Engineering Speed Limits
The management of speed through appropriate speed limits is an essential element of highway safety. Appropriate speed limits are a prerequisite for effective and sustainable speed management. In terms of traffic law, speed limits should reflect the maximum reasonable and safe speed for normal conditions. That is speed limits should be acceptable as reasonable by most drivers and separate high and low risk speed behavior. If lower speed limits are desired, then engineering and other measures should be implemented that reduce speeds to a level that would support a lower limit.
Manual on Uniform Traffic Control Devices
The Manual on Uniform Traffic Control Devices (MUTCD) is the national standard for signing on all highways. Sections 2B.13-16 address regulatory speed limits and Section 2C addresses advisory speed signs. School zone speed limit signs are discussed in Section 7B and work zone speed limits in Section 6C.
USLIMITS2 is a web based tool designed to help practitioners set credible and consistent speed limits for specific segments of roads. It is applicable to all types of roads ranging from rural local roads and residential streets to urban freeways. The original USLIMITS was developed under NCHRP Project 3-67 in 2006. FHWA recently adopted the program with enhancements and made it available with user/customer support on the FHWA server at http://safety.fhwa.dot.gov/uslimits/.
User-friendly, logical, and objective, USLIMITS2 is of particular benefit to local communities and agencies without ready access to engineers experienced in conducting speed studies for setting appropriate speed limits. For experienced engineers, USLIMITS2 can provide an objective second opinion and increase confidence in speed limit setting decisions. Users input factors including route type, section length, annual average daily traffic, 50th and 85th percentile speeds, statutory speed limit, and terrain, among others. They receive a recommended speed limit and a list of issues that might be further investigated. Users can save their project file and/or create Word and Excel versions of their reports.
Demonstration Projects on Setting And Enforcing Rational Speed Limits
NHTSA and FHWA are jointly supporting efforts in seven states to demonstrate and evaluate an integrated "three E's" (engineering, enforcement, education) approach to the management of speed and crash risk. Rational speed limits are established on the basis of an engineering study of prevailing speed and other factors such as pedestrian activity and crash history. The 85th percentile speed is typically used as a starting point for setting a rational limit but it may be set as low as the average speed based on other factors. Once the speed limits are appropriately set and the judiciary informed, a program of strict enforcement with a low tolerance for speeds exceeding the limits is combined with PI&E explaining the purpose of the revised limits and the consequences for violators. Evaluation of program effectiveness is a critical element of the demonstrations. A list of our primary partners and the location of the demonstration roads are listed below.
Analysis of Speeding-Related Crashes (PDF 594 KB)