Stochastic user equilibrium assignment with traffic-responsive signal control

This paper considers the Stochastic User Equilibrium (SUE) assignment problem for a signal-controlled network in which intersection control is flow-responsive. The problem is addressed within a Combined Traffic Assignment and Control (CTAC) modeling framework, in which the calculation of user equilibrium link flows is integrated with the calculation of consistent signal settings [1]. It is assumed that network equilibrium is dispersed due to user misperceptions of travel times, and that the intersection control system is designed to allow the persistent adjustment of signal settings in response to traffic flow variations. Thus, the model simulates real- world situations in which network users have limited information and signal control is traffic-actuated. The SUE- based CTAC model is solved algorithmically by means of the so- called Iterative Optimization and Assignment (IOA) procedure, a widely used heuristic which relies on the alternate execution of a control step (signal setting calculation for fixed link flows) and an assignment step (network equilibration under fixed signal settings). The main objective of the study is to define a methodological framework for the evaluation of the performance of various traffic-responsive signal control strategies in interaction with different levels of user information, as represented by the spread parameter of the perceived travel time distribution assumed in the SUE assignment submodel. The results are of practical relevance in a policy context, as they provide a basis for assessing the potential integration of Advanced Traveler Information Systems (ATIS) and signal control systems. Several computational experiments are carried out on a small, contrived network and using realistic intersection delay functions, in order to test the behavior of the model under a wide range of conditions; in particular, convergence pattern and network performance measures at equilibrium are analyzed under alternative information/control scenarios and for various demand levels. The issue of uniqueness of the model solution is addressed as well. Reference: [1] Meneguzzer C. (1997). Review of models combining traffic assignment and signal control. ASCE Journal of Transportation Engineering, vol. 123, no. 2, pp. 148-155.

Analysis and control of the interaction between vehicular and pedestrian flows on roundabout approaches

This study considers the problem of estimating the reduction of roundabout entry capacity caused by pedestrian zebra crossings. An empirical procedure is developed on the basis of field observations collected at an urban four-leg roundabout located in Padova (Italy). The disturbance caused by pedestrians to approaching traffic is measured using crosswalk occupancy times, rather than pedestrian volumes like in previous studies. The proposed method leads to the determination of a capacity reduction index, which can be applied in operational analyses to obtain realistic estimates of roundabout entry capacities taking into account the impact of pedestrian crossings. Also, the possible effect of introducing pedestrian-actuated signal control on zebra crossings is evaluated, using simulation, with reference to alternative pedestrian volume and signal timing scenarios

Gap-acceptance behavior at roundabouts: validation of a driving simulator environment using field observations

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Before-and-After Field Investigation of the Effects on Pollutant Emissions of Replacing a Signal-Controlled Road Intersection with a Roundabout

The purpose of this study is to assess the effects on air pollution that may derive from replacing a signal-controlled intersection with a roundabout, using a before-and-after approach. Based on field data collected with a test car instrumented with a Portable Emission Measurement System, the two intersection configurations were compared in terms of emissions of CO2, CO, and NOX. The existence of significant differences in emissions between the two types of control was assessed by means of a statistical technique known as two-sample biaspect permutation test. In addition, focusing on trips carried out in peak traffic conditions, binary logistic regression models were developed to identify the factors that significantly affect vehicular emissions and to quantify their effect. The findings of our analyses show that emissions of CO2 and CO are generally lower for the roundabout than for the signal-controlled intersection, while an opposite result arises for NOX emissions. As far as other influential factors are concerned, trip direction (reflecting site-specific conditions) and driver behavior have a considerable impact on the emissions of all three pollutants

comparison of exhaust emissions at intersections under traffic signal versus roundabout control using an instrumented vehicle

Abstract The traditional approach to the comparison of alternative types of road intersection control has focused mainly on efficiency and safety. In recent years, the increasing importance of air pollution produced by vehicular traffic has suggested that environmental considerations should be added to the above aspects as a criterion for intersection design. This study describes a before-and-after analysis conducted on a road intersection where a roundabout has replaced a traffic signal. Using a Portable Emission Measurement Systems (PEMS) installed on a test car, the instantaneous emissions of CO2, NOX and CO have been measured over repeated trips along a designated route. A total of 396 trips have been carried out in different traffic conditions and in opposite directions along the chosen route. Using statistical methods the existence of significant differences in emissions attributable to the type of intersection control has been investigated based on the experimental data. The results indicate that replacing the traffic signal with the roundabout tends to reduce CO2 emissions, even if the differences are not always statistically significant; on the contrary, the signalized intersection performs better in terms of NOX emissions. Finally, results are less clear for CO emissions, and differences are statistically non significant in most cases

on road measurement of co2 vehicle emissions under alternative forms of intersection control

Abstract The environmental impact of road intersection operations, and in particular of alternative types of traffic control, has received increasing attention in recent years as a factor to be considered in addition to efficiency and safety. The purpose of this study is to provide experimental evidence about this issue based on direct measurement of CO2 emissions produced by a vehicle under traffic signal versus roundabout control. Carbon Dioxide was chosen as specific target of the analysis because of its important contribution to the "greenhouse effect". Using data collected with a Portable Emission Measurement System (PEMS) installed on a test car, a before-and-after analysis was conducted on an intersection where a roundabout has replaced a traffic signal. A total of 396 trips were carried out by two drivers in different traffic conditions and in opposite directions along a designated route. Using statistical methods, the existence of significant differences in CO2 emissions in relation to the type of intersection control was investigated based on the collected data, also considering the effect of other explanatory variables and focusing in particular on peak traffic conditions. More precisely, the effect of the type of control has been characterized using descriptive statistics and permutation tests applied to the entire data set, while an analysis based on binary logistic regression has been performed with specific reference to trips carried out under peak traffic conditions. The results of these analyses support the conclusion that converting a signal-controlled intersection to a roundabout may lead to a decrease in CO2 emissions

Flussi, code e reti: elementi di analisi dei sistemi di trasporto

"Flussi, code e reti" introduce il lettore all\u2019ingegneria dei sistemi di trasporto, delineando i principi generali della disciplina e presentando un\u2019esposizione elementare di alcune teorie fondamentali su cui si basa l\u2019analisi funzionale dei sistemi stessi: la teoria del deflusso veicolare, la teoria delle code e la teoria dei grafi e delle reti. Vengono inoltre trattate due tematiche che si possono considerare \u201ctrasversali\u201d rispetto alle suddette teorie: l\u2019approccio probabilistico allo studio dei sistemi di trasporto e l\u2019analisi dei costi d\u2019uso e dei tempi di percorrenza di singoli elementi di una rete di trasporto. L\u2019esposizione degli argomenti trattati \ue8 corredata di esempi di applicazione, che hanno lo scopo di aiutare il lettore a consolidare la comprensione dei contenuti teorici. Il volume \ue8 pensato come testo di riferimento per un corso universitario di base nel campo dell\u2019ingegneria dei sistemi di trasporto, e pu\uf2 inoltre costituire un utile strumento di consultazione per studiosi, tecnici e professionisti che desiderino avvicinarsi alle tematiche fondamentali dell\u2019analisi funzionale dei sistemi di trasporto o ampliare le proprie conoscenze in materia

Capacity implications of equilibrium traffic signal setting under stochastic route choice

A simple modelling framework for the assessment of the capacity implications of Equilibrium Traffic Signal Setting is presented and tested on a small network. The main conclusions of the study are that network capacity is mostly affected by the signal-setting policy, and that providing information to all drivers does not necessarily improve system performance