Chin-Woo Tan

Traffic Measurement and Vehicle Classification with Single Magnetic Sensor

Wireless magnetic sensor networks offer a very attractive, low-cost alternative to inductive loops for traffic measurement in freeways and at intersections. In addition to vehicle count, occupancy and speed, the sensors yield traffic information (such as vehicle classification) that cannot be obtained from loop data. Because such networks can be deployed in a very short time, they can also be used (and reused) for temporary traffic measurement. This paper reports the detection capabilities of magnetic sensors, based on two field experiments. The first experiment collected a two-hour trace of measurements on Hearst Avenue in Berkeley. The vehicle detection rate is better than 99 percent (100 percent for vehicles other than motorcycles); and estimates of vehicle length and speed appear to be better than 90 percent. Moreover, the measurements also give inter-vehicle spacing or headways, which reveal such interesting phenomena as platoon formation downstream of a traffic signal. Results of the second experiment are preliminary. Sensor data from 37 passing vehicles at the same site are processed and classified into 6 types. Sixty percent of the vehicles are classified correctly, when length is not used as a feature. The classification algorithm can be implemented in real time by the sensor node itself, in contrast to other methods based on high scan-rate inductive loop signals, which require extensive offline computation. We believe that when length is used as a feature, 80-90 percent of vehicles will be correctly classified.

Bifurcation, chaos, and voltage collapse in power systems

A model of a power system with load dynamics is studied by investigating qualitative changes in its behavior as the reactive power demand at a load bus is increased. In addition to the saddle node bilification often associated with voltage collapse, the power system exhibits sub- and supercritical Hopf bifurcations, cyclic fold bifurcation, and period doubling bifurcation. Cascades of period doubling bifurcation terminate in chaotic invariant sets. The presence of these new bifurcations motivates a reexamination of the saddle-node bifurcation as the boundary of the feasible set of power injections.

Signal processing of sensor node data for vehicle detection

We describe an algorithm and experimental work for vehicle detection using sensor node data. Both acoustic and magnetic signals are processed for vehicle detection. We propose a real-time vehicle detection algorithm called the adaptive threshold algorithm (ATA). The algorithm first computes the time-domain energy distribution curve and then slices the energy curve using a threshold updated adaptively by some decision states. Finally, the hard decision results from threshold slicing are passed to a finite-state machine, which makes the final vehicle detection decision. Real-time tests and offline simulations both demonstrate that the proposed algorithm is effective.

Interruptible electric power service contracts

Abstract A two-period model is considered. In period 1 the electric power company offers for sale a set of contracts (ϱ 1 ,p 1 ),(ϱ 2 ,p 2 ),....Each consumer must select one contract k and d units of energy for which she pays p k d. The company must deliver d units of energy in period 2 with probability ϱ k ; the service may be interrupted with the complementary probability 1 − ϱ k . The problem is to design the optimal set of contracts to maximize social welfare when demand and supply may be random and when customers suffer a welfare loss due to service interruption. The best design is shown to be a solution to an optimal control problem. The results contrast sharply with previous work on the problem of pricing electric power in the face of random supply or demand.

A Model for Pricing Interruptible Electric Power Service

The current allocation of electric energy is based on a system of fixed prices. In such a system the gap between marginal cost of energy generation and the marginal value of energy consumption, hence the resulting inefficiency, is quite large [10]. One scheme that closes this gap is that of spot pricing, [11], [3], [2].

Analysis of Communication Channel Establishment in a Transit Signal Priority System

A critical issue encountered in implementing a transit signal priority system is to ensure that communication between transit vehicles and the traffic centre can be established for transmitting priority request and arrival time information needed for executing signal priority control. The available communication channel bandwidth, however, is not guaranteed to meet the demand from a potentially large number of transit vehicles requesting signal priority service. In this paper, we define and analyse this supply-demand problem with simulations of a simple time model. The emphasis is to investigate the logistic issues and identify the critical parameters, so that this simple model might serve as a framework for constructing a more complex realistic model upon which an efficient scheduling protocol could be designed to meet signal priority service demand.

Theory of the potential energy boundary surface

In this paper we provide a theoretical foundation of the PEBS method. First, we study the properties of the stability boundary of a gradient system. We then relate the stability boundary of a class of second-order dynamical systems to the gradient system. Using these results, we analyze the PEBS method. Conditions under which the PEBS method gives accurate stability estimate are discussed.

Development of a Hierarchical BRT System Architecture

This paper discusses the development of a system architecture for intelligent transportation systems (ITS) applications for bus rapid transit (BRT) systems. In the course of the development of system architecture, it is critical to take a system engineering approach in the development of BRT architecture to assess BRT service needs (or features), the functional realization of these service needs and the means of technological implementation. Motivated by the national ITS architecture, the BRT architecture has a hierarchy of three layers: application, physical, and logical. The application layer consists of the BRT service needs or features. For the physical layer, we first discuss a functional analysis that begins with the identification of system operational features, followed by an identification of the functions that are needed to achieve these operational features. We create a physical architecture modeled around each of the BRT features. In the final step, the logical architecture is traced or mapped from the physical architecture in such a way that the physical layer implements the processes identified in the logical architecture and assign them to subsystems, and the data flows that originate from one subsystem and end at another are grouped together into architecture flows