This paper describes the development of USLIMITS2, a knowledge-based expert system that can be used by decision-makers to aid in the selection of a safe and operationally efficient speed limit for speed zones on all road systems in the United States. The expert system is based on the results of previous research including feedback from users of the current USLIMITS program developed by the Australian Road Research Board, an examination of current speed zoning practices, and the need to improve and aid practitioners in recommending appropriate speed limits for specific road and traffic conditions. USLIMITS2 is a web-based application that can be accessed by anyone with a computer with web-browsing software and access to the Internet. In addition to the program, the web site, www2.uslimits.org, also contains a copy of the research report, the decision logic, and a User Guide to assist the user through the decision-making process.
The system was designed to be user friendly and not require intensive data collection and analysis. Emphasis was placed on having the system explicitly consider safety along with other factors in the speed limit decision process. The tool was specifically developed to provide expert resource information based on logic used by experts in the United States. The system does not provide recommendations for statutory limits or temporary limits such as those posted in work zones and school zones.