DEVELOPMENT OF A HYBRID TRAFFIC SIMULATION FRAMEWORKFOR ENVIRONMENTAL EVALUATION FOR ITS APPLICATIONS

Hisatomo Hanabusa, Tomoyoshi Shiraishi, Katsuaki Koide, Ryota Horiguchi
i-Transport Lab. Co., Ltd.
3F, Jimbocho 1-4BLDG, Kanda Jimbocho 1-4, Chiyoda-ku, Tokyo, Japan 101-0051+81-3-5283-8527,{hanabusa|shiraishi|koide|rhoriguchi}@i-transportlab.jp
Shinji Tanaka, Masao Kuwahara
Institute of Industrial Science, University of Tokyo
4-6-1 Komaba, Meguro-ku, Tokyo, Japan 153-8505+81-3-5452-6419, {stanaka|kuwahara}@iis.u-tokyo.ac.jp
Takashi Oguchi, Hiroyuki Oneyama
Tokyo Metropolitan University
1-1 Minami-Osawa, Hachioji-shi, Tokyo, Japan 192-0397+81-426-77-2780,{oguchi|oneyama}@tmu.ac.jp

ABSTRACTThe purpose of this paper is to introduce the development of a hybrid traffic simulation
framework (HTSF) to evaluate ITS applications with CO2 emissions. This study is a part ofour themes in the Energy ITS Project, and we developed the prototype using this framework
harmonized with CO2 emission model (EM). The HTSF provides a simulation environment tocombine three traffic simulation models in different resolutions. ITS applications should beevaluated comprehensively because there are many ITS applications which have different
scales of impact. Therefore, the HTSF in this study is considered that the output of CO2
emissions including a variety of impacts from ITS applications can be estimated for the target
area. This study is a part of the researches in the Energy ITS project organized by NEDO(New Energy and technology Development Organization) in Japan.

BACKGROUNDFirst of all, we introduce the background of this study before the concept of the HTSF. Oneof the major topics in the Energy ITS project is to establish the rational procedure to estimate
CO2 emissions from automobiles. The Energy ITS project has been started in 2008, and we-1-

have been discussed about the evaluation procedure of ITS applications toward the goal of theproject in our international collaboration scheme with EU and US partners. Fig.1 shows theresearch directories to establish the estimation method in the Energy ITS project.(1) In thestudy of the HTSF, we work on the traffic simulation technologies that can evaluate
quantitatively ITS applications to reduce CO2 emissions in automobile traffic. In addition, therequirements for the traffic simulation technologies to output the rational result of CO2emissions are discussed. After that, we develop the HTSF and the evaluation tool using theHTSF.

Fig.1 Research directories to establish the estimation method in the Energy ITS project

CONCEPT OF THE HYBRID TRAFFIC SIMULATION FRAMEWORKHybrid traffic simulation which considered the combination of the different types of TSs
has been already discussed by some research. (2)(3)(4) And it is believed that the evaluationof CO2 emissions using traffic simulation model is generally accepted. However, we should
point out here that existing models by the combination of TS and EM are not considered theeffect to CO2 emissions by ITS applications. It is said that validation result of TS with EM israrely found. The HTSF in this study is intended to evaluate ITS application which isexpected to reduce CO2 emissions. Therefore, the result of CO2 emissions by the traffic
simulation considering to the interactions of the impact on a macro scale and on a micro scaleis required for the goal of this study. Furthermore, the verification and validation process are
an important point for the reliable and quantitative evaluation. The HTSF in the Energy ITS
project is developed based on the following keywords.
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Enlargement: to cover the whole Japan road network with mesoscopic TS for nation-widecase studies and to cut out partial networks for regional studies and give them baseconditions (e.g. OD matrix) easily.
Partial refinement: to embed a microscopic TS into a mesoscopic TS to reproduce finegrained traffic conditions when it is necessary.
Real time: to monitor the present traffic conditions and CO2 emissions by using real-timeprobe data.

“Enlargement” means the concept about the area scale for traffic simulation. The HTSF
provides a capability to be able to simulate the arbitrary area as a part of a large-scaled traffic
simulation network. “Partial refinement” describes the concept about the integration ofdifferent modeling levels of TSs. For example, a microscopic TS handle a part of an area
represented by a mesoscopic TS with ITS Applications which are needed to handle detailed
behaviors of vehicles. “Real time” is explained that the traffic condition can be represented inreal time using the HTSF for the monitoring of CO2 emissions. Fig.2 shows an image of theevaluation tool concept using the HTSF. First, ITS applications are modeled according torequirements for evaluation such as area scale and installed to each simulation models. Afterthe installation, those applications are simulated by traffic simulators at different levels oftraffic flow model in parallel when it is necessary. In this simulation, these simulators
exchange the simulation result such as vehicle movements with route choices, traffic volumes
and link travel times for every scan. Therefore, each simulation model on the HTSF can give
traffic impacts with each other. And EM can be incorporated to estimate CO2 emissions fromthe simulation results. Fig.3 shows the evaluation image using the HTSF.

Fig.2 An image of the evaluation tool concept using the HTSF-3-

Fig.3 the evaluation image using the HTSF
Fig.4 shows the integration example of TSs using the HTSF. In this simulation, the vehicle
information with vehicle ids, positions, current speeds and other attributes is shared by each
TS on the HTSF. Vehicles in the simulation choose their routes considering a whole of thesimulation network. The issues we discuss are the method of the model combination to solve
the problem of the boundary condition between different traffic models.

Fig.4 the vehicle moving by integrated models on the HTSF
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TRAFFIC SIMULATIONS FOR THE INTEGRATIONIn this study, we use the following TSs for the integration. Fig.5 shows the traffic simulation
models for the integration on the HTSF.
SOUND(5) : mesoscopic TS for region-wide road network
AVENUE(6) : mesoscopic TS for city-wide road network
MicroAVENUE : microscopic TS for the requirement for more detailed vehicle behavior.

SOUND is a mesoscopic TS that vehicle is moved by the queuing model based on theSimplified Kinematic Wave Theory(7)(8). AVENUE employs the Hybrid Block Density
Method (HBDM) (6). HBDM is the traffic flow model which treats traffic flow as continuum.
MicroAVENUE is a microscopic TS based on the car following model that the speed ofvehicle is determined by the target headway with some parameters such as target speed, max
acceleration.

Fig.5 Traffic simulation models for the integrate on the HTSF-5-

INTERFACE BETWEEN TS AND EM (STEPWISE SPEED FUNCTION)
To estimate CO2 emissions by the harmonization of TS and EM, there are many
combinations of TS and EM. Fig.6 shows the combinations between TS and EM. Three typesof vehicle trajectory of TS can generally be divided as shown by Fig.6. Link-wised linear
trajectory is drawn based on link enter time and link exit time. However it is difficult that theacceleration points and the deceleration points can be understood. Fine grained trajectory is
the most detailed data that the acceleration pattern can be calculated at high resolution.
However, fine grained trajectory cannot be outputted by mesoscopic TS. State-wised linear
trajectory can be calculated by the both of TS types. The detailed vehicle behavior is notreferred, but the state of vehicle behavior (acceleration, running deceleration and stop) and its
position can be used as the interface with EM. On the other hand, EM can be chosen
according to the input data of TS. To evaluate ITS applications with CO2 emissions, the effectof the acceleration pattern by ITS should be considered because some of ITS applications (e.g.
support system of EcoDriving) are needed to control the driver’s acceleration pattern.
Therefore, we choose the combination of state-wised linear trajectory and developed Stepwise
Speed Function (SSF) as the interface between TS and EM from the point of view from thehybrid traffic simulation. And meso-scaled EM to harmonize with TS using the HTSF wasalso developed in the Energy ITS Project.

Fig.6 Combinations between TS and EM-6-Fig.7 shows the image of SSF. And Fig.8 shows the generation process of SSF. SSF has anaverage speed of vehicle from start to stop with the additional information which includes
number of acceleration, number of deceleration, road types (e.g. highway, regular road),longitudinal grade and etc. SSF is calculated by the trajectory of each vehicle in TS. SSF is
not only a simple and low-sized interface but also the acceleration can be considered in somelevel. Therefore, it is said that SSF is applicable for large size of simulation network toevaluate ITS applications. On the other hand, EM which has the interface for SSF
accumulates SSF pattern from the observed data using probe car in real word.

Fig.7 Stepwise Speed Function

Fig.8 Generation process of SSF-7-

For the implementation of SSF, we use TS and Map data base (DB) as shown in Fig.9. Firstly,vehicle trajectories are made with vehicle information in TS. Secondly, SSFs are generatedusing vehicle trajectories referring to Map DB. And finally, SSFs are used by EM to estimate
CO2 emissions. In this study, the additional information for SSF includes road type andlongitudinal grade. SSF is able to have more information from Map DB if other information isneeded to add to SSF.

Fig.9 Implementation of SSF for the harmonization of TS and EMVERIFICATION AND VALIDATION OF THE HTSF
The important point of the verification for the hybrid type of traffic simulation is that theshockwave propagation should be expressed based on traffic flow theory when the traffic
queue is spilled back from a bottleneck to upstream over the boundary between traffic models.
Fig.10 and Fig.11 shows a verification example using a simple network of the test case. The
shockwave of traffic can be checked by the vehicle trajectories over the boundary between
mesoscopic TS and microscopic TS. On the other hand, it is said that the continuity oftrajectories on the boundary should be verified, especially for EM.

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Fig.10 A case setting for the verification of the HTSF

Fig.11 A verification example using a simple network
On the other hand, the validation of each simulation models is done. As an example, thevalidation results of SOUND and AVENUE are disclosed on the website of ‘Traffic
Simulation Clearing House’ (http://www.jste.or.jp/sim/index.html). And the development ofvalidation manual for the evaluation tool integrated TS and EM have been discussed inEnergy ITS project (9). After the verification of our evaluation tool using the HTSF, thesimulation results such as traffic volume, vehicle trajectories and CO2 emissions are comparedwith our data set in Tokyo.

FUTURE WORKSIn this paper, we introduced the hybrid traffic simulation framework that integrates thedifferent types of TSs. We developed a prototype of evaluation tool for ITS Applications using-9-

the HTSF. As the future works, we practice some case studies of the evaluations of ITS
applications after the verification and validation. And the evaluation process of ITS
application is described through the case studies.

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