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The impact of centroid connectors on transit assignment outcomes
- Original Paper
- Published: 20 August 2020
- Volume 12 , pages 611–629, ( 2020 )
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- Ouassim Manout ORCID: orcid.org/0000-0002-7688-7934 1 , 2 ,
- Patrick Bonnel 1 &
- François Pacull 3
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In transit modeling, access and egress conditions are often overlooked. The most common modeling technique of these conditions relies on the use of centroid connectors. This definition often uses the geographic position of zone centroids and sets constraints on the maximum number and length of connectors. This definition is subject to spatial aggregation issues and has already been proven to bias car assignment outcomes. The impact on transit assignment outcomes has not yet been demonstrated. The current paper investigates the statistical impact of connectors on transit assignment outcomes in an urban model of Lyon in France. Findings suggest that transit ridership, total passenger-kilometers and transit transfers are dependent on the definition of centroid connectors. Setting arbitrary values for the maximum number and length of connectors statistically affects transit results. The pattern and magnitude of this impact vary, however, between transit modes. The bus and rapid bus systems have been shown to be more sensitive towards the definition of connectors than the subway and the light rail systems. These findings question, to a certain extent, the validity and reliability of transit modeling outcomes.
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In fact, the calibration of transportation models often relies on “fine-tuning” the definition of connectors. In our case, this practice would mask the impact of the definition of centroid connectors on assignment outcomes.
Onboard Travel Surveys were conducted by the local transit authority between 2012 and 2016.
A trip is considered here as a travel, journey or movement between an origin and a destination using a specific travel mode or a combination of modes.
The Gaussian form is derived from a Gaussian Kernel-density estimation (KDE) method.
For these zones, all their centroid connectors are drawn but not necessarily used. Travel demand is distributed between connectors that produce shortest travel strategies.
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Acknowledgements
The authors are grateful to the reviewers of this paper. Their valuable comments and suggestions have contributed to the final version of this paper.
This work has been funded by ForCity, Agence Nationale de la Recherche et de la Technologie (ANRT), and Laboratoire Aménagement Economie Transports (LAET) under the CIFRE funding Grant no. 2015/0341. This financial support is gratefully acknowledged.
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Ouassim Manout & Patrick Bonnel
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Manout, O., Bonnel, P. & Pacull, F. The impact of centroid connectors on transit assignment outcomes. Public Transp 12 , 611–629 (2020). https://doi.org/10.1007/s12469-020-00246-w
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Accepted : 06 August 2020
Published : 20 August 2020
Issue Date : October 2020
DOI : https://doi.org/10.1007/s12469-020-00246-w
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On Centroid Connectors in Static Traffic Assignment: Their Effects on Flow Patterns and How to Optimize
In this paper, the authors investigate to what extent the results of static traffic assignment (STA) are influenced by centroid connectors and how to optimize their selections. Three networks are used to evaluate the impact of different centroid connector configurations on the resulting traffic flow pattern: a synthetic grid network, the California SR-41 corridor network and a large Sacramento area network. From the STA results of these three networks, the authors observe large fluctuations on resultant link volumes, maximum volume capacity (V/C) ratios, average V/C ratios and total travel time with respect to randomized connector selections. The fluctuations seem to indicate that STA results are unstable with respect to arbitrary connector selections, and this cannot be improved by simply increasing the number of connectors. In fact, more connectors often result in serious under-estimation of total travel time and average link load. The authors infer that, if provided little information of access/egress nodes of trips, randomly generated connectors lead to artificial over- or under-utilization on network links. The authors therefore propose a connector optimization algorithm in which the connectors and their travel times are chosen in such a way that the maximum V/C ratio of some characteristic links, ``direct links'', is minimized. As the numerical example on the SR-41 network indicates, this connector optimization algorithm seems to reduce the artificial over- and under-utilization of network links, and obtain a flow pattern more consistent with the one derived from a more refined network where trip access/egress nodes are known in more details.
Transportation Research Board
- Zhang, H Michael
- Transportation Research Board 89th Annual Meeting
- Location: Washington DC, United States
- Date: 2010-1-10 to 2010-1-14
- Media Type: DVD
- Features: Figures; Maps; References;
- Pagination: 22p
- Monograph Title: TRB 89th Annual Meeting Compendium of Papers DVD
Subject/Index Terms
- TRT Terms: Highway capacity ; Highway operations ; Optimization ; Traffic assignment ; Traffic flow ; Traffic volume ; Travel time
- Uncontrolled Terms: Static traffic assignment (STA)
- Geographic Terms: Sacramento (California)
- Subject Areas: Highways; Operations and Traffic Management; I71: Traffic Theory;
Filing Info
- Accession Number: 01154410
- Record Type: Publication
- Report/Paper Numbers: 10-2887
- Files: TRIS, TRB
- Created Date: Apr 14 2010 7:14AM
IMAGES
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In assignment it is first necessary to describe the transport network to which trips are being assigned. The network is described as a series of nodes .and con necting links; in a highway network the nodes would be the junctions and the links the connecting highways. Centroids of traffic zones, at which it is assumed that all
Recently, subarea traffic assignment was proposed to reduce the effect of centroid connectors on assignment results (Mann, 2002). In that study, up to 12 subzones are created automatically within each traffic zone, and the trip table is subdivided according the new "subzones".
In a comprehensive research conducted by Chang et al. , the authors find out that traffic assignment outcomes are dependent on the definition of zone centroids, and thus on the definition of centroid connectors. Four different configurations of centroid connectors are tested and explored in a statewide model of Idaho, USA.
Traffic assignment is the process by which a set of trip desires (a matrix of zone to zone interchanges) is allocated to a represen tation of the transportation network in a rational and orderly way. Land areas are aggregated into zones and all trips are assumed to originate and terminate at the zone centroid.
For this reason, centroid connectors could have significant impacts on the main outputs of transport models and particularly on the outcome of the traffic assignment procedure ( Chang et al., 2002 ...
Three strategies to improve the computational efficiency of path‐based algorithms for solving the static user equilibrium traffic assignment problem (STA) by providing a simple method to preclude the through‐routing via the zone centroid and helping to avoid unrealistic flow without affecting the flow update process of a PBA are proposed.
Advanced traffic assignment models, such as simulation-based dynamic traffic assignment, typically incorporate more detailed network representations than do traditional planning models. ... On Centroid Connectors in Static Traffic Assignment: Their Effects on Flow Patterns and How to Optimize Their Selections. Transportation Research Part B ...
Assignment of Centroids A centroid represents the "center of activity" of a TAZ and is used as the specific location of the origin and destination for all trips to and from the TAZ. A centroid may be a city, a town, or a ... number of centroid connectors on traffic demand forecast. As mentioned earlier, a centroid may.
In this paper, the authors investigate to what extent the results of static traffic assignment (STA) are influenced by centroid connectors and how to optimize their selections. Three networks are used to evaluate the impact of different centroid connector configurations on the resulting traffic flow pattern: a synthetic grid network, the ...
centroid connectors that improves on the "nearest node" paradigm. The goal of automating the process is to better enable the transi- tion between static traffic assignment models and dynamic ...