delay and transitable flow, respectively. Then surfaces are obtained, which adopt the arriving probability of vehicles and the green ratio as dual independent variables. Thus by the comparison of two surfaces, free lane-changing and straight proceeding, the horizontal projection of the intersecting lines is solved. Finally, the range of occurrence and reasons for the paradox are analyzed.

Understanding Transportation Systems Through the Lenses of Experimental Economics: A Review

Planning, operation and analysis of transportation systems hinge on theories and assumptions regarding individual choices, traffic flows, and traffic equilibria. Transportation field data collection, however, often lacks sufficient control, and therefore is often not suitable to test theories in transport modelling and their underlying behavioural axioms. With increased pressure on transport planners to deliver efficient, safe and publicly acceptable plans, it is imperative for transport scientists to find alternatives when testing the behavioural axioms that underpin current theories. Transportation scientists have, in response, increasingly used methods from experimental economics to gain insights into behaviour as well as to test theories and policies. Here we review and critically analyse the use of the experimental method in transportation science. Specifically, we synthesize the findings of experimental studies with regard to safety, freight, route choice, departure time choice, and location choice. We also reflect on well-known traffic paradoxes. We find that some of the evidence for traffic paradoxes can be attributed to experimental artefacts and that experimental studies when conducted by engineers tend to lack dominance and when conducted by economists tend to lack salience. Dominance and salience are key precepts of the external validity of studies drawing on methods from experimental economics. This review work also highlights methods that strengthen dominance and salience when using experimental economics in transportation studies.

OVERCOMING THE PIGOU–DOWNS PARADOX USING ADVANCED TRAFFIC SIGNAL CONTROL

Expansion of a road network has often been observed to cause more congestion and has led researchers to the formulation of traffic paradoxes such as the Pigou–Downs and the Braess paradoxes. In this paper, we present an application of advanced traffic signal control (ATSC) to overcome the Pigou–Downs paradox. Port Louis, the capital city of Mauritius is used to investigate the effect of using a harbor bridge to by-pass the city center. Using traffic cellular automata (TCA) simulations it has been shown how, if traffic is only gradually deviated along the by-pass, an overall longer travel time and decreased flux would result. By making use of ATSC, which involves traffic lights that sense the number of vehicles accumulated in the queue, better travel times and fluxes are achieved.

Traffic Paradoxes and Economic Solutions

ABSTRACT Previous studies on traffic congestion have emphasized supply-side instruments, such as the expansion of road capacity and improving the management of traffic. However, researchers on transportation have identified several paradoxes in which the usual remedy for congestion—expanding the road system—is ineffective or even counterproductive. This paper presents three paradoxes of traffic flow in their general form and provides economic solutions to overcome them, with an emphasis on demand-side policies by examining the behavior of commuters and using pricing mechanisms.

The Braess paradox in mechanical, traffic, and other networks

We examine a network of strings and springs that exhibit counter-intuitive behavior. When a support string is cut, the load rises instead of falling. Our experimental and theoretical results lead to some general qualitative conditions for the existence of this paradoxical behavior, including effects of nonideal and nonlinear components. A simple procedure is given for doing a classroom demonstration of this behavior. This behavior is analogous to the well-known Braess paradox in traffic networks and also has (not well known) analogs in electrical, hydraulic, and thermal networks. Some new insights into the traffic paradox are gained from a study of the mechanical paradox.