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Publication Number: FHWA-HRT-07-045
Date: June 2007

Applications of ISAT, Interchange Safety Analysis Tool (ISAT): User Manual

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The Interchange Safety Analysis Tool that accompanies this user manual is available in an Excel spreadsheet format. Please contact Wei Zhang at wei.zhang@dot.gov, or Joe Bared at joe.bared@dot.gov for the software.

Foreword

This User Manual describes the usage and operation of the spreadsheet-based Interchange Safety Analysis Tool (ISAT). ISAT provides design and safety engineers with an automated tool for assessing the safety effects of geometric design and traffic control features at an existing interchange and adjacent roadway network. ISAT can also be used to predict the safety performance of design alternatives for new interchanges and prior to reconstruction of existing interchanges. The primary outputs from an analysis include: the number of predicted crashes for the entire interchange area, the number of predicted crashes by interchange element type, the number of predicted crashes by year, and the number of predicted crashes by collision type. The User Manual presents basic information for getting started with using ISAT, the general methodology that users will follow when conducting an analysis with ISAT, input requirements of the program, default data incorporated within the program and recommendations on when and how these default data should be updated by the user, output reports generated by ISAT, and general information on different applications for which ISAT can be applied. For more information on ISAT, the user is referred to the final project report for Contract No. DTFH61-05-P-00302.

Michael Trentacoste

Director, Office of Safety

Research and Development

Notice

This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this document.

The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers' names appear in this report only because they are considered essential to the objective of the document.

Quality Assurance Statement

The Federal Highway Administration (FHWA) provides high-quality information to serve Government, industry, and the public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its information. FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality improvement.

Technical Report Documentation Page

1. Report No.

FHWA-HRT-07-045

2. Government Accession No.

3. Recipient's Catalog No.

4. Title and Subtitle

Interchange Safety Analysis Tool (ISAT): User Manual

5. Report Date

June 2007

6. Performing Organization Code:

440545878

7. Author(s)

D.J. Torbic, D.W. Harwood, D.K. Gilmore, and

K.R. Richard

8. Performing Organization Report No.

110448

9. Performing Organization Name and Address

Midwest Research Institute
425 Volker Boulevard
Kansas City, MO 64110

10. Work Unit No.

001

11. Contract or Grant No.

DTFH61-05-P-00302

12. Sponsoring Agency Name and Address

Federal Highway Administration

Turner-Fairbank Highway Research Center

Office of Safety Research & Development

6300 Georgetown Pike

McLean, VA 22101-2296

13. Type of Report and Period Covered

User Manual 9/7/2005-6/31/2007

14. Sponsoring Agency Code

HRDS-05

15. Supplementary Notes

FHWA Contracting Officer's Technical Representative (COTR): Joe G. Bared, HRDS-05

16. Abstract

This User Manual describes the usage and operation of the spreadsheet-based Interchange Safety Analysis Tool (ISAT). ISAT provides design and safety engineers with an automated tool for assessing the safety effects of geometric design and traffic control features at an existing interchange and adjacent roadway network. ISAT can also be used to predict the safety performance of design alternatives for new interchanges and prior to reconstruction of existing interchanges. The primary outputs from an analysis include: the number of predicted crashes for the entire interchange area, the number of predicted crashes by interchange element type (i.e., mainline freeway segments, ramps, ramp terminals and intersections, and crossroad roadway segments), the number of predicted crashes by year, and the number of predicted crashes by collision type.

This User Manual presents basic information for getting started with using ISAT, the general methodology that users will follow when conducting an analysis with ISAT, input requirements of the program, default data incorporated within the program and recommendations on when and how these default data should be updated by the user, output reports generated by ISAT, and general information on different applications for which ISAT can be applied. An example problem is also provided on the safety performance of a rural diamond interchange and surrounding roadway network, illustrating user inputs and generated output reports.

17. Key Words

Interchange, safety, geometric design, safety performance function

18. Distribution Statement

No restrictions. This document is available through the National Technical Information Service, Springfield, VA 22161.

19. Security Classif. (of this report)

Unclassified

20. Security Classif. (of this page)

Unclassified

21. No. of Pages

105

22. Price

Form DOT F 1700.7 (8-72)

Reproduction of completed page authorized

SI (Modern Metric) Conversion Factors

Table of Contents

List of Figures

Figure 1. Example interchange illustrating individual components

Figure 2. General interchange input data screen

Figure 3. Typical gore area characteristics

Figure 4. Typical ramp configurations

Figure 5. Sample application of ISAT to a full diamond interchange

Figure 6. Sample application of ISAT to a partial cloverleaf interchange

Figure 7. Sample application of ISAT to a full cloverleaf interchange

Figure 8. Sample application of ISAT to a directional interchange

List of Tables

Table 1. Summary of input variables for general interchange area

Table 2. Example data for rural diamond interchange (Input-General)

Table 3. Mainline freeway segments input data screen

Table 4. Summary of input variables for mainline freeway segments

Table 5. Example data for rural diamond interchange (Input Mainline Freeways)

Table 6. Ramps input data screen

Table 7. Summary of input variables for ramps

Table 8. Example data for rural diamond interchange (Input Ramps)

Table 9. Crossroad ramp terminal and intersection input data screen

Table 10. Summary of input variables for crossroad ramp terminals and intersections

Table 11. Example data for rural diamond interchange (Input Ramp Terminals)

Table 12. Arterial crossroad roadway segment input data screen

Table 13. Summary of input variables for crossroad roadway segments

Table 14. Example data for rural diamond interchange (Input Crossroad Segments)

Table 15. SPF Coefficients and parameters for mainline freeway segments

Table 16. Definitions of coefficients and parameters of SPFs for mainline freeway segments

Table 17. SPF Coefficients and parameters for ramps

Table 18. Definitions of coefficients and parameters of SPFs for ramps

Table 19. SPF Coefficients and parameters for acceleration lanes

Table 20. Definitions of coefficients and parameters of SPFs for acceleration Lanes

Table 21. SPF Coefficients and parameters for crossroad ramp terminals and intersections

Table 22. Definitions of coefficients and parameters of SPFs for crossroad ramp terminals and intersections

Table 23. SPF coefficients and parameters for crossroad segments

Table 24. Definitions of coefficients and parameters of SPFs for crossroad segments

Table 25. Calibration coefficients for mainline freeway segment SPFs

Table 26. Calibration coefficients for ramp SPFs

Table 27. Calibration coefficients for crossroad ramp terminal and intersection SPFs

Table 28. Calibration coefficients for crossroad segment SPFs

Table 29. Nomenclature for calibration procedures

Table 30. Example data for calibration procedure (Input-General)

Table 31. Example data for calibration procedure (Input Mainline Freeways)

Table 32. Example output report for calibration procedure

Table 33. Example calibration procedure (Input Calibration Worksheet)

Table 34. Nomenclature for crash distribution calculations

Table 35. Proportions of crashes by severity and type for mainline freeways

Table 36. Proportions of crashes by severity and type for ramps

Table 37. Proportions of crashes by severity and type for crossroad ramp terminals and intersections

Table 38. Proportions of crashes by severity and type for arterial crossroad roadway segments

Table 39. General interchange information (General Output Report)

Table 40. Number of predicted crashes for entire interchange area (General Output Report)

Table 41. Number of predicted crashes by interchange element type (General Output Report)

Table 42. Number of predicted crashes by year (General Output Report)

Table 43. Number of predicted crashes by collision type (General Output Report)

Table 44. Number of predicted crashes by collision type for all mainline freeway segments combined

Table 45. Number of predicted crashes for individual mainline freeway segments

Table 46. Number of predicted crashes by collision type for all ramps combined

Table 47. Number of predicted crashes for individual ramps

Table 48. Number of predicted crashes by collision type for all crossroad ramp terminals and intersections combined

Table 49. Number of predicted crashes for individual crossroad ramp terminals and intersections

Table 50. Number of predicted crashes by collision type for all arterial crossroad roadway segments combined

Table 51. Number of predicted crashes for Individual arterial crossroad roadway segments

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