Agent-based modeling and simulation of individual traffic as an environment for bus schedule simulation

To re-establish the regular driving operations of a tram network, which was disturbed significantly by unforeseen external events, traffic schedulers apply rescheduling and rerouting strategies. These strategies are usually multi-modal; they consider the interaction of trams, buses, even taxis. Thus, to evaluate the applicability of a given rescheduling or rerouting strategy prior to its implementation in the real-world system, a multi-modal simulation software is needed. In this article we present an agent-based model of individual traffic which will be applied as background to a planned simulation of bus traffic. These combined models are to be integrated with an existing tram schedule simulation; the resulting multi-modal model will then be applied to evaluate the usefulness of given rescheduling or rerouting strategies. After a short introduction to agent-based modeling and simulation, as well as to existing models of individual traffic, this paper proposes to model the behavior of individual traffic as an environment for agent-based bus schedule simulation. Finally, some experiments are conducted by modeling and simulating individual traffic in Cologne's highly frequented Barbarossaplatz area

Agent-based modeling and simulation of individual traffic as an environment for bus schedule simulation

To re-establish the regular driving operations of a tram network, which was disturbed significantly by unforeseen external events, traffic schedulers apply rescheduling and rerouting strategies. These strategies are usually multi-modal; they consider the interaction of trams, buses, even taxis. Thus, to evaluate the applicability of a given rescheduling or rerouting strategy prior to its implementation in the real-world system, a multi-modal simulation software is needed. In this article we present an agent-based model of individual traffic which will be applied as background to a planned simulation of bus traffic. These combined models are to be integrated with an existing tram schedule simulation; the resulting multi-modal model will then be applied to evaluate the usefulness of given rescheduling or rerouting strategies. After a short introduction to agent-based modeling and simulation, as well as to existing models of individual traffic, this paper proposes to model the behavior of individual traffic as an environment for agent-based bus schedule simulation. Finally, some experiments are conducted by modeling and simulating individual traffic in Cologne's highly frequented Barbarossaplatz area

GTPase-specific binding to their effectors.

<p>A) Coomassie-stained SDS-gel of precipitates of pull down experiments from HEp2 cell lysate. Arrows indicate GST-Rac1/−Rac1 S71E (48 kDa) used as bait and a coprecipitated 190 kDa protein that was identified as IQGAP1 by MALDI-TOF/TOF analysis. B) The interaction of active, GTP-bound Rac1/Cdc42 and their active forms (Q61L) with specific effectors was analyzed by immunoblot analyses of precipitates from pull down assays. Non-specific binding was tested by GST-loaded glutathione beads as control. C) Representative input control of pull down analyses using constitutively active (Q61L) mutants of Rac1 and Cdc42 and their S71E mutants. D) Representative immunoblots of pull down precipitates showing the interaction of constitutively active Rac1 and Cdc42 and constitutively active S71E mutants with their effector proteins. Rac1 Q61L/S71E and Cdc42 Q61L/S71E did hardly bind to their specific effectors Sra-1 and N-WASP, respectively and to their common effector protein PAK1. Both phosphomimetic GTPases, however bound to their common effectors IQGAP and MRCK alpha, although to a lesser extent. The bars show the arithmetic mean value ± SD of densitometrical evaluation of 3 independent experiments.</p

Activation of PAK by Rac1 and Rac1 S71E.

<p>The effect of Rac1 and Rac1 S71E on PAK phosphorylation was shown in HEp2 cells stably expressing either GTPase. A) A brief characterization of these stable transfected cell lines was done by scanning electron microscopy showing surface topology of the cells. B) Immunoblot analysis revealed comparable ectopic expression of HA-tagged Rac1 and Rac1 S71E and concomitant Ser-144 phosphorylation of PAK1 and Thr-402 phosphorylation of PAK2. C) densitometrical evaluation of three separate Immunoblots showing phosphorylation of PAK 1/2. Shown are mean values ± SD. D) Propidium iodide staining of stable cell lines indicates populations of cells with 2n (G1 phase) or 4n (G2/M phase) set of chromosomes. Shown are percentages of cells within different cell cycle phases (mean values of five separate experiments).</p

Activity status of Rac1 S71E and Cdc42 S71E.

<p>A) Cell lysates of <i>Rac1^fl/fl</i> and <i>rac1</i>^−/− mouse fibroblasts were analyzed for Ser-71 phosphorylation of Rac1 and Cdc42 after treatment with 100 ng/ml EGF for 2 h by immunoblot using anti-pRac1/pCdc42 (Ser71) antibody. Lack of specific signal in <i>rac1</i>^−/− cells strongly suggested specific phosphorylation of Rac1 and no detectable phosphorylation of Cdc42. Immunoblot is representative for three separate experiments B) GTP-binding of phosphomimetic (▴) Rac1 S71E and Cdc42 S71E in comparison with wild-type (○) Rac1 and Cdc42 was analyzed by a [γ-³²P]-GTP-binding assay. The diagrams show mean values ± SD of three separate experiments. C) Intracellular localization of pRac1/pCdc42 (Ser71). Phosphorylated Rac1/Cdc42 is exclusively present in the membrane fraction of cells. D) Pull down assay of pRac1/pCdc42 and Rac1 using PAK-PBD after overexpression of Rho-GDI. Total Rac, total pRac1/pCdc42, and expression of Rho GDI were checked by immunoblot of whole cell lysate (lower panel). E) Pull down assay in a recombinant system showed nucleotide dependent binding of wild-type Rac1, Rac1 S71E and Rac1 S71A to the PAK-p21 binding domain. E) The nucleotide-dependent binding of Rac1, Rac1 S71E and Rac1 S71A to full length PAK1 as determined by pull down experiments with HEp2 cell lysates using GTPases as bait.</p

NF-κB is activated by phosphorylated Rac1.

<p>HEK 293 cells were co-transfected with NF-κB luciferase reporter plasmid as well as with Rac1 and Cdc42 mutants. Cells were lysed after 40 hours and analyzed for luciferase activity. Relative fold activity of mock-transfected cells is shown (arithmetic means±SD, n = 4). B) Expression of HA-tagged GTPases of quadruplicate samples from reporter gene assays was visualized by immunoblot using an anti-HA antibody.</p

Phosphomimetic Rac1 S71E induces filopodia formation.

<p>A) Treatment with 100 ng/ml EGF for 2 h induces pronounced formation of filopodia. Cells were stained for nuclei (DAPI, blue), actin cytoskeleton (rhodamin-phalloidin, red), and VASP (Alexa-488, green). B) HEp2 cells transfected with HA-tagged Rac1, Rac1 S71E, Cdc42, and Cdc42 S71E. Expression of GTPases was visualized by HA-staining, the actin cytoskeleton was stained with rhodamin-phalloidin. Only Rac1 S71E induced morphotype that is comparable with EGF-induced alterations. C) Phenotypes of HEp2 cells transfected with HA-tagged constitutive active mutants of Rac1 and Cdc42 as well as their phosphomimetic mutants S71E. Constitutively active (Q61L) Rac1 induced membrane ruffling whereas Rac1 S71E induced formation of filopodia. Filopodia formation is less pronounced in Cdc42 Q61L and Cdc42 Q61L/S71E transfected cells. Stained are nuclei (blue) and HA-tag (green); bar represents 10 µm. D) Active, GTP-bound form of Cdc42 was determined by G-LISA 24 h post transfection with constructs as indicated. Cdc42 Q61L was used for transfection experiments as positive control for experimental setup. Additionally, <i>C. difficile</i> toxin A (TcdA) was used as negative control for inactivation of Cdc42. The bar chart shows mean values ± SD of three (for TcdA) or four separate experiments.</p