U.S. Department of Transportation
Federal Highway Administration
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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
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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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This section provides general information on using and navigating through the ISAT software. The following issues are discussed:
Because ISAT is an Excel spreadsheet workbook, system requirements for the ISAT software are essentially the same as those for the Microsoft Office Suite; please consult installation requirements for these products for more detailed information. Further, approximately 765 kilobytes (KB) of memory are needed for this program before data entry. Adding an interchange to the database, including consideration of all elements for that interchange, requires approximately 3.2 megabytes (MB) of additional storage. The required storage increases with the number of elements and sites entered for an interchange.
Installation of ISAT Software
The following procedure should be used to install the ISAT software on a computer from a CD-ROM:
Microsoft Excel Spreadsheet Software Basics
ISAT is an Excel workbook program that operates within Microsoft Windows operating system environments: Windows 95, Windows NT 4.0, or later versions of Windows. ISAT has been developed for Excel 2003 spreadsheet software or later versions of Microsoft Excel spreadsheet software. The Installation of ISAT Software section of this manual provides instructions for installation of ISAT on a personal computer. Like many Microsoft applications, Excel spreadsheet software is easily started in various ways. From the Start button located on the task bar at the bottom of the screen, click on the Programs option and then on Microsoft Excel. Click once with the left mouse button, and in a few moments the Excel screen appears. There may also be an icon on the desktop or on a toolbar that can be clicked to start Excel. ISAT can also be started from Microsoft Windows Explorer by browsing to find ISAT's file location and double-clicking its icon.
Open ISAT from its file location by using the Open option in the File menu. Like most Windows programs, Excel provides a host of ways to control program operations. The mouse, keyboard, menus, dialog boxes, command buttons, key combinations, and more can be used. With ISAT, there are two types of navigation: among worksheets and among cells in a worksheet.
Navigation among worksheets is accomplished by clicking the worksheet tabs at the bottom of the workbook window. Within ISAT, navigation between worksheets can also be accomplished by using hyperlinks embedded in the program. Hyperlinks are colored, underlined text elements that jump to a location in the workbook when clicked. The titles of all hyperlinks describe the type of information contained on the respective worksheet that will appear upon clicking the hyperlink, with the exception of those labeled "Home." These hyperlinks return users to the Input-General worksheet in the workbook.
The Tab key and Enter key provide the primary method of navigating through the columns and rows of a given worksheet. Tab movement generally goes from left to right across the screen, while Enter movement goes from top to bottom of a screen. To reverse the direction, or return to the previous cell, press Shift Tab or Shift Enter.
Arrow keys can also be used to move from one cell to the next. Multiple cell movement can be accomplished by using the Control key (Ctrl) with the arrow keys to move to the next cell containing text. Page Up and Page Down keys can also move through multiple cells. Finally, one can also move from one cell to another by moving the mouse pointer to the desired field and clicking the left mouse button.
The Esc key backs out of menu commands and cancels dialog boxes. Esc is a good key to press if what is happening on the screen is not desired.
All data in ISAT are entered in cells where information may simply be typed. Alternatively, typing the first few characters of the intended entry will cause the cell to automatically select the closest match from cells in the rows immediately above. This can prove to be problematic if an automatic entry does not reflect the intentions of the user. Care should be taken that any auto-population of cells is indicative of the user's intent. Finally, Excel spreadsheet software allows for use of Microsoft's standard copy and paste techniques. A user may select information to be copied by clicking and dragging over the desired text. Press Ctrl+C to copy the text, move to the field/site where the information is to be copied by clicking the mouse cursor in the field (or tabbing to it), and then press Ctrl+V to paste.
If an error is made while entering data, simply use the Backspace key to delete the error and then retype the value. To edit existing or incomplete data, click an insertion point in the desired field and use normal editing techniques to make the correction. This includes the Delete key, which removes the selected characters or characters to the right of the cursor. Entire blocks of cells may be cleared simultaneously by highlighting the cells and using the Delete key. However, if an entire row of information is no longer desired, do not delete the entire row. Calculations built into this program rely on the specific rows already in the program. Clearing information in cells rather than deleting them will preserve program integrity. This situation also applies to moving blocks of cell information by clicking and dragging. Once calculations have been performed and output reports generated, formulas may no longer be valid if cells have been moved.
Information entered into Excel spreadsheet software is not automatically saved by the program. The user must explicitly save entered information (see the Saving, Printing, and Clearing Data section).
Saving, Printing, and Clearing Data
ISAT estimates safety performance for an interchange based upon data supplied by the user. Interchange data sets are created by entering data, as described above. The input data entered for an interchange may be saved at any time for later retrieval using the File/Save menu buttons at the top of the screen. The data will be saved under a user-selected file name and location. When ISAT is restarted, any data used in the previous session will still be present.
A custom menu located on the first worksheet (i.e., Input-General) provides four utility macros to clear and print interchange data used in ISAT:
Modifying Calibration Coefficients and Crash Distributions
ISAT makes use of SPFs from previous and ongoing safety research. As such, the calculations of the program are not initially designed to be specific to a given highway agency. However, ISAT has calibration coefficients which provide the capability to adjust the calculations performed within ISAT to better reflect local safety experience. It is recommended that, before using ISAT to perform actual safety assessments, the user modify the default calibration coefficients to better reflect local safety experience. Then, it is recommended that the calibration coefficients be updated annually. Detailed procedures for calculating appropriate calibration coefficients are provided in the Calibration Coefficients section of this manual.
ISAT is designed to calculate crash frequencies for a defined set of collision types and crash severity levels. To calculate such frequencies, ISAT makes use of crash proportion distributions. Default distributions are provided within ISAT, based upon actual crash data from Washington State. Before using ISAT to perform actual safety assessments, it is recommended that the user modify the default crash proportions based upon local crash data to better reflect local safety experience. Then, it is recommended that these proportions be updated annually. Detailed procedures for calculating the crash proportions are provided in Crash Distributions by Severity and Type section of this manual.
Ending an Excel Spreadsheet Software Session
When work with Excel is finished, quit by clicking File Exit on the menu bar or by clicking the close button at the right end of the Excel title bar. Excel will prompt the user to save the worksheet for later retrieval.
Topics: research, safety, intersection safety, data and analysis tool
Keywords: research, safety, interchange, geometric design, safety performance function
TRT Terms: interchanges, highway design, highway safety, safety engineering