Introduction

Traffic microsimulation software has become increasingly popular as a traffic analysis tool used in transportation analyses.  One reason for this increase is the need to model and analyze the operation of complex transportation systems under congested conditions.  Much of the current transportation investment program is trying to improve traffic operations on congested freeways and arterials and microsimulation is becoming the analysis tool of choice to understand and evaluate improvements.  Where some analytical techniques break down under these types of conditions, microsimulation has the potential to successfully model these complex scenarios.  Another reason for the increase in popularity of microsimulation is the increased availability of personal computers capable of performing a large number of calculations very quickly.  However, despite the widespread use of traffic microsimulation software, there are a variety of conflicting thoughts and practices on when microsimulation should be used and how it should be applied.  This document is designed to provide guidelines on how to consistently use the CORridor SIMulation (CORSIM) simulation model to perform a traffic analysis, and it was developed in consultation with the software developer.

Overview of FHWA Traffic Analysis Toolbox

Traffic Analysis Tools is a collective term used to describe a variety of software-based analytical procedures and methodologies that support different aspects of traffic and transportation analyses.  Traffic analysis tools include methodologies such as sketch-planning, travel demand modeling, traffic signal optimization, and traffic simulation.  The purpose of the FHWA Traffic Analysis Toolbox is to provide guidance, recommendations, and examples on the selection and use of traffic analysis tools.  The volumes in the toolbox are described below.

• Volume I: Traffic Analysis Tools Primer.  The purpose of this volume is to give the reader an overview of the different types of traffic analysis tools and to describe their role in transportation analyses.

• Volume II: Decision Support Methodology for Selecting Traffic Analysis Tools.  The purpose of this volume is to provide an overview of the role of traffic analysis tools in transportation studies and to present a detailed methodology for selecting the appropriate tool for the current analysis.

• Volume III: Guidelines for Applying Traffic Microsimulation Modeling Software.  The purpose of this volume is to provide a recommended process for using traffic microsimulation software in transportation analyses.  Volume III is generic, in that it is independent of the specific software tool used in the analysis.

• Volume IV: Guidelines for Applying CORSIM Microsimulation Modeling Software (this document).  The purpose of this volume is to provide a recommended process for using CORSIM traffic simulation software in transportation analysis.  These guidelines follow the process outlined in Volume III using CORSIM as the microsimulation tool.

• Volume V: Traffic Analysis Tools Case Studies.  The purpose of this volume is to provide real-world examples of the application of traffic analysis tools to show what can be achieved when the analysis methods described in the Traffic Analysis Toolbox are correctly applied.  Altogether, these case studies show how different types of tools have been effectively applied to the wide range of problems that confront every community and agency.

These volumes can be downloaded at the FHWA Traffic Analysis Tools web site at: http://ops.fhwa.dot.gov/trafficanalysistools/index.htm

Purpose and Objectives of this Document

CORSIM is the core simulation and modeling component of the Traffic Software Integrated System (TSIS) tool suite.  The guidelines herein provide the reader with a seven-step process that begins with project scope and ends with the final project report.  Volume IV is specific to using CORSIM and TSIS and is based on TSIS/CORSIM Version 6.0, released in 2006.  The purpose of this document is to assist the transportation community in creating an appropriate, consistent, and repeatable process for applying CORSIM traffic simulation software to transportation project analyses.

This document is to be used in conjunction with the other volumes in the FHWA Traffic Analysis Toolbox.  CORSIM and its user environment, TSIS, should not be used unless justified by the analysis outlined in Volumes I and II.

Specific objectives of this document are to explain and provide guidance on:

• How to define and scope a CORSIM analysis.
• What data to collect, and when and how to collect the data.
• How to consistently build a CORSIM network.
• How to calibrate a CORSIM model.
• How to conduct an alternative analysis in CORSIM.
• What and how to report the results of a CORSIM analysis.
• How to apply the strengths and overcome the weaknesses of CORSIM.

This document is not intended to explain the mechanics of how to code each parameter in CORSIM; rather, the intention is to explain to a user who already understands the basics of CORSIM how to apply CORSIM to a transportation analysis in an appropriate, consistent, and repeatable process.

Target Audience for this Document

This document is a resource guide targeted at practitioners, managers, and researchers involved in the transportation analysis process.  Each of these target audiences has a different role to play in the analysis process so the use and application of this document will differ between each of these audiences.  The following discussion demonstrates how these target audiences could use this document.

Practitioners/analysts:  In most instances, practitioners will not need to read the entire document at the start of each new traffic analysis, but can simply refer to those sections containing information relevant to their assignments.  Chapter 1 should be reviewed so that analysts understand their role in the development of the project scope and how their analysis affects the overall project objectives.  Chapters 2 through 5 should be used as a reference guide and consulted as needed when developing the model.  Chapter 5 is particularly important and may offer some crucial guidance on how the model should be calibrated to represent real-world conditions.  Chapters 6 and 7 should be reviewed by practitioners to obtain guidance on interpretation and presentation of results and on preparing the final documentation for the project.  The Appendices can be a great advantage to the practitioner providing a wealth of information that should be consulted as needed.

Decision makers/managers:  Decision makers will find this document useful in understanding the overall microsimulation process.  A review of the Introduction will provide a high-level understanding of CORSIM and the other tools in the Traffic Analysis Toolbox.  Chapter 1 will be useful to decision makers in obtaining an understanding of the project scoping process.  Decision makers and managers should use Chapter 1 to ensure the project scope are adequately developed and agreed upon by all parties involved in the analysis and review process before commencing the project analysis.  Chapters 6 should be reviewed for guidance on the management of the alternatives and the interpretation of results and recommendations.   Finally, Chapter 7 should be consulted for guidance on the documentation required to present the material in a manner that provides sufficient detail to aid in the decision making process.

Researchers: Researchers will find the material beneficial for providing overview information in areas such as Run-Time Extensions, documentation of CORSIM theory and logic using TSIS/CORSIM to perform a sensitivity study, or any attempts at novel or complex applications.   Chapters 2 through 6 should be used as a reference guide and consulted as needed when developing a CORSIM model.  The appendices will also be of great benefit to researchers because of the detail provided on CORSIM theory and complex applications that will benefit the more advanced user.

By making use of this document, it is envisioned that the reader will gain insight into enhancing the reliability and credibility for future traffic analysis.  Table 1 provides a quick reference to the chapters that would be most applicable for each staff category.  Then the remainder of the document can be used as a resource guide, which can be consulted as needed.

Table 1 . Professional staff and suggested chapters.

CORSIM Overview

CORSIM has a long history reaching back to the 1970’s and mainframe computers.  Many fixes, improvements, and enhancements have been made since the original coding but the basic theory of CORSIM still retains its roots.  In 1994, two separate software programs, one for modeling surface streets (NETSIM) and one for modeling freeways (FRESIM), were combined to form the CORSIM program.  In a corridor simulation with both surface streets and freeways, each type of facility is referred to as a subnetwork.⁽¹⁾

CORSIM applies time step simulation to model traffic operations.  CORSIM is a microscopic simulation model, implying that it models individual vehicle movements based on car-following and lane-changing theories on a second-by-second basis for the purpose of assessing the traffic performance of highway and street systems.

CORSIM is a stochastic simulation model, which means that it incorporates random processes to model complex driver, vehicle, and traffic system behaviors and interactions.  Stochastic simulation models produce output that is itself random.  Because the output of a stochastic model is random, each run of a stochastic simulation model produces only estimates of a model’s true characteristics for a particular set of input parameters.  Thus, relying on the measures of effectiveness (MOEs) generated from a single run of CORSIM may be misleading.  To produce meaningful MOEs, several independent runs of the model will be required for each set of input parameters to be studied.  A more in-depth discussion of CORSIM theory is provided in Appendix A.

CORSIM Model Development and Application Process

Ideally, two studies with the same inputs and implemented by different analysts should produce nearly identical conclusions.  However, this is not often the case because analysts have varying levels of experience and use different approaches for applying a model (i.e., they may calibrate the model differently).  This document presents a consistent and comprehensive process for applying TSIS/CORSIM to a traffic analysis study so that the analysis can be consistent, traceable, and repeatable.  By using the process outlined in this document, future modelers will benefit from the past experiences of others.

The overall process for developing and applying a TSIS/CORSIM model to a specific traffic analysis problem consists of seven major tasks.  A flow chart capturing this overall process is presented in Figure 1.  The process as described here may be useful for a procurer in composing a Scope of Work before beginning a microsimulation analysis.  Each task is described in more detail in subsequent chapters.

 

Figure 1 . Flowchart.  CORSIM model development and application process.

Organization of this Document

This document is organized into the following chapters and appendices:

Introduction (this chapter) highlights the key guiding principles of CORSIM and provides an overview of this document.

• Chapter 1 addresses the management, scope, and organization of CORSIM analyses.
• Chapter 2 discusses the steps necessary to collect, prepare, and calibrate input data for use in CORSIM models.
• Chapter 3 discusses the coding of input data into the CORSIM models.
• Chapter 4 presents methods for error-checking the CORSIM models.
• Chapter 5 provides guidance on the calibration of CORSIM models to study area traffic conditions.
• Chapter 6 explains how to use CORSIM models for alternatives analysis.
• Chapter 7 provides guidance on the documentation of CORSIM model analysis.
• Appendix A provides an introduction to the fundamentals of CORSIM model theory.
• Appendix B provides an overview of CORISM capabilities and limitations.
• Appendix C provides guidance on the initialization period.
• Appendix D provides guidance on the generation and usage of random numbers in CORSIM.
• Appendix E provides guidance on the vehicle entry headway generation in CORSIM.
• Appendix F provides a discussion of actuated signal control in CORSIM.
• Appendix G provides a coded input data checklist to be used during the error checking process.
• Appendix H provides guidance on understanding CORSIM output.
• Appendix I answers Frequently Asked Questions about CORSIM and other TSIS tools.
• Appendix J provides guidance on converting between systems of actuated control parameters.
• Appendix K provides guidance on coding techniques for complex situations.
• Appendix L provides guidance on the run-time extension.
• Appendix M provides guidance on the CORSIM path-following capability.
• Appendix N provides guidance on the CORSIM emergency vehicle capability.
• Appendix O provides guidance on CORSIM file name conventions (i.e., file extensions).