6. Slow Zones : This approach is a community-based program to set lower speed limits for specifically designated corridors or areas than the speed limits on surrounding roadways of the same type. For example, New York City has implemented a “Neighborhood Slow Zones Program” to reduce crash frequency and severity and to enhance quality of life by reducing cut-through traffic and traffic noise in residential neighborhoods. Within the 6 Slow Zone area, speed limits are reduced from 25 mph to 20 mph, and traffic calming treatments are added with the intention of changing driver behavior Based on its review of existing speed limit setting practices and factors that were identified that influence operating speed and safety, NCHRP 17-76 developed the Speed Limit Setting (SLS)- Procedure. The SLS-Procedure is designed to apply a set of unique decision rules that consider both driver speed choice and safety to four collapsed Speed Limit Setting Groups (SLSGs): Limited-Access, Undeveloped, Developed, and Full-Access facilities based on roadway types and roadway contexts. The measured operating speed is recommended as the starting point for selecting a posted speed limit using the SLS-Tool, the spreadsheet that accompanies the SLS-Procedure. The tool suggests a speed for a roadway segment based on existing conditions and crash experience, as illustrated in Figure 2 Safety is evaluated using crash data, risk factors, and research linking geometric variables to crash frequency.
Figure 2: Overview of procedure to calculate suggested speed limit (NCHRP Research Report 966, 2023)
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