UNIT 2: ROADWAY SAFETY
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Posted speed limits are often the same as the legislative statutory speed limit. Agencies with designated authorities to set speed limits, which include States, and sometimes local jurisdictions, can establish non-statutory speed limits or designate reduced speed zones, and a growing number are doing so. While non-statutory speed limits must be based on an engineering study, conducted in accordance with the Manual on Uniform Traffic Control Devices (MUTCD) involving multiple factors and engineering judgment, FHWA is also encouraging agencies to use the following:
Expert Systems tools.
USLIMITS2
A Tool to Aid Practitioners in Determining Appropriate Speed Limit Recommendations
– FHWA offers FREE technical assistance to State and local agencies that are interested in learning more about using USLIMITS2 or setting safe speed limits. This includes answering questions, providing in-person workshops, providing virtual workshops held via web conference, and giving presentations. To request technical assistance, send an email to help@uslimits.org
– USLIMITS2 is a web-based expert system tool designed to help practitioners with conducting an engineering study for setting reasonable, safe, and consistent speed limits for specific segments of roads
– USLIMITS2 was developed based on research through National Cooperative Highway Research Program (NCHRP) Project 3-67. An expert panel, comprised of experienced traffic engineers and other subject matter experts, provided input to the development of the decision rules and logic flow employed within the tool. USLIMITS2 considers all major factors used by practitioners to make engineering judgment in determining an appropriate speed limit. This includes: operating speed (50th and 85th percentile), annual average daily traffic, roadway characteristics and geometric conditions, level of development in the area around the road, crash and injury rates, presence of on-street parking, and extent of ped/bike activity, as well as several others depending on the road type. For detailed information on the input factors and the expert system decision rules, please refer to the User Guide, NCHRP 3-67 report, and Decision Rules documentation.
– USLIMITS2 is applicable to all types of roads; however, it is not applicable to school zones, construction zones, or roads with variable speed limits that are raised or lowered based on weather, traffic conditions, or other factors. Engineering experience and knowledge should be used in collecting the required information and when interpreting the results.
• For help with using USLIMITS2 or questions about setting appropriate speed limits, please email help@uslimits.org.
• Disclaimer: The U.S. Government assumes no liability for the use of the information contained in this tool. This tool does not constitute a standard, specification, or regulation.
USING USLIMITS2
Create a new project
Revise an existing project
– Before beginning a new project, it is recommended that you read through the User Guide and be prepared to enter the necessary data (e.g., 50th and 85th percentile speed, roadway characteristics, and crash history). If the segment you are studying is a new route, the system will not require this data, but it is recommended that the statutory speed be posted on new routes until such time that reliable data on operating speed, crashes, and other factors can be collected.
– After entering all project information you will have the opportunity to save the recommendation report. You also can save the project file and upload it in the system at a later time to revise your project if needed.
– To understand how USLIMITS2 arrived at the recommended speed limit, review the Decision Rules.
TECHNICAL SUPPORT
If you have any questions about USLIMITS2 or setting safe speed limits, or experience any technical difficulties while using this program, find any bugs, or have suggestions for improving USLIMITS2, please send an email to help@uslimits.org.
• NCHRP 966: Posted Speed Limit Setting Procedure and Tool
• Safe System approach.
Based on international experience and implementation in the United States, the use of 20 mph speed zones or speed limits in urban core areas where vulnerable users share the road environment with motorists may result in further safety benefits.
Considerations
When setting a speed limit, agencies should consider a range of factors such as pedestrian and bicyclist activity, crash history, land use context, intersection spacing, driveway density, roadway geometry, roadside conditions, roadway functional classification, traffic volume, and observed speeds.
To achieve desired speeds, agencies often implement other speed management strategies concurrently with setting speed limits, such as self-enforcing roadways, traffic calming, and speed safety cameras. Additional information is in the following FHWA resources:
Speed Management
Speeding - traveling too fast for conditions or exceeding the posted speed limits - is a contributing factor in 26 percent of all fatalities. In 2020, there were 38,824 fatalities on our Nation's roadways, of which 11,258 were speeding-related - increased by 17 percent from the previous year. Speeding is a safety concern on all roads and for all road users. Although much of the public concern about speeding has been focused on high-speed Interstates, only 14 percent (1,344) occurred on interstate highways, rural and urban combined, while 86 percent of speeding-related fatalities occurred on non-interstate roadways. Speeding is a complex issue involving engineering, driving behavior, education, and enforcement. FHWA is the lead agency accountable for the engineering actions.• Self-Enforcing Roadways: A Guidance Report.
• Noteworthy Speed Management Practices.
• Jurisdiction Speed Management Action Plan Development Package.
• Traffic Calming ePrimer.
Roadway design and other infrastructure factors play a significant role in managing speeds and can deter excessive speeding behaviors from occurring in the first place.
Key Departmental Actions to Enable Safer Speeds
