Satish Ukkusuri's Publications

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Most Recent Papers

		Mobility of Vehicles improves* information flow in vehicular ad hoc networks* Written with L. Du In Review, Feb. 2007.
		Robust Signal Control Problem Accounting for Traffic dynamics Written with G. Ramadurai and G. Patil In Review, Dec. 2006.
		Dynamic Traffic Equilibrium under Information: An Experimental Network Game Approach Written with G. Ramadurai To appear in the Journal of Transportation Research Record, 2007.
		Exploring user behavior in online network equilibrium problems Written with G. Patil To appear in the Journal of Transportation Research Record, 2007.

Transportation Network Modeling

Dynamic Traffic Networks

S. Ukkusuri. Linear Programs for the Dynamic User Optimal Traffic Assignment Problem

Quick summary: Includes all material from the two papers below, plus additional introductory material, surveys of prior work, some additional extensions and open questions of interest in dynamic traffic networks.
Bibliographic info: M.S. Thesis, University of Illinois at Urbana Champaign. December 2002.

S.T.Waller, S. Ukkusuri. A Linear Programming Formulation for the User Optimal Dynamic Traffic Assignment Problem.

Quick summary: A Linear Programming (LP) approach for the User Optimal Dynamic Traffic Assignment (UODTA) problem is presented here. Proofs are given for the correctness of the formulation and solution. Numerical demonstrations are performed to analyze and compare the results to a known system optimal model.
Bibliographic info: Presented at the San Jose INFORMS 2002.
In Review Transportation Science

S. Ukkusuri,S.T.Waller. Linear Programming Models for the User and System Optimal Dynamic Network Design Problem: Formulations, Implementations and Comparisons.

Quick summary: The Network design problem is known to identify the critical links for improvement to reduce the inefficiency of user optimal routing. We propose a method based on the Cell Transmission Model to identify optimal budget improvements for single destination networks. We propose an approximation technique to solve reasonable sized traffic networks and compare the solutions with the known Combinatorial User Optimal Algorithm. We show the usefulness of this method and suggest directions for future research.
Bibliographic info: Conference version appeared in TRB 83rd Annual Meeting Proceedings (CD-ROM), In Review Networks and Spatial Economics. February 2007.

S. Ukkusuri, Ampol Karoonsoontawong,S.T.Waller. A Stochastic Dynamic User Optimal Network Design Model accounting for Demand Uncertainty.

Quick summary: Transportation network design problems have widely been researched under the assumption of deterministic demands for both static and dynamic networks. However, in reality, the demands are uncertain, and the traffic flow is dynamic in nature. This paper documents two formulations for the stochastic dynamic network design problem under user optimal conditions for single destination traffic networks: chance constraint model and two-stage recourse model. Initial results for the chance constraint model are presented along with some insights into the effect of demand uncertainty.
Bibliographic info: Conference version appeared in TRANSPO2004

Jane Je in Lee, Masao Kuwahara, S. Ukkusuri. Predictive Dynamic Assignment with Physical Queues based on Kinematic Wave Theory.

Quick summary: This research investigates the predictive dynamic user equilibrium (DUE) for the dynamic traffic assignment in a saturated network with physical queue concept. We derive the flow conservation conditions for the DUE based on kinematic wave theory and discuss the optimal conditions for the problem without proofs. We present a solution methodology for the problem based on link and path performance models and show important differences between the physical queue and point queue analysis through initial analysis on an example network.
Bibliographic info: Conference version appeared in TRB 83rd Annual Meeting Proceedings (CD-ROM),

K. Jeon, S. Ukkusuri and S.T.Waller, Selectorecombinative Genetic Algorithm to Relax computational Complexity of Discrete Network Design Problem.

Quick summary: This work develops an efficient evolutionary algorithm for solving the transportation network design problem.
Bibliographic info: Journal version Transportation Research Record: Journal of the Transportation Research Board, No. 1964, Transportation Research Board of the National Academies, Washington, D.C., pp. 91-103, 2006

Stochastic, Robust and Flexible Traffic Networks

S. Ukkusuri. Accounting for Uncertainty, Robustness and Online Recourse in Transportation Networks

Quick summary: Includes new formulations related to stochastic assessment of network congestion, robust network design and online recourse in traffic networks.
Bibliographic info: Ph.D. Dissertation, University of Texas at Austin. August 2005.

S. Ukkusuri and S.T.Waller, Approximate Analytical expressions for the traffic equilibrium problem under uncertain demand.

Quick summary: This research solves the traffic assignment problem when the long term demand is an uncertain quantity. A closed form expression for the system's expected value and variance are obtained. We believe that designing networks to minimize this variance would result in robust solutions. Further, the equilibrium properties under such kind of long term demand uncertainty are studied and verified using well known transportation test networks. The mean of the analytical expression performs well where as the robustness expression is a crude approximation.
Bibliographic info: Conference version appeared in TRISTAN V, Le Gosier, 2004, Journal version In Review, 2006

S. Ukkusuri, V.M. Tom and S.T.Waller, Robust Transportation Network Design under demand uncertainty.

Quick summary: In this research, instead of finding optimal network design solutions for a given future scenario, we are concerned with solutions which are in some sense 'good' for a variety of demand realizations. We propose a general definition of robustness and develop a methodology based on genetic algorithm (GA) to find robust network design (RNDP) solutions. The study makes two important contributions to the network design literature. First, robust network design solutions are significantly different from the deterministic NDPs and not accounting for them could underestimate the network wide impacts. Second, we systematically evaluate the computational performance by using different test networks and GA control parameter settings to obtain the appropriate parameters for this problem. The results highlight the importance of accounting for robust solutions in transportation planning.
Bibliographic info: In Computer Aided Civil and Infrastructure Engineering, 22, pp. 9-21 (2007).

S. Ukkusuri and S.T.Waller, Single Point Approximations for the traffic equilibrium problem under uncertain demand.

Quick summary: In this research, we develop single estimates for the traffic equilibrium problem under stochastic demand. We show which estimator performs consistently well on a test network and conclude with caveats on when single point approximations can be efficiently used.
Bibliographic info: In Transportation Research Record: Journal of the Transportation Research Board, No. 1964, Transportation Research Board of the National Academies, Washington, D.C., 2006, pp. 169-175

G. Patil and S. Ukkusuri, Stochastic system optimal network design problem.

Quick summary: In this research, we develop a two stage stochastic programming formulation of the system optimal network design problem with computational results. Especially we discuss the dependence of the results on the different penalty functions used in the recourse function of the problem.
Bibliographic info: In Print Transportation Research Record: Journal of the Transportation Research Board, 2007

Y. Kim, S. Ukkusuri, B.F. Spencer and S.T.Waller, Assessing transportation network performance under seismic conditions with stochastic capacity degradations .

Quick summary: Recently, there has been significant interest in protecting transportation networks in earthquakes due to the major role they play in propagating disturbances to related systems. All of the recent earthquakes (e.g. Northridge Earthquake December 14, 1994) involved heavy transportation infrastructure losses due to bridge damages, crippling the mobility of system users. In this research we are concerned with assessing network wide impacts under different earthquake scenarios which results in stochastic capacity reductions. We propose different sampling techniques for evaluating the network impacts and the best methodology is identified for this problem. This information can be beneficial not only in areas such as service, planning and repair scheduling of infrastructure/bridges but also in determining where an investment in improving the overall network performance is warranted.
Bibliographic info: Conference version appeared in Proceedings of the National Earthquake Engineering Conference (NEEC) in Los Angeles, 2006 . Journal Version: In Preparation.
Some press on our research:

Vehicular Ad Hoc Networks (V2V)

S.Ukkusuri, G. Ramadurai and L. Du Modeling limited peer to peer vehicle information exchange for online traffic assignment..

Quick summary: In this research we develop a simple algorithm for information exchange for vehicular ad hoc networks.
Bibliographic info: In Proceedings of the World Conference in Transportation Research, Berkeley, July 2007

S.Ukkusuri and L. Du Analytical expressions to characterize the connectivity of vehicular ad hoc networks..

Quick summary: In this research we develop a one dimensional network model for vehicular ad hoc networks. We obtain analytical expressions for the connectivity of vehicular ad hoc networks.
Bibliographic info: In Review

S.Ukkusuri and L. Du Mobility improves the information exchange in vehicular ad hoc networks..

Quick summary: In this research we account for lane changing behavior in traffic networks and show the value of mobility in information exchange in V2V networks. We derive analytical expressions and validate these expressions with a open-source dynamic traffic simulation model.
Bibliographic info: In Review

S.T.Waller, A. Unnikrishnan and S. Ukkusuri User Equilibrium with recourse.

Quick summary: In this work we tackle a fundamentally new problem of studying the effect of online information provision on transportation network users. We develop a formulation and a solution approach based on the concept of hyperpaths (policies). We show that the subproblem to the formulation is an online shortest path problem and perform computational analysis on different test networks.

Bibliographic info:

In Preparation

Humanitarian Supply Chains

In Print Transportation Research Record: Journal of the Transportation Research Board, 2007

In Proceedings of the Katrina Conference in New Orleans, November 2007

J. Holguin-Veras, N. Perez, S. Ukkusuri, T. Wachtendorf and B. Brown Emergency Logistics issues in Hurricane Katrina: A synthesis and preliminary suggestions for improvement.

Quick summary: In this research, we characterize the logistics issues after the Hurricane Katrina using extensive interviews and data.
Bibliographic info:

J. Holguin-Veras, N. Perez, S. Ukkusuri, T. Wachtendorf and B. Brown Logistics issues in the aftermath of extreme events: The Katrina experience.

Quick summary: In this research, we discuss the logistics issues after a major disaster.
Bibliographic info:

Transportation Systems Safety and Security

D.Sun, S. Ukkusuri R.F.Benekohal, S.T.Waller, Modeling of Pedestrian Gap Acceptance for Improving Safety at Uncontrolled Mid-block Crosswalks .

Quick summary: The purpose of this paper is to develop realistic models for pedestrian gap acceptance behavior at uncontrolled two-lane mid-block crosswalks. Different methodologies for modeling Pedestrian Gap Acceptance (PGA) are proposed. A field study was conducted to collect the data of different attributes using a set of video cameras at a typical unsignalized mid-block crosswalk. The results show that PGA binary logit models perform better than the other models.
Bibliographic info: Conference version appears in TRB 82nd Annual Meeting CD-ROM.
In Review

D.Sun, S. Ukkusuri, R.F.Benekohal, S.T.Waller, Fuzzy Logic based Online Collision Prediction System for Signalized Intersections.

Quick summary: A conceptual framework of online intersection collision prediction and avoidance system for signalized intersections is proposed. The risk is quantified by three fuzzy inputs to the model, the time to collision, severity of the crash and the local perception of the drivers. Perception Index and Severity Index are integrated to reflect driver-vehicle system safety characteristics. An example at a hypothetical intersection is presented to demonstrate the proposed methodology for the red light running vehicle.
Bibliographic info:
Advances in Transportation Studies An International Journal. Vol III (July 2004) pp. 71-86.

S. Ukkusuri and J. Holguin-Veras Assessing critical components in transportation systems: Economic Models and Complex Network Science Models.

Quick summary: This research abstracts the port as a network with a certain degree of connectivity and proposes a conceptual framework for identifying the critical components in the port network. The methodology proposed here is based on the science of complex networks which has been recently applied to protect communication networks against terrorism (Latora and Marchiori, 2004). A hypothetical port network (similar to the components of Houston Port network) is solved to show the applicability of this method. The methodology can be extended easily for large networks and the complexity of the problem is shown to be O (n6).
Bibliographic info: Book Chapter: In Network Science, Nonlinear Science and Infrastructure Systems. Editor: Terry L. Friesz, 2006

Operations Research Applications in Railroads

C.P.Barkan, S.Ukkusuri, S.T.Waller, Optimizing the design of railway tank cars to minimize accident caused releases

Quick summary: The design of vehicles transporting hazardous materials has important public safety and economic implications. Conventional wisdom among industry and government has held that a thicker tank on railroad tank cars and tank trucks reduces risk. In this research we develop a model that analyzes the tradeoff between increased damage resistance and greater exposure to accidents in which the objective function is minimization of the probability of release. The model accounts for the reduction in tank car release probability as a function of tank thickness, and the increased exposure to accidents that occurs due the increased number of shipments needed for the heavier car. Sensitivity analyses using the model indicate that for any particular configuration of tank car there is an optimal thickness. This optimal thickness is affected by several factors and there is no single optimum for all tank cars.
Bibliographic info: In Print Computers and Operations Research
This manuscript has gained timely relevance because of the recent accident in Graniteville, SC. Click here for more details.

I do remember one thing.
It took hours and hours,
But by the time I was done with it,
I was so involved,
I didn't know what to think.
I carried it around with me for days and days,
Playing little games,
Like not looking at it for a whole day,
And then looking at it,
To see if I still liked it.
I did!
- King Crimson, "Indiscipline", Discipline