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FHWA Highway Safety Programs

USLIMITS2 - Frequently Asked Questions

Q: Were any national associations such as AASHTO and ITE involved in the development of USLIMITS2?

A: The expert system was developed under the National Cooperative Highway Research Program (NCHRP) which is sponsored by AASHTO. A project panel made up of 3 State members, an ITE representative, and a county representative oversaw the development. In addition to the project panel, the research team used a core group of experts to identify key factors and decision rules through a series of panel meetings and case studies. The core group consisted of two state engineers, two city engineers, two county engineers (one which was a member of the ITE traffic engineering council), and two police officers (1 county and 1 city). An expanded panel consisting of state and district traffic engineers (60), city engineers (49) and county engineers (20) provided input on specific topics and completed case studies used in developing the decision rules. It was further enhanced through funding from the Federal Highway Administration. From 2006 until 2012, USLIMITS was hosted on a server at the University of North Carolina Highway Safety Research Center. In 2012, it was moved to a server at the Federal Highway Administration.

Q: Have any state DOTs, FHWA or AASHTO adopted USLIMITS2 as an acceptable tool for determining speed limits?

A: In 2008, USLIMITS was approved by FHWA and AASHTO as a priority market ready technology and innovation. In 2012, FHWA began hosting USLIMITS2 and promoting its adoption. We know that many states and local agencies are using USLIMITS2. The Wisconsin Statewide Speed Management Guidelines recommends that USLIMITS be used in the development of any revised speed limit recommendation. The Wyoming Traffic Studies Manual (2011) refers engineers to USLIMITS for help in determining appropriate speed limits.

Q: Can USLIMITS2 be used for sites outside the USA?

A: USLIMITS2 was specifically developed for use in the United States and does not currently work with metric units. All recommended speed limits are in five mile per hour multiples. However, it can be used for sites outside the United States if the decision rules are applicable to the specific location. The user would have to manually convert the recommended limits to km/h.

Q: How do I save my project data?

A: To save project data entered into USLIMITS, select the "Save Project File" button near the bottom of the USLIMITS output screen. If you are asked: Do you want to open or save this file? Select "Save", then specify the folder where you want to save the file. This saved file is an encrypted record of the data entered that can be opened in USLIMITS to make updates or revisions. Project data and results can be saved in a Word document by selecting "Create MS Word Report". The Word document file cannot be opened or used by USLIMITS to revise or update your project.

Q: I saved the project file but can't find it. Where are project files saved?

A: In Windows, the project file is normally saved in your Downloads folder but the location may vary since it is determined by settings of the browser (Internet Explorer, Firefox, Chrome, etc) used to access USLIMITS. The default file name is the Project Name with the date appended and has a "txt" extension. If you enter *.txt in the Windows search box, it should provide you with a a list of all USLIMITS project files on your computer and their location.

Q: When entering the traffic accidents and injuries I could not input more injuries than accidents. In some accidents you have more than one injury.

A: The program asks for the number of injury crashes, not the number of injuries. The number of injury crashes will always be less than or equal to the total number of crashes.

Q: Users are asked to input total injury and fatal crashes. The Users Manual is not clear if these are minor and major injury, any and all injuries, or major injury crashes only. Am I correct in assuming total injury means any and all injury crashes on record? Our concern is the reporting of minor injury crashes is less dependable than major injury crashes.

A: This program was developed based on input from practitioners and researchers, and a decision was made while developing the program to use all injury and fatal crashes. If you want to enter only major injury crashes, you can do so, but make sure that you enter the average number of the same type of crashes for similar roads in the next input screen, rather than use defaults which are based on all injury and fatal crashes from state data in FHWA's Highway Safety Information System.

Q: I get a Page Not Found Error after entering crash data. What can I do to finish the USLIMITS analysis?

A: In earlier versions of USLIMITS, entering the crash AADT with a comma separator or entering annual traffic instead of daily traffic would cause USLIMITS to crash and generate this error message. In Version 2.2, USLIMITS was revised to accept traffic volume input with or without the comma separator. Also, an error check was added to warn users when the value entered for AADT was excessive for the selected road type.

Q. When entering number of driveways and intersection access points, do I count each 4 leg intersection as one or two access points?

A: Each side street approach is counted as an access point, so a 4-leg intersection should be counted as 2 access points and a T-type intersection as 1 access point.

Q: How do I get more information about the program, i.e., the logic and decision rules?

A: In the upper right corner of each USLIMITS web page, there is a link labeled "HELP". By clicking on HELP you will be taken to a page that that provides information about the decision rules and the user guide. In addition, each input page has "more info" links that provide information about the specific data items being requested.

Q: Is it possible to get a desktop version of the program which I can install on my computer?

A: There is no desktop version of the program. This program was created specifically to be used as an Internet application.

Q: Are Consultants allowed to use this program for commercial purpose?

A: There are no restrictions on using USLIMITS2 for commercial purposes.

Q: How are project data used by FHWA or others after data entry by a highway agency? Are data stored or saved for future research or processing by others?

A: With the current version of the program on the FHWA site, all data are stored locally on the user's computer or network and cannot be accessed by FHWA or others. An earlier of version of the program which stored projects on the web server was used by FHWA to monitor the number of users and projects in order to measure progress in meeting deployment goals.

Q: Who do I contact to report issues or make suggestions for improving USLIMITS2?

A: Send an email to to report problems encountered using USLIMITS2 or to suggest new features and enhancements that you would like to see incorporated in a future release.