A Variable Speed Limit System (VSL) should be considered for deployment as part of a project’s temporary traffic-control plan when the following conditions are anticipated:

  • The work zone will cause 10 minutes or more of additional travel time.
  • The work zone queue is estimated to slow traffic at least XX mph below the posted speed limit.


When properly designed and deployed for a specific project, a VSL System should advise drivers of an appropriate vehicle speed to allow them to travel through the work zone with minimal braking. The system determines the average speed of downstream traffic and advises upstream traffic of an optimum speed to approach the queue. It is anticipated that the system will smooth the transition between faster and slower moving traffic and provide an increase in capacity on the roadway through the work zone area.


Deployment criteria and anticipated effects are suggestions that were provided by the MnDOT 2007/2008 report “Minnesota Intelligent Work Zone Toolbox.”