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|Federal Highway Administration > Publications > Public Roads > Vol. 68 · No. 5 > Traffic Analysis Toolbox|
Publication Number: FHWA-HRT-05-004
Traffic Analysis Toolbox
by James P. McCarthy
FHWA releases new guidelines to help analysts improve modeling to reduce congestion and improve safety.
The Nation's roadways have become so overloaded with traffic that they can have an adverse affect on the quality of life for many Americans. According to the Texas Transportation Institute's 2004 Urban Mobility Report, the annual delay per rush hour traveler has grown from 16 hours to 46 hours since 1982, and the annual financial cost of traffic congestion has ballooned to more than $63 billion (expressed in 2002 dollars). Congestion on urban freeways and arterials continues to increase at an alarming rate, the report says, increasing the potential for crashes and long delays, releasing harmful air pollutant emissions, and increasing operating costs.
In past decades, numerous models were developed to simulate traffic flow, evaluate operations and road safety, and optimize control systems. "The tools have become much more useable through better software development in the last 5 years," says John Hourdakis, a research fellow at the University of Minnesota, "and we now have data being collected and archived in new intelligent transportation system applications for analysis."
Despite the widespread use of traffic simulation software, however, opinions on how and which simulation procedures should be used vary among practitioners, making it difficult to replicate and share results. In December 2001, FHWA organized a team of engineers to evaluate many of these new software programs and provide guidance on how to use them effectively. The fruits of their labors culminated in a multivolume Traffic Analysis Toolbox. With the first three volumes already available online, and the remaining volumes due in early 2005, FHWA is providing the leadership and training to help traffic managers use these tools and concepts to improve the Nation's highway system.
Defining the Problem
Through changes in the Federal-Aid Highway Program in the Intermodal Surface Transportation Efficiency Act (ISTEA) and the Transportation Equity Act for the 21st Century (TEA-21), the scope and design of improvements to existing facilities no longer follow a predetermined nationwide plan. Project size and specifications, such as lane configurations, interchange forms, and control strategies, now are based more on current operational problems, projected future congestion, and safety concerns than on a predetermined design. In most cases, funds are limited and the best possible use of available dollars may require more thorough analyses. When setting priorities and selecting projects or operational strategies, a more rigorous traffic study, conducted by a knowledgeable engineering staff, becomes imperative.
In the postinterstate era, the challenge for transportation agencies is to implement capital and operational improvements that have meaningful impacts on congestion and safety. "The ability to make informed decisions as to how to address these challenges is much more difficult than it has been in the past," says Rick Arnebeck, area manager with the Minnesota Department of Transportation (Mn/DOT). "Fixing congestion and safety problems can be very complicated. Projects now are much more complicated in urban and suburban areas with many competing demands and a variety of parochial views. A reliable and accurate traffic analysis can be crucial to reaching agreement when deciding which improvements to advance among a larger body of stakeholders."
One construction project in Florida, known as the I–4 "Trans4mation" project, reflects the new demand for a more rigorous analysis of project scoping and staging in congested corridors. Complicated system interchanges and the demand for high-volume local access required planners to conduct a thorough study using the full range of analysis tools to bring together a coherent improvement program. The I–4 project used travel demand models, highway capacity analysis, and traffic simulation to develop a new vision for the heavily congested I–4 corridor.
"The I–4 system access modification challenged us to think beyond the interstate and the traditional highway capacity analysis," says Grant Zammit with the FHWA Resource Center in Atlanta, GA. "We had to consider the implications of geometric and operational strategies in tandem, understand the implications of our decisions on the entire transportation network, and formulate a concept that addressed an array of requirements and measures. We must accept the challenge to further define what questions the traffic analysis will address; craft the scope, methodology, and output that provide us with information; and package this into intelligence that the decisionmaker would not have otherwise."
Assembling a Team
In response to the growing need for effective traffic analyses, a group of FHWA traffic engineers formed a grassroots team to take on the challenge. The group includes engineers from the division offices, resource centers, the Turner-Fairbank Highway Research Center (TFHRC), and the Office of Operations at FHWA headquarters.
The FHWA traffic analysis team met in December 2001 to lay out a plan to meet the challenge of improving traffic analyses to meet the needs of the Federal-aid program. Today, the plan is being implemented with support from the Office of Operations.
The team's goals are to elevate the awareness and effective use of traffic analysis tools, develop and market guidelines for traffic analysis applications, provide training and technical assistance on selected tools, and provide outreach and information exchange with professional organizations.
The team spearheaded the development of a series of technical documents, known as the Traffic Analysis Toolbox, as well as training efforts to help traffic managers use available engineering tools most effectively to improve their project designs.
Overview of Traffic Analysis Tools
Released in June 2004 and available online, Traffic Analysis Toolbox Volume I: Traffic Analysis Tools Primer (FHWA-HRT-04-038) provides a user-friendly, high-level overview of the types of analysis tools that transportation practitioners can use to model traffic flow. "The primer fills the need for a clear and useful explanation of the tools available for transportation engineers and managers to use in project development," says FHWA's Zammit. "The document provides guidance and advice on the appropriateness of applying various analysis methods to the complete spectrum of traffic and safety problems."
A section on the role and value of traffic analysis tools, for example, explains how models can help practitioners improve the decisionmaking process by estimating the impact of deploying various strategies, helping set priorities among competing projects, and providing a consistent approach for comparing potential improvements or alternatives. Traffic analysis tools can help managers improve the productivity of design and evaluation time and reduce expenses because the tools tend to be less costly when compared to pilot studies, field experiments, or full implementation costs. In addition, some tools have excellent graphical and animation displays that can enhance the impact of marketing presentations to the public and stakeholders.
Another section describes the challenges and limitations of using traffic analysis tools. Each tool is designed to perform different functions, and no one analytical tool can solve every problem. Therefore, the primer recommends that managers consider a number of factors when selecting an appropriate tool, including availability of quality data; long computer run times, which may range from a few seconds to several hours; and the availability of funding for conducting the study, purchasing tools, running analytical scenarios, and training the users.
The primer document targets engineers and managers who may not have been trained in or practiced as traffic engineers but nonetheless rely on these engineers to develop new projects. "The vast majority of project managers come from fields other than traffic engineering," says Zammit, "so they have limited knowledge of the tools used in the practice. With this primer, they will be better prepared to address the traffic engineering aspects of project development and design."
Overall, the concise Traffic Analysis Tools Primer will assist transportation engineers as they review projects and provide guidance to their State and local partners. The document also will be useful to managers at State DOTs as they develop the scope of work and schedules, and manage their projects.
Providing guidance on selecting the appropriate analysis tool for the job is the focus of the second installment: Traffic Analysis Toolbox Volume II: Decision Support Methodology for Selecting Traffic Analysis Tools (FHWA-HRT-04-039).
Published online in July 2004, Volume II builds on the principles and advice in the primer, providing traffic engineers and operations professionals with a process for selecting the most effective traffic analysis tool for planning design and operational improvements. The process defined in the document helps engineers choose from various categories of traffic analysis tool, such as traffic simulation, travel demand, signal optimization, or analytical/deterministic tools (based on procedures in the Highway Capacity Manual).
The guide established a set of criteria for selecting the appropriate type of tool, and each tool category is scored according to its relevance to those criteria. Among the criteria are the analysis context, study area, facility type, travel mode, management strategy, traveler response, performance measures, and cost effectiveness.
Volume II also features worksheets for an analyst to rate a tool category for a particular transportation analysis task. Although the team originally created the guide as a written document, during the development process, the members recommended the addition of an interactive process to apply the selection methodology. Currently only a static version of the guide is available.
The third report, Traffic Analysis Toolbox Volume III: Guidelines for Applying Traffic Microsimulation Modeling Software (FHWA-HRT-04-040), provides a recommended process for using traffic simulation software in transportation analyses.
Microsimulation is the modeling of individual vehicle movements on a second or subsecond basis for the purpose of assessing the traffic performance of highway and street systems, transit, and pedestrians. According to FHWA staff working on the project, Volume III was a large undertaking for the team because a well-documented or accepted application methodology did not exist. For the first time, this report provides traffic engineering practitioners with a thorough and clear guide on applying microsimulation models to traffic analysis problems. The report also emphasizes how the microsimulation process relates to the overall design process and the development and review of alternative solutions.
Also released in July 2004, Volume III will aid traffic managers in applying microsimulation models consistently and reproducibly, and will further support the credibility of traffic analysis reports prepared in the design of large and complex urban projects. The guidelines provide the reader with a seven-step process that begins with project scope and ends with the final project report. The process is generic in that it is independent of the specific software tool used in the analysis. In fact, the first step in the process involves picking the appropriate tool for the job.
"By defining the simulation in an easy-to-understand format, we removed some of the mystery from the process," says Jaimie Sloboden, traffic engineer with Short Elliott Hendrickson Inc. "This document is meant to be the industry standard for the application of microsimulation. With the process more clearly defined, traffic engineers will have an easier time using simulation software and producing results that will positively impact the design process."
During the design of a freeway reconstruction project on I–494 in Minneapolis, MN, for example, traffic engineers effectively used microsimulation to evaluate possible reconfiguration options for a 40-year-old, substandard cloverleaf interchange. The simulation study presented the positive and negative impacts of multiple options in a succinct graphical format, enabling the transportation agencies to approve a final layout.
The intended audience for the microsimulation report includes simulation analysts and reviewers, as well as those who procure simulation services.
Minnesota's CORSIM Manual
Agencies that have used the Volume III document, even in its draft form, already have made dramatic improvements in the practice of traffic simulation. For example, through a partnership between the FHWA Minnesota Division, Mn/DOT, and Hennepin County, MN, developers recently completed the first example of a customized, product-specific guide for CORSIM (short for "corridor simulation").
CORSIM is a comprehensive simulation program that models traffic and traffic control systems using commonly accepted models for vehicle and driver behavior. The program applies to surface streets, freeways, and integrated networks, and has the ability to model systems featuring the complete selection of control devices, including stop and yield signs, traffic signals, and ramp metering.
A new guide, the Advanced CORSIM Training Manual, represents Mn/DOT's standard procedure for all engineering consultants to use when preparing traffic simulation studies for State and locally funded projects. The manual serves several important purposes:
"Many of the practitioners who were using CORSIM had good ideas on the application but were developing and using models that could not be readily reviewed, understood, accepted, or shared by others," says Linda Taylor, traffic engineer with Mn/DOT. "The methodology laid out in the Advanced CORSIM Training Manual has been a cornerstone in the application and acceptance of microsimulation in Minnesota. CORSIM models built and used for projects are now shared and reused on adjacent and/or subsequent projects in the Twin Cities metropolitan area because the manual standardized the methods and computer coding of the network, much in the way the CAD [computer-aided design] process was standardized and streamlined 15 years ago. The methodology also has significantly decreased review times and improved the performance of traffic engineers."
Although the document was developed for local use, because it was built upon the FHWA microsimulation process, the manual can be readily transformed and reused by other FHWA divisions and State DOTs. To download the manual, visit www.dot.state.mn.us/trafficeng/modeling/index.html.
Coming Soon: Volumes IV and V
By early 2005, FHWA will add two more documents to the Traffic Analysis Toolbox: Volume IV: CORSIM Application Guidelines and Volume V: Traffic Analysis Tools Case Studies and Best Practices.
The CORSIM Application Guidelines will assist engineers using the software to develop and test various geometric network configurations and traffic volume scenarios for roadways. The document will build upon the more generic simulation guidelines presented in Volume III, offering a more specific set of guidelines developed particularly for using CORSIM. The CORSIM Application Guidelines use the seven-step process defined in Volume III and provide more specific application instructions from CORSIM practitioners. In particular, the document will provide a wealth of detailed information on constructing high-quality CORSIM networks and an efficient process for calibrating and documenting results.
The case studies and best practices highlighted in the Volume V report will help transportation managers gain a broader awareness of what they can accomplish using simulation software, how they can save time and resources, and how they can produce more defensible results that will feed into problem solving and decisionmaking. Similarly, transportation engineers and analysts will gain insights into selecting an appropriate application and how to assess and interpolate analysis results. One case study, for example, analyzed how a proposed busway and various transit alternatives might improve the person carrying capacity on K Street in Washington, DC.
"With these new documents, area engineers, project managers, and consultants are now better equipped to make decisions on how to use traffic engineering tools in their day-to-day operations," says Acting Division Administrator Robin Schroeder of the FHWA Minnesota Division.
The goal is to apply all of these documents to planning and designing infrastructure improvements and operational changes that will reduce congestion and enhance safety on U.S. highways well into the future.
James P. McCarthy, P.E., P.T.O.E. is a traffic operations engineer with FHWA in St. Paul, MN. He works with traffic analysis, traffic operations, and ITS deployment. He currently is working on ITS operational tests, new traffic operation centers, deployment of roadside devices, and creation of advance traveler information systems. McCarthy is a member of the FHWA Traffic Analysis Team, which supports the CORSIM program and the development of new tools and guidance for the useof microsimulation. He holds a bachelor's of science and master's in civil engineering from the University of Minnesota. He is a licensed professional engineer in Minnesota and earned the title professional traffic operation engineer from the Institute of Transportation Engineers.
To access the Traffic Analysis Toolbox online, visit http://ops.fhwa.dot.gov/Travel/Traffic_Analysis_Tools/traffic_analysis_toolbox.htm. For more information, contact James P. McCarthy at 651–291–6112, firstname.lastname@example.org.
Special thanks to Linda Taylor of Mn/DOT Metro District and Jamieson Sloboden of Short Elliott Hendrickson Inc. for their work in producing the Advanced CORSIM Training Manual.
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