WNCG - Wireless Networking and Communications Group - Transportation Research
http://wncg.org/tags/transportation-research
enTraffic assignment with uncertain travel times
http://wncg.org/research/briefs/traffic-assignment-uncertain-travel-times
<div class="field field-name-field-publish-date field-type-datetime field-label-hidden"><div class="field-items"><div class="field-item even"><span class="date-display-single">Wednesday, March 19, 2014</span></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"> <p>As vehicles become smarter, increasingly automated and with access to massive amounts of data, they become better equipped to commucate, coordinate and compute optimal routes so as to minimize congestion. Such coordination is modeled by routing games, where a central goal is to understand and compute a socially optimal traffic assignment that minimizes overall congestion. </p>
<p>WNCG Prof. Nikolova and Prof. Stier-Moses from Universidad Di Tella, Argentina are laying the theoretical foundation of how risk aversion and uncertainty transform classic routing games. Routing games were one of the principal examples in the development of algorithmic game theory. In these games, multiple users need to route between different source-destination pairs and edges are congestible, namely, each edge delay is a non-decreasing function of the flow or number of users on the edge. A key motivation for studying routing games is understanding and mitigating congestion in transportation networks. However, unlike the classic routing game model where edge delays are known, in reality they are uncertain—heavy and uncertain traffic conditions exacerbate the commuting experience of millions of people across the globe. When planning important trips, commuters typically add an extra buffer to the expected trip duration to ensure on-time arrival.</p>
<p>Motivated by this, in a recent paper Nikolova and Stier-Moses propose and analyze a new traffic assignment model that takes into account uncertain travel times and risk-averse users. Users capture the tradeoff between travel times and their variability in a mean-standard deviation objective, defined as the mean travel time plus a risk-aversion factor times the standard deviation of travel time along a path. The paper provides a characterization of an equilibrium traffic assignment and provides conditions when it exists. The main challenge is posed by the users’ risk aversion, since the mean-standard deviation objective is nonconvex and nonseparable, meaning that a path cannot be split as a sum of edge costs. As a result, even an individual user’s subproblem—a stochastic shortest path problem—is a nonconvex optimization problem for which no polynomial time algorithms are known. In turn, the mathematical structure of the traffic assignment model with stochastic travel times is fundamentally different from the classic deterministic model. In particular, an equilibrium characterization requires exponentially many variables, one for each path in the network, since an edge-flow has multiple possible path-flow decompositions that are not equivalent. Because of this, characterizing the equilibrium and the socially-optimal traffic assignment, which minimizes the total user cost, is more challenging than in the traditional deterministic setting. Nevertheless, the paper proves that both can be encoded by a representation with just polynomially-many paths. Also, under the assumption that the standard deviations of travel times are independent from edge loads, it shows that the worst-case ratio between the total user cost in an equilibrium and that of an optimal solution is not higher than the analogous ratio in the deterministic setting. In other words, uncertainty does not further degrade the system performance in addition to strategic user behavior alone.</p>
<p>Read full journal paper: <a href="http://users.ece.utexas.edu/~nikolova/papers/stochWardropEqFinalOR.pdf" target="_blank">http://users.ece.utexas.edu/~nikolova/papers/stochWardropEqFinalOR.pdf </a></p>
<p>Earlier conference abstract: <a href="http://users.ece.utexas.edu/~nikolova/papers/SAGT2011-Paper39.pdf" target="_blank">http://users.ece.utexas.edu/~nikolova/papers/SAGT2011-Paper39.pdf </a></p>
<p>Technical summary: <a href="http://www.sigecom.org/exchanges/volume_11/1/NIKOLOVA.pdf" target="_blank">http://www.sigecom.org/exchanges/volume_11/1/NIKOLOVA.pdf </a></p>
</div></div></div><div class="field field-name-field-related-faculty field-type-node-reference field-label-inline clearfix"><div class="field-label">Related Faculty: </div><div class="field-items"><div class="field-item even"><a href="/people/faculty/evdokia-nikolova">Evdokia Nikolova</a></div></div></div><div class="field field-name-field-tags field-type-taxonomy-term-reference field-label-inline clearfix"><div class="field-label">Keywords: </div><div class="field-items"><div class="field-item even"><a href="/tags/algorithmic-game-theory">Algorithmic Game Theory</a>, <a href="/tags/risk-aversion">Risk-aversion</a>, <a href="/tags/routing-under-uncertainty">Routing under uncertainty</a>, <a href="/tags/congestion">Congestion</a>, <a href="/tags/transportation-research">Transportation Research</a></div></div></div>Wed, 19 Mar 2014 21:32:03 +0000en47623412 at http://wncg.orghttp://wncg.org/research/briefs/traffic-assignment-uncertain-travel-times#commentsWNCG Part of Team Awarded $1.4 Million University Transportation Center Grant
http://wncg.org/news/wncg-part-team-awarded-14-million-university-transportation-center-grant
<div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"> <p>The <a href="http://wncg.org/" target="_blank">Wireless Networking and Communications Group</a> in the Department of Electrical and Computer Engineering at The University of Texas at Austin is part of a team that has been awarded a $1.4 million grant for the development of a Tier 1 University Transportation Center (UTC) by the USDOT’s Research and Innovative Technology Administration (<a href="http://www.rita.dot.gov/">RITA</a>) to advance cutting-edge research and educational programs that address critical transportation challenges facing our nation. WNCG is a co-beneficiary of the award along with the <a href="http://www.utexas.edu/research/ctr/" target="_blank">Center for Transportation Research (CTR</a>) at The University of Texas at Austin.</p>
<p>A $1.4 million grant will be given to form a national and international multimodal and multidisciplinary center that integrates innovative developments in “big data” analysis, wireless sensor networks, transportation planning and operations models, and intelligent transportation systems.</p>
<p>The faculty members from WNCG participating in D-STOP include Profs. Constantine Caramanis (ECE), Robert Heath (ECE), Todd Humphreys (ASE), Sriram Vishwanath (ECE), and Sanjay Shakkottai (ECE).</p>
<p><a href="http://ctr.utexas.edu/2013/10/16/utc-tier1/" target="_blank">Read more about this award</a></p>
</div></div></div><div class="field field-name-field-tags field-type-taxonomy-term-reference field-label-above"><div class="field-label">Keywords: </div><div class="field-items"><div class="field-item even"><a href="/tags/grant">Grant</a></div><div class="field-item odd"><a href="/tags/transportation-research">Transportation Research</a></div></div></div><div class="field field-name-field-publish-date field-type-datetime field-label-above"><div class="field-label">Publish Date: </div><div class="field-items"><div class="field-item even"><span class="date-display-single">Tuesday, October 22, 2013</span></div></div></div><div class="field field-name-field-image field-type-image field-label-above"><div class="field-label">Key Image: </div><div class="field-items"><div class="field-item even"><img src="http://wncg.org/sites/wncg.org/files/CTR-News-Graphic-2_1.jpg" width="350" height="250" /></div></div></div><div class="field field-name-field-related-faculty field-type-node-reference field-label-above"><div class="field-label">Related Faculty: </div><div class="field-items"><div class="field-item even"><a href="/people/faculty/robert-heath">Robert Heath</a></div><div class="field-item odd"><a href="/people/faculty/sanjay-shakkottai">Sanjay Shakkottai</a></div><div class="field-item even"><a href="/people/faculty/constantine-caramanis">Constantine Caramanis</a></div><div class="field-item odd"><a href="/people/faculty/sriram-vishwanath">Sriram Vishwanath</a></div></div></div><div class="field field-name-field-feature field-type-list-boolean field-label-above"><div class="field-label">Feature: </div><div class="field-items"><div class="field-item even">No</div></div></div>Tue, 19 Nov 2013 19:10:59 +0000carrat362 at http://wncg.orghttp://wncg.org/news/wncg-part-team-awarded-14-million-university-transportation-center-grant#comments