TY - JOUR

T1 - Evaluating the assumption of independent turning probabilities

AU - Bar-Gera, Hillel

AU - Mirchandani, Pitu B.

AU - Wu, Fan

N1 - Funding Information:
The authors wish to thank David Boyce for reviewing several previous versions of this paper. The authors also like to acknowledge the US–Israel Binational Science Foundation grant #2002145 and the Federal Highway Administration Contract DTFH61-05-P-00104 for their partial support for this research. Suggestions by the reviewers of the paper are also appreciated.

PY - 2006/1/1

Y1 - 2006/1/1

N2 - Several urban traffic models make the convenient assumption that turning probabilities are independent, meaning that the probability of turning right (or left or going straight through) at the downstream intersection is the same for all travelers on that roadway, regardless of their origin or destination. In reality most travelers make turns according to planned routes from origins to destinations. The research reported here identifies and quantifies the deviations that result from this assumption of independent turning probabilities. An analysis of this type requires a set of reasonably realistic "original" route flows, which were obtained by a static user-equilibrium traffic assignment and an entropy maximization condition for most likely route flows. These flows are compared with those route flows resulting from the Assumption of Independent Turning Probabilities (ITP). A small subnetwork of 3 km by 5 km in Tucson, Arizona, was chosen as a case study. An overall "typical ratio" of 2.2 between original route flows and ITP route flows was obtained. Aggregating route flows to origin-destination flows led to an overall "typical ratio" of 1.7. Such deviations are particularly high for routes that go back-and-forth, reaching a ratio of more than 3 in certain time periods. Substantial deviations for origins and destinations that are on the same border of the subnetwork are also observed in the analyses. In addition, under the ITP assumption, morning rush hour traffic peaking is the same in all directions, while in the original flows some directions do not exhibit a peak in the morning rush hour period. Overall, the conclusion of the paper is that the assumption of independent turning probabilities leads to substantial deviations both at the route level and at the origin-destination level, even for such a small network of the case study. These deviations are particularly detrimental when a network is being modeled and studied for route-based measures of effectiveness such as the number and types of routes passing a point - for monitoring specified vehicles and/or managing detouring strategies.

AB - Several urban traffic models make the convenient assumption that turning probabilities are independent, meaning that the probability of turning right (or left or going straight through) at the downstream intersection is the same for all travelers on that roadway, regardless of their origin or destination. In reality most travelers make turns according to planned routes from origins to destinations. The research reported here identifies and quantifies the deviations that result from this assumption of independent turning probabilities. An analysis of this type requires a set of reasonably realistic "original" route flows, which were obtained by a static user-equilibrium traffic assignment and an entropy maximization condition for most likely route flows. These flows are compared with those route flows resulting from the Assumption of Independent Turning Probabilities (ITP). A small subnetwork of 3 km by 5 km in Tucson, Arizona, was chosen as a case study. An overall "typical ratio" of 2.2 between original route flows and ITP route flows was obtained. Aggregating route flows to origin-destination flows led to an overall "typical ratio" of 1.7. Such deviations are particularly high for routes that go back-and-forth, reaching a ratio of more than 3 in certain time periods. Substantial deviations for origins and destinations that are on the same border of the subnetwork are also observed in the analyses. In addition, under the ITP assumption, morning rush hour traffic peaking is the same in all directions, while in the original flows some directions do not exhibit a peak in the morning rush hour period. Overall, the conclusion of the paper is that the assumption of independent turning probabilities leads to substantial deviations both at the route level and at the origin-destination level, even for such a small network of the case study. These deviations are particularly detrimental when a network is being modeled and studied for route-based measures of effectiveness such as the number and types of routes passing a point - for monitoring specified vehicles and/or managing detouring strategies.

KW - Entropy maximization

KW - Markovian traffic flow models

KW - Route choice

KW - Turning proportions

KW - User-equilibrium

UR - http://www.scopus.com/inward/record.url?scp=33745854440&partnerID=8YFLogxK

U2 - 10.1016/j.trb.2006.01.001

DO - 10.1016/j.trb.2006.01.001

M3 - Article

AN - SCOPUS:33745854440

VL - 40

SP - 903

EP - 916

JO - Transportation Research, Series B: Methodological

JF - Transportation Research, Series B: Methodological

SN - 0191-2615

IS - 10

ER -