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
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
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.
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
Traffic emission impact modeling
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)
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
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?
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.
MODENA Computational User Case
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
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)
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.
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
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.
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
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
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
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)
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
Thank youQuestions?