ITS Berkeley

Characterization of the Bullwhip Effect in Linear, Time-Invariant Supply Chains: Some Formulae and Tests

Ouyang, Yanfeng
Daganzo, Carlos F.
2006

The authors analyze the bullwhip effect in multistage, decentralized supply chains operated with linear and time-invariant inventory management policies; the focus is on robustness. The supply chain is modeled as a single-input, single-output control system driven by arbitrary customer demands. The authors derive robust analytical conditions to predict the presence of the bullwhip effect and bound its magnitude, based only on the way inventories are managed. These results hold independently of the customer demand. The authors also characterize the stream of orders placed at any stage of...

Bus Lanes with Intermittent Priority: Strategy Formulae and an Evaluation

Eichler, Michael
Daganzo, Carlos F.
2006

This paper evaluates strategies for operating buses on signal-controlled arterials using special lanes that are made intermittently available to general traffic. The advantage of special bus lanes, intermittent or dedicated, is that they free buses from traffic interference; the disadvantage is that they disrupt traffic. We find that bus lanes with intermittent priority (BLIPs), unlike dedicated ones, do not significantly reduce street capacity. Intermittence, however, increases the average traffic density at which the demand is served, and as a result increases traffic delay. These delays...

Double-Cycling Strategies for Container Ships and Their Effect on Ship Loading and Unloading Operations

Goodchild, Anne V.
Daganzo, Carlos F.
2006

Loading ships as they are unloaded (double cycling) can improve the efficiency of a quay crane and container port. This paper describes the double-cycling problem, and presents solution algorithms and simple formulae to determine reductions in the number of operations and operating time using the technique. We focus on reducing the number of operations necessary to turn around a row of a ship. The problem is first formulated as a scheduling problem, which can be solved optimally. A simple lower bound for all strategies is then developed. We also present a greedy algorithm that yields a...

Bus Lanes with Intermittent Priority: Strategy Formulae and an Evaluation

Eichler, Michael
Daganzo, Carlos F.
2006

This paper evaluates strategies for operating buses on signal-controlled arterials using special lanes that are made intermittently available to general traffic. The advantage of special bus lanes, intermittent or dedicated, is that they free buses from traffic interference; the disadvantage is that they disrupt traffic. We find that bus lanes with intermittent priority (BLIPs), unlike dedicated ones, do not significantly reduce street capacity. Intermittence, however, increases the average traffic density at which the demand is served, and as a result increases traffic delay. These delays...

Empirical Reassessment of Traffic Operations: Freeway Bottlenecks and the Case for HOV Lanes

Cassidy, Michael J.
Daganzo, Carlos F.
Jang, Kitae
Chung, Koohong
2006

An earlier empirical study of San Francisco Bay Area freeways concluded that HOV lanes unfavorably affect freeway traffic by creating congestion. That study attributed the observed congestion to HOV lanes and tentatively recommended their elimination over the full lengths of the freeways it examined; and even from all Bay Area freeways. It recognized, however, that its analysis is fragmentary and recommended further work to solidify its conclusions. This is logical since the study lacks a spatiotemporal analysis to pinpoint where and how congestion first forms (at bottlenecks).The present...

Macroscopic Modeling of Traffic in Cities

Geroliminis, Nikolas
Daganzo, Carlos F.
2007

Most of the existing models for large scale arterial networks are not realistic and appropriate to deal with crowded conditions. As an alternative, we propose observation-based models that circumvent the fragility problems of traditional models. Monitoring replaces prediction, and the system is repeatedly modified based on observations. To succeed this goal a city is modeled in an aggregated manner and relations between state variables are developed. Macroscopic control strategies are introduced which rely on real-time observation of relevant spatially aggregated measures of traffic...

Impacts of Lane Changes at Merge Bottlenecks: A Theory and Strategies to Maximize Capacity

Laval, Jorge
Cassidy, Michael
Daganzo, Carlos
Schadschneider, Andreas
Pöschel, Thorsten
2007

Recent empirical observations at freeway merge bottlenecks have revealed (i) a drop in the bottleneck discharge rate when queues form upstream, (ii) an increase in lane-changing maneuvers simultaneous with this “capacity drop”, and (iii) a reversal of the drop when the ramp is metered.

Counteracting the Bullwhip Effect with Decentralized Negotiations

Ouyang, Yanfeng
Daganzo, Carlos F.
2007

This paper shows how to reduce the bullwhip effect by introducing advance demand information (ADI) into the ordering schemes of supply chains. It quantifies the potential costs and benefits of ADI, and demonstrates that they are not evenly distributed across the chain. Therefore, market-based strategies to re-distribute wealth without penalizing any supplier are presented. The paper shows that if a centralized operation can eliminate the bullwhip effect and reduce total cost, then some of this reduction can also be achieved with decentralized negotiation schemes. Their performance is...

The Bullwhip Effect in Supply Chains with Stochastic Dynamics

Ouyang, Yanfeng
Daganzo, Carlos F.
2007

This paper analyzes the bullwhip effect in single-echelon supply chains operated nondeterministically. The supply chain is modeled as a Markovian jump linear system driven by arbitrary customer demands. The paper presents robust analytical conditions to diagnose the bullwhip effect, and bound its magnitude. The tests are independent of the customer demand. Examples are given. Policies that pass these tests, and thus avoid the bullwhip effect in random environments for arbitrary customer demands, are shown to exist. The paper also presents extended tests for multi-echelon chains.

Continuum Approximation Techniques for the Design of Integrated Package Distribution Systems

Smilowitz, Karen R.
Daganzo, Carlos F.
2007

Complex package distribution systems are designed using idealizations of network geometries, operating costs, demand and customer distributions, and routing patterns. The goal is to find simple, yet realistic, guidelines to design and operate a network integrated both by transportation mode and service level; i.e., overnight (express) and longer (deferred) deadlines. The decision variables and parameters that define the problem are presented along with the models to approximate total operating cost. The design problem is then reduced to a series of optimization subproblems that can be...