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A Portfolio Theory of Route Choice

PortfolioTheory

Recently published:

Although many individual route choice models have been proposed to incorporate travel time variability as a decision factor, they are typically still deterministic in the sense that the optimal strategy requires choosing one particular route that maximizes utility. In contrast, this study introduces an individual route choice model where choosing a portfolio of routes instead of a single route is the best strategy for a rational traveler who cares about both journey time and lateness when facing stochastic network conditions. The proposed model is compared with UE and SUE models and the difference in both behavioral foundation and model characteristics is highlighted. A numerical example is introduced to demonstrate how such model can be used in traffic assignment problem. The model is then tested with GPS data collected in metropolitan Minneapolis–St. Paul, Minnesota. Our data suggest there is no single dominant route (defined here as a route with the shortest travel time for a 15 day period) in 18% of cases when links travel times are correlated. This paper demonstrates that choosing a portfolio of routes could be the rational choice of a traveler who wants to optimize route decisions under variability.


JEL-Code: R41, R48, D63
Keywords: Transportation planning, route choice, travel behavior, link performance

Route


In my lab today we had a discussion over the proper way to say the word "Route" dictionaries and professional linguists who were consulted give both "root" and "rout" as acceptable pronunciations, leaving us no wiser than before.

But online, we find this Dialect survey (color matching the map).


Dialect Survey Results:


"26. route (as in, "the route from one place to another") 
     a. rhymes with "hoot" (29.99%)
     b. rhymes with "out" (19.72%)
     c. I can pronounce it either way interchangeably (30.42%)
     d. I say it like "hoot" for the noun and like "out" for the verb. (15.97%)
     e. I say it like "out" for the noun and like "hoot" for the verb. (2.50%)
     f. other (1.40%)
     (11137 respondents)"




As a north-easterner myself, It was always take Root 29 or Root 95, but in the South, we were on Rout 85. In the midwest, it seems more Rout than Root. In any case the "e" is superfluous, as it doesn't modify in a consistent way, since we already have a double vowel. The word is also superfluous, since we already have the word "road" from the same root. Damn French imports.

Etymology online says: route (n.) early 13c., from O.Fr. rute "road, way, path," from L. rupta (via) "(a road) opened by force," from rupta, fem. pp. of rumpere "to break" (see rupture). Sense of "fixed or regular course for carrying things" (cf. mail route) is 1792, an extension of the meaning "customary path of animals" (early 15c.).

See also this on Highway Linguistics

ShortestPath

Working paper:



Most recent route choice models, following either the random utility maximization or rule-based paradigm, require explicit enumeration of feasible routes. The quality of model estimation and prediction is sensitive to the appropriateness of the consideration set. However, few empirical studies of revealed route characteristics have been reported in the literature. This study evaluates widely applied shortest path assumption by evaluating morning commute routes followed by residents of the Minneapolis - St. Paul metropolitan area. Accurate GPS and GIS data were employed to reveal routes people used over an eight to thirteen week period. Most people do not choose the shortest path. Using three weeks of that data, we find that current route choice set generation algorithms do not reveal the majority of paths that individuals took. Findings from this study may provide guidance for future efforts in building better route choice models.



JEL-Code: R41, R48, D63

Keywords: Transportation planning, route choice, travel behavior, link performance

A Portfolio Theory of Route Choice

PortfolioTheory


Working paper:

  • Zhu, Shanjiang and David Levinson (2010), A Portfolio Theory of Route Choice Presented at 4th International Symposium on Transportation Network Reliability, July 2010, Minneapolis, MN.

Although many individual route choice models have been proposed to incorporate travel time variability as a decision factor, they are typically still deterministic in the sense that the optimal strategy requires choosing one particular route that maximizes utility. In contrast, this study introduces an individual route choice model where choosing a portfolio of routes instead of a single route is the best strategy for a rational traveler who cares about both journey time and lateness when facing stochastic network conditions. The model is then tested with GPS data collected in metropolitan Minneapolis-St. Paul, Minnesota. Our data suggest strong correlation among link speed when analyzing morning commute trips. There is no single dominant route (defined here as a route with the shortest travel time for a 15 day period) in 18% of cases when links travel times are correlated. This paper demonstrates that choosing a portfolio of routes could be the rational choice of a traveler who wants to optimize route decisions under variability.



JEL-Code: R41, R48, D63

Keywords: Transportation planning, route choice, travel behavior, link performance


John Adams, Shanjiang Zhu, and David Levinson

Congratulations to soon-to-be Dr. Shanjiang Zhu (September 2010- PhD Civil Engineering) for completing and successfully defending his Ph.D Dissertation -
The Roads Taken: Theory and Evidence on Route Choice in the wake of the I-35W Mississippi River Bridge Collapse and Reconstruction He will be joining the University of Maryland, College Park as a post-doc.

Abstract:


Route choice analysis investigates the path travelers follow to implement their travel plan. It is the most frequent, and thus arguably the most important decision travelers make on a daily basis. Long established efforts have been dedicated to a normative model of the route choice decision, while investigations of route choice from a descriptive perspective have been limited. Wardrop's first principle, or the shortest path assumption, is still widely used in route choice models. Most recent route choice models, following either the random utility maximization or rule-based paradigm, require explicit enumeration of feasible routes. The quality of model estimation and prediction is sensitive to the appropriateness of the consideration set. However, few empirical studies of revealed route characteristics have been reported in the literature. Moreover, factors beyond travel time, such as preferences for travel time reliability, inertia in changing routes, and travel experience that could also have significant impacts on route choice, have not been fully explored and incorporated in route choice modeling. The phenomenon that people use more than one route between the same origin and destination during a period of time is not addressed by conventional route choice models either.

To bridge these gaps, this dissertation systematically evaluates people's route choice behavior using data collected in the Minneapolis - St. Paul metropolitan area after the I-35W Bridge Collapse. Both aggregate traffic data and individual survey data show gaps between models based on shortest travel time assumption and traffic conditions observed in the field. This study then employs the individual GPS trajectory and GIS maps to systematically evaluate the characteristics of routes people actually use. Merits of route choice set generation algorithms widely used in practice are assessed. The phenomenon of route diversity is clearly revealed through analysis of field data. A route portfolio model is proposed to explain the rationale of choosing a portfolio of routes under uncertainty about network conditions. It is posited that a rule-based model,
comprehensively considering travelers' characteristics, additional network metrics, and previous travel experience will better replicate observed route choices than the tradi- tional assumption of simply minimizing travel time or travel cost. Findings from this dissertation could also inform other parts of travel demand modeling.

Bill St. Arnaud finds: The Flattening Internet Topology: Natural Evolution, Unsightly Barnacles or Contrived Collapse? by Phillipa Gill, Martin Arlitt, Zongpeng Li, and Anirban Mahanti. The full article can be found here (pdf).


In this paper we collect and analyze traceroute measure- ments1 to show that large content providers (e.g., Google, Microsoft, Yahoo!) are deploying their own wide-area networks, bringing their networks closer to users, and bypassing Tier-1 ISPs on many paths. This trend, should it continue and be adopted by more content providers, could flatten the Internet topology, and may result in numerous other consequences to users, Internet Service Providers (ISPs), content providers, and network researchers.

First slugs, now oil

From DK:

For your blog since you've been keeping up with the slugs predicting roadways, here is a story of a drop of oil that solves a maze. I'm not sure what happens if the slugs get their hands on the oil, but there seems to be some spurious lesson about intelligence from these stories. What a maze-solving oil drop tells us of intelligence (New Scientist)
David Levinson

Network Reliability in Practice

Evolving Transportation Networks

Place and Plexus

The Transportation Experience

Access to Destinations

Assessing the Benefits and Costs of Intelligent Transportation Systems

Financing Transportation Networks

View David Levinson's profile on LinkedIn

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