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Neighborhood Traffic Management Program (NTMP)

Tools to Address Speeding and Traffic Volumes

Half Closures and Semi-Diverters

Top view of a street with semi-diverter

Semi-diverters are extensions from the curb or islands - usually extending from a corner of an intersection that block one directional lane of the street.

They are used to prevent drivers from making certain turn movements at an intersection. Semi-diverters can effectively reduce traffic volumes on a street although the diverted traffic may impact adjacent streets. Semi-diverters are very effective in reducing volumes at specific locations.

Semi-diverters affect all drivers, including local residents. Thus, care must be taken to consider the impacts on alternative routes as well as neighborhood access routes.


Temporary Installation

Culver City, CA

Semi-diverter permanent installation

Permanent Installation


  • Reduces traffic volume.
  • Maintains access for residents.
  • Reduces cut-through traffic.
  • Reduces crossing distance for pedestrians.
  • Landscaping possible.
  • OK for emergency vehicles.
  • Can provide 2-way access for bicycles.


  • May divert traffic to parallel streets.
  • May increase trip length for some residents.
  • 1-2 curbside parking spaces lost.
  • Maintenance needs if landscaped.
Summary of Effectiveness
Volume Reduction Yes
Speed Reduction Yes
Safety Improvement Unknown
Streets to Use On Collector, Local Local/Collector
Use on Bus Route Possible
Use with Curbs and Gutters Yes
Spot or Area-wide Use Spot
Emergency Service Access Issues Yes
Impacts on Arterials Possible
Change in % Truck Unknown
Environmental Changes Unknown
Dependence on enforcement Some
Level of Violation N/A
Aesthetics and Landscaping Possible