Systems, Models, and Simulation. System

Lecture 1 P-1 Systems, Models, and Simulation System Experiment with the actual system Physical model Analytical solution Experiment with a mod...
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Lecture 1


Systems, Models, and Simulation


Experiment with the actual system

Physical model

Analytical solution

Experiment with a model of the system

Mathematical Model


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Traffic Simulation  Simulation models  Used to analyze a wide variety of dynamic problems which are not amenable to study by other means. Entity Entity Entity

Entity Entity System

 Often, the behavior of each entity and the interaction of a limited number of entities may be well understood and can be reliably represented logically and mathematically with acceptable confidence. But the complex, simultaneous interactions of many system components cannot, in general, be adequately described in mathematical or logical forms.  Simulation may be the only way to analyze such cases.  Simulation models integrate these separate entity behaviors and interactions to produce a detailed, quantitative description of system performance.  Simulation models “mimic” the behavior of such systems. Simulation models  mathematical/logical representations (or abstractions) of real-world systems, which take the form of software executed on a digital computer in an experimental fashion.

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What simulation models typically give?  First, the user of traffic simulation software specifies a “scenario” (e.g., highway network configurations, traffic demand, control strategy, etc.) as models.  The simulation model results describe system operations in two formats: o Statistical  The numerical results provide the analyst with detailed quantitative descriptions of what is likely to happen. o Graphical (and animated)  The graphical and animated representations of the system functions can provide insights so that the trained observer can gain an understanding of how the system is behaving in order to explain why the system is behaving this way (as described by the statistical, or numerical, results).  It is the responsibility of the analyst to properly interpret the wealth of information provided by the model to gain an understanding of cause-and-effect relationship.

This is very important!

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Wide range of applications  Evaluation of alternative treatments  Testing new designs  As an element of the design process  Embed in other tools (Transportation demand model may include a simulation module – like trip assignment)  Training personnel  Safety analysis

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Typical Simulation Output Statistics: MOEs (Table 10.1 of Chapter 10, Revised Monograph on Traffic Flow Theory )

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Classification of Simulation Models  Time is always the basic independent variable used to describe dynamic systems by traffic simulation models.

 Continuous vs. Discrete simulation models o o

Continuous  describe how the elements of a system change state continuously over time in response to continuous stimuli Discrete  represent real-world systems (either continuous or discrete) by asserting that their states change abruptly at points in time.

 Simulation classification by how events occur: o Discrete time (traffic software programs are typically this type because vehicles are continuously moving.) o Discrete event (plant operation, bank-teller analysis  nothing that changes state happens between the events)  Simulation classification by the level of detail with which they represent the system to be studied

o Microscopic (high fidelity) o Mesoscopic (mixed fidelity) o Macroscopic (low fidelity)  Simulation classification o Deterministic o Stochastic (Random numbers)

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Signal Optimization/Simulation Models Supported by the Federal Highway Administration Optimization Models (Optimization models are all deterministic and macroscipic): SOAP (Most Signal Operations Analysis Package recent one is part  Design the signal timing for any three- or four- legged of HCS2000) intersection  Find optimum cycle length & splits  A deterministic, macroscopic, analytical optimization model PASSER-V Progression Analysis and Signal System Evaluation Routine by Texas (consisting of PASSER-II for arterials and PASSER-III for Transportation diamond interchanges using a single traffic controller, GA-based Institute timing optimization)  Analyze individual signalized intersection progression along an arterial street with varied multi-phase sequences  Calculate phase intervals, offsets, and demand/capacity ratios to evaluate the level of service at each intersection  A deterministic, macroscopic optimization model based on green band approach to signal timing AAP Arterial Analysis Package  This is like a shell program, integrating SOAP, PASSER-II and TRANSYT-7F (but you have to buy TRANSYT-7F separately) Synchro Signal synchronization? By  Model and optimize traffic signal timings (Optimize cycle Trafficware lengths and splits)  Fully interactive (no other interactive software needed for input data preparation – one reason why this one became so popular among practitioners)  Determine capacity (using HCM)  When a signal is coordinated with others, Synchro explicitly calculates the platoon factor MAXBAND Maximum Bandwidth  Optimize signal offsets to maximize green bandwidth along signalized arterials  A deterministic, macroscopic optimization model TRANSTY-7F Traffic Network Study Tool 8th Version By  Develop signal timing plans for arterial and grid networks University of  Minimize stops and delays for the system as a whole rather Florida than maximizing the arterial bandwidth  A deterministic, macroscopic optimization model using a platoon dispersion model of traffic in conjunction with a "hill-climbing" optimization model Simulation Models (Simulation models are all microscopic and stochastic):

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TEXAS By Texas Transportation Institute TSIS

WATSim By KLD Associates

SimTraffic by Trafficware


Traffic Experimental Analytical Simulation  A microscopic, stochastic simulation model for single intersections  Can be used for designing (a) intersection geometry, (b) traffic control options for four way stops, two-way yield signs and no control, and (c) signal control options Traffic Software Integrated System  A microscopic, stochastic simulation model for freeways and surface streets combined  Simulate traffic along a corridor by a simulation software called CORSIM, consisting of NETSIM (Network Simulation) and FRESIM (Freeway Simulation) software Wide Area Traffic Simulation  A microscopic, stochastic simulation model for freeways and surface streets combined  Surface streets and freeways are integrated. (note that both NETSIM and FRESIM were originally developed by KLD) Simulation of traffic?  A microscopic, stochastic simulation model for a network of signalized and unsignalized intersections  This is a companion software to Synchro

Transims By Los Alamos National Laboratory

The TRansportation ANalysis SIMulation System (TRANSIMS) is a set of new transportation and air quality analysis and forecasting procedures developed to meet the Clean Air Act, the Intermodal Surface Transportation Efficiency Act, Transportation Equity Act for the 21st Century, and other regulations.

Dynasmart By University of Texas Austin (H. Mahmassani)

DYNASMART-X is a state-of-the-art real-time Traffic Estimation and Prediction System (TrEPS) for effective support of Advanced Traffic Management Systems (ATMS) and Advanced Traveler Information Systems (ATIS). DYNASMART-P is a state-of-the-art dynamic network analysis and evaluation tool.

UrbanSim By University of Washington (Paul Waddell) VISSIM/VISUM

UrbanSim is a software-based simulation model for integrated planning and analysis of urban development, incorporating the interactions between land use, transportation, and public policy. It is intended for use by Metropolitan Planning Organizations and others needing to interface existing travel models with new land use forecasting and analysis capabilities. Simulation software from Germany/Planning software

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Simulation software from Spain (traffic and planning combined)


Simulation software from UK


A companion to TransCAD (Planning software)

Issues of Traffic Simulation No. of replications

Length of run

A rule of thumb = 3 replications are the minimum. But 10 replications are recommended (if you want to do any statistical analysis, such as paired t-test A typical run length = 15 min. But this depends on the situation you are dealing with. If % of occurrence of an event of interest is very low, then you need to run longer. Know what's modeled by the software (This applies to optimization models, also.) Read the manual carefully.

Detail of specific detailed mechanisms Avoiding using the model beyond its limits Selecting performance Read the definitions of MOE terms carefully. measures for the model User-friendly input Seeing is believing. It is amazing and getting easier to and output prepare input data to complex simulation models.

Representation of the Network 

Most simulation software uses a link-node representation of a study network (like Synchri and CORSIM). VISSIM has a link and connector representation of a study network.

Each software has its own rule for naming the links and nodes. You need three types of nodes. 1. 2. 3. 4.

Source or sink node (Vehicles enter or exit the study network) Dummy node (Dummy nodes usually have 100% green time) Actual node for analysis (Intersections under study) Links (each direction gets one link assigned)

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Without dummy nodes, you cannot properly simulate traffic on approach links. 

Most simulation software requires the following data

Geometric input data Traffic input data Control input data

Describes the physical network over which the vehicles travel Describes the number and type of vehicles moving on the network Describes type of traffic control and its parameters