Session 38 Xiaoliang Ma
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Toward Integrated Traffic and Emission Impact Simulation: A Microscopic
Approach
Xiaoliang Ma, Ph.D. Centre for Traffic Research, KTH, Sweden
Zhen Huang, PhD candidate, Centre for Traffic Research, KTH, Sweden
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IntroductionThe skyrocketing of motor vehicle numbers leads to serious challenge to urban environment;
Different concerns of traffic emissions:
a) Highly dependent on fossil fuelsb) Green house gases (GHG) e.g. CO2c) Local air quality: CO, HC, NOx, PMetc.
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Policy and MeasureLong term: revolution on vehicle engine
and alternative fuel technologies;Middle to short terms: a) Management at the network level e.g. congestion
chargingb) Local traffic measures: signal, speed limit, traffic
calming… c) New Intelligent Transportation Systems
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Traffic emission impact modeling
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Traffic models:Macroscopic(Mesoscopic)Microscopic
Traffic and emission models
• Emission models▫ Aggregate emission models: MOBILE, COPERT IV, “ARTEMIS” ▫ Microscopic emission models:CMEM, VT-Micro, EMIT, POLY…
Vehicle dynamic emission, g/sec(Dynamic, instantaneous, local network)
Aggregate emission of a fleet, g/km(Main: Static, long-term, regional network)(Some: dynamic, shorter term)
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Research questions (1)Assessing traffic emissions (microscopic).
Lack of emission calculation software tool: well integrated with traffic models and can estimate emission at different resolutions ;
Difficulties to analyze and visualize traffic emissions and air quality impacts in time and space
Traffic Simulation Model
Traffic Simulation Output
Emission ModelEmission Output
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Research questions (2)Microscopic emission models becomes more and more
important for traffic operation and management
Microscopic emission calibration requires lots of data: complex and expensive to measure
Research question: How to calibrate microscopic emission models when
the emission measurements are not fully available?
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Research objectivesDevelop a systematic approach to integrate
traffic simulation models and emission models.
Develop a “calibration” method for microscopic emission models based on existing aggregate measures
Evaluation and optimizing traffic measures with respect to traffic emissions.
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MODENA Computational User Case
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Distributed implementation (Service)
Better PerformanceBoth traffic simulation and emission calculation are
computational expensive processesDecentralize these into different CPU processes or threads
Systematic DesignConcurrencyReliabilityIndependency
Plenty of implementationCORBAWeb Service (XML)Protocol buffers
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Model Calibration Method•Basic idea: calibrate microscopic emission model based on the aggregate emission measure at a rougher resolution on both time and space.
•Optimization objectives
Aggregate emission
Microscopic emission
Time interval
Sub network
Reference parameter
Penalty weight
Time stamp (sec)
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Numerical Implementation
Microscopic Emission Model VT-Micro is calibrated using aggregate estimation of ARTEMIS as reference.
Newton-reflective, Finite Difference Method (FDM), Simultaneous Perturbation Stochastic Approximation (SPSA) are adopted as optimization algorithms.
MAPE and MSE were used to validate model
performance.
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Model validation
Vehicletype
MAPE(%)
MSE
CO HC NOx CO HC NOx
Euro.I 3.33 5.05 4.66 24.0859 0.3588 0.4245
Euro.II 0.93 0.46 7.73 0.0655 1.55E-4 0.5752
Euro.III 9.13 28.63 4.40 2.4155 15.9782 0.2715
Euro.IV 7.02 3.72 6.97 0.2402 3.60E-4 0.0276
validation results for petrol cars
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Applications(1)-traffic demand
A road network in Stockholm: Fleminggatan
Major traffic flow runs W-E Various travel demands were evaluated by the calibrated microscopic emission model to assess the environmental impactsunder different congestionconditions.
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Applications(1)-traffic demand Three levels of traffic demands are applied:
Low – 75% of normal traffic demand;
Medium – normal traffic demand;
High – 125% of normal traffic demand.
1 hour simulation
Emission are computed in 10 min time interval
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Applications(2)-signal control An isolated signalized intersection
Major traffic flow runs W-E
Fixed stage signal controller is applied
Two signal plans are evaluated with calibrated emission model to assess environmental impacts
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Applications(2)-signal control
Signal Plan 1
Signal Plan 2
CO(g) 767.8 772.0
HC(g) 91.5 92.9
NOx(g) 185.3 185.1
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ConclusionAn emission estimation software platform is
developed by integrating traffic simulation model and emission model in a distributed way;
A numerical approach is proposed for calibration of microscopic emission models based on aggregate emission measures;
Case studies (evaluation and optimization of local traffic measures)
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Future WorkThe system will be developed as a web service
The calibration approach can be applied to other microscopic emission models or by using various aggregate measures
Application for improving various traffic measures and ITS systems: dynamic speed limits, vehicle based ITS systems etc.
Supporting mesoscopic emission model development in the new MEMFIS project
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Thank youQuestions?