Speed Harmonization and Queue Warning may reduce extreme, unsafe speed drops with average speeds reduced by up to 20 percent.
An extensive analysis of a Prototype was performed to evaluate the operational conditions under which Speed Harmonization and Queue Warning applications are most beneficial.
Made Public Date


San Mateo
United States

Impacts Assessment of Dynamic Speed Harmonization with Queue Warning

Summary Information

The goal of the Intelligent Network Flow Optimization (INFLO) application bundle within the Dynamic Mobility Applications (DMA) Program is to optimize traffic flow through the use of connected vehicle-drawn data. An evaluation was performed to assess the impacts of a prototype of Dynamic Speed Harmonization (SPD-HARM) with Queue Warning (Q-WARN), two component applications of the INFLO bundle.


A previously calibrated VISSIM microsimulation model of an 8.5-mile segment of US-101 freeway in San Mateo, California was used for a "before and after" analysis.
  • Modeling was done for six operational scenarios for each of the four different levels of connected vehicle response rates: 0-percent (baseline), 10-percent, 25-percent, and 50-percent (a maximum of 50-percent was used with the implicit assumption that the response rate is the market penetration rate depreciated for communication loss and driver compliance effects.)
  • The six scenarios modeled combined a flat median traffic demand level, three possible severity levels of incidents (none, 1 lane closed – 30 min, 1 lane closed – 60 min) and two possible weather types (dry pavement, wet pavement) for the corridor.
  • Simulation runs were averaged for each scenario and results were then weighted according to their expected frequency over the course of a year to obtain annualized results.
Travel-time, demand and incident data for the year 2012 were obtained from the Caltrans PeMS (Performance Measurement System) database. Weather data for the year 2012 was extracted from the University of Utah's online weather database.

  • The magnitudes of the speed drops (shockwaves) between vehicles was significantly reduced, even at the 10-percent market penetration level.
  • Under SPD-HARM, average speeds on freeways were reduced by up to 20-percent, with the greatest impact occurring at the 50-percent connected vehicle level.
  • Under severe-congestion conditions (such as during lane-closure incidents), reductions in speed still occurred with the Prototype, but they were less significant than for less-severe conditions.
  • There was relatively little effect on vehicle stops.
  • There was an increase in the amount of lane changing on the freeway.
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