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?