Chronis Stamatiadis

Arterial-based control of traffic flow in urban grid networks

Urban networks are typically composed of a grid of arterial streets. Optimal control of the traffic signals in the grid system is essential for the effective operation of the network. In this paper, we present mathematical programming models for the development of optimal arterial-based progression schemes. Such schemes are widely used for traffic signal control in arterial streets. Under such a scheme, a continuous green band is provided in each direction along the artery at the desired speed of travel to facilitate the movement of through traffic along the arterial. Traditional schemes consist of uniform-width progressions. New approaches generate variable bandwidth progressions in which each directional road section is allocated an individually weighted weighted that can be adapted to the prevailing traffic flows on that link. Mixed-integer linear programming is used for the optimization. Simulation results indicate that this method can produce considerable gains in performance when compared with traditional progression methods. By introducing efficient computational techniques, this method also lends itself to a natural extension for incorporation in a dynamic traffic management system.

MULTIBAND-96: A PROGRAM FOR VARIABLE-BANDWIDTH PROGRESSION OPTIMIZATION OF MULTIARTERIAL TRAFFIC NETWORKS

Progression schemes are widely used for traffic signal control in urban arterial streets. Commonly available programs such as the MAXBAND or PASSER programs use the traditional approach, which consists of a uniform bandwidth design for each arterial. The multiband criterion, on the other hand, has the ability to adapt the progressions to the specific characteristics of each link in the network and thus obtain improved performance. The development and application of the multiband signal optimization scheme in multiarterial grid networks are described. The MULTIBAND-96 model optimizes all the signal control variables, including phase lengths, offsets, cycle time, and phase sequences, and generates variable bandwidth progressions on each arterial in the network. It uses the MINOS mathematical programming package for the optimization and offers considerable advantages compared with existing models. Simulation results using TRAF-NETSIM are given.

Integration of Dynamic Traffic Assignment with Real-Time Traffic Adaptive Control System

Intelligent transportation systems (ITS) are being designed to provide real-time control and route guidance to motorists to optimize traffic network performance. Current research and development efforts consist of a dynamic traffic assignment capability that can predict future traffic conditions and a real-time traffic adaptive control system (RT-TRACS) for generation of signal control strategies. Although these models are intimately connected, so far they have developed independently of one another. A framework is presented here for integrating the two models into a combined system with a practical approach for realizing it. First the static case involving the interaction between travelers (demand) and transportation facilities (supply) under recurrent conditions is discussed. This model is applicable in the design and planning of transportation systems management actions. The framework is then extended to the quasi-dynamic and the dynamic cases, which involve incorporation of advanced ITS technologies in the form of advanced traffic management systems and advanced traveler information systems. An innovative application of this framework to advanced traffic-adaptive signal control is presented using the hierarchic structure of RT-TRACS.

PROGRESSION OPTIMIZATION FEATURING ARTERIAL- AND ROUTE-BASED PRIORITY SIGNAL NETWORKS

Arterial progression schemes based on the bandwidth criterion are widely used for traffic signal optimization. The schemes provide robust plans for traffic control as well as a variety of design options that can be tailored to specific network and traffic conditions. In recent years, arterial progression optimization was also extended to grid networks. The programs use advanced mathematical programming models which are computationally demanding when applied to large-scale networks. This article describes procedures that dramatically improve the computability of such models and bring them into the realm of real-time application. The procedures are based on, first, selecting and optimizing an arterial priority network or a route priority network. Results are then used in a subsequent stage to determine an optimal plan for the entire network. The procedure is applicable to both uniform- and variable-bandwidth optimization and can accelerate computation by two orders of magnitude, ceteris paribus. This facilitates optimization of large-scale urban networks, provides a capability to analyze many design options and is also amenable for real-time implementation.

The BOOM Project: Towards 160 Gb/s Packet Switching Using SOI Photonic Integrated Circuits and Hybrid Integrated Optical Flip-Flops

We present a 160 Gb/s optical packet switching architecture that performs label detection and packet wavelength con- version using photonic components integrated on silicon-on-insulator (SOI) waveguide boards. For label detection, we report the fabrication of a 4-channel tunable, second-order microring resonator demultiplexer using the SOI nanowire waveguide platform. For all-optical wavelength conversion we report the integration and packaging of a cascaded SOI delay interferometer (DI) structure using SOI rib waveguides. Both components were assembled with an optical flip-flop to enable 160 Gb/s optical packet switching. The power penalty after the wavelength conversion process was ~4.5 dB with error performance well above the FEC limit. This work is part of the European ICT-BOOM project which aims at building a Tb/s photonic router using hybrid and heterogeneous integration on SOI substrates. The preliminary results reported here is the initial step before the final project demonstrator.

Fabrication and experimental demonstration of the first 160 Gb/s hybrid silicon-on-insulator integrated all-optical wavelength converter

We present a hybrid integrated photonic circuit on a silicon-on-insulator substrate that performs ultra high-speed all-optical wavelength conversion. The chip incorporates a 1.25 mm non-linear SOA mounted on the SOI board using gold-tin bumps as small as 14 μm. Τhe device performs chirp filtering and signal polarity inversion with two multi-mode interference (MMI) - based cascaded delay interferometers (DIs) monolithically integrated on the same SOI substrate. Full free spectral range (FSR) tuning of the DIs is accomplished by two independently tuneable on-chip thermal heaters. We demonstrate 160Gb/s all-optical wavelength conversion with power penalties of less than 4.6dB.

Advanced traffic control strategies for intelligent vehicle highway systems

This paper discusses traffic signal control strategies that are suitable for advanced traffic management within IVHS (Intelligent Vehicle Highway Systems). The strategies consist of a multi-level design for the real-time, traffic-adaptive control of the urban signal network system. Each control level has different response characteristics, with the more advanced levels incorporating in a nested fashion the capabilities of the lower levels. A principal goal of the new multi-level design is to invoke a selected control strategy when it can provide the greatest benefit.

Evaluation of the Massachusetts Motorist Assistance Program: Assessment of Congestion and Air Quality Impacts

A motorist assistance program has been operating in Massachusetts since 1995 to assist stranded motorists on selected freeway routes during the morning and evening peak periods. The program covers 21 major routes throughout the state, with one van, fully equipped to handle the majority of incidents encountered assigned to each route. To evaluate the program’s effectiveness a comprehensive analysis of a set of performance measures was carried out. The analysis consisted of simulating the program’s impact on each route category for all time periods and incident types. Benefit to cost ratios were calculated for each route and for the program as a whole. The program’s benefits far exceed the costs: the average value of the benefit to cost ratio is 19:1, whereas the values for the different routes range from 3:1 to 58:1. Overall, the program provides significant benefits in terms of reduction of travel time, fuel consumption, and emission of pollutants. The analysis results were also used to design an improved operations scheme on the routes that are served.

Development of Strategic Plan for Deployment of Intelligent Transportation System Equipment: Utility Index Decision Framework

This paper develops a methodology for the strategic placement of intelligent transportation system (ITS) devices such as variable message signs (VMSs) and closed circuit video equipment (CCVE) across a highway network. These devices are widely used by highway departments to observe and to detect highway incidents and to communicate with drivers. The devices have demonstrated effectiveness in reducing delays and accidents, increasing throughput, and providing real-time information to the motoring public. Although motorists cannot measure directly the benefits associated with these devices over their lifetime, this study has adopted surrogate measures for the evaluation of the benefits that accrue to motorists. The methodology uses a utility index decision criterion composed of the following four components: crash frequency, diversion opportunity, level of congestion, and traffic exposure. Each of these measures addresses an aspect of the benefits associated with the installation of the ITS elements. By combining them in a utility index, an overall measure of the benefits contributed by these elements can be obtained. The utility index is calculated for each link of the highway network, and a priority list for instrumenting the links with the highest potential return is developed. The methodology described in this paper was used to develop a strategic plan for the placement of VMSs and CCVE along the highway network operated by the Massachusetts Department of Transportation Highway Operations Center.

Combining Traffic Assignment and Adaptive Control in a Dynamic Traffic Management System

In this paper, the authors develop approaches for integrating traffic control and traffic assignment. The proposed method consists of an integration of the different levels of the Real Time Traffic Control System (RT-TRACS) hierarchy for traffic signal control with the predictive ability of dynamic traffic assignment (DTA) models.