Automated Vehicle Control Algorithms and their Influence on Traffic

Principal Investigator

Rajesh Rajamani, Professor, Mechanical Engineering


  • David Levinson, Professor, Civil, Environmental and Geo-Engineering
  • Panos Michalopoulos, Professor, Civil, Environmental and Geo-Engineering

Project Summary

Adaptive cruise control (ACC) systems are currently being developed by many automotive manufacturers around the world. These ACC systems enhance cruise control by adding the ability to automatically maintain a desired spacing (constant time gap) with respect to a preceding car that has been detected in the lane. However, current ACC systems have been primarily designed from the perspective of driver comfort; they suffer from several shortcomings when issues of safety and traffic flow are considered. The results of this study resolve the controversy over the stability of constant time-gap policy for highway traffic flow. While previous studies left doubt as to the effectiveness of constant time gap policies and whether they maintain stability in all traffic conditions, this study proved that the constant time gap policy is in fact stable to a limit. At this limit, depending on the boundary conditions, conditions lose their stability. This study developed alternative ways to maintain the balance between safety and traffic flow for ACC vehicles that does not rely on constant time-gap policies. New spacing policies will create more stability, and therefore safer conditions, and allow for greater traffic capacity.


  • ITS Institute (RITA)

Project Details

  • Start date: 08/2000
  • Project Status: Completed
  • Research Area: Transportation Safety and Traffic Flow
  • Topics: Intelligent Vehicles, Traffic Modeling and Data, Traffic Operations

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