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TFHRC Home > Safety > Safety Publications > 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.
FHWA-HRT-07-045, June 2007
PDF Version (626.73 kb)
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
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.
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.
1. Report No. FHWA-HRT-07-045 |
2. Government Accession No. |
3. Recipient's Catalog No. |
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4. Title and Subtitle Interchange Safety Analysis Tool (ISAT): User Manual |
5. Report Date June 2007 |
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6. Performing Organization Code: 440545878 |
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7. Author(s) D.J. Torbic, D.W. Harwood, D.K. Gilmore, and K.R. Richard |
8. Performing Organization Report No. 110448 |
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9. Performing Organization Name and Address Midwest Research Institute |
10. Work Unit No. 001 |
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11. Contract or Grant No. DTFH61-05-P-00302 |
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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 |
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14. Sponsoring Agency Code HRDS-05 |
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15. Supplementary Notes FHWA Contracting Officer's Technical Representative (COTR): Joe G. Bared, HRDS-05 |
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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. |
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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. |
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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 |
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
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 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 49. Number of predicted crashes for individual crossroad ramp terminals and intersections
Table 51. Number of predicted crashes for Individual arterial crossroad roadway segments
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