Highway Capacity Manual (HCM) Capacity Adjustment Factor (CAF) Development for Connected and Automated Traffic at Signalized Intersections

Connected and Automated Vehicles (CAVs) will potentially improve transportation system performance. Guidance on capacity impact of CAVs at different market penetration rate (MPR) will help agencies to incorporate the effects of CAVs while planning and designing roadways. Traditionally, practitioners use the Highway Capacity Manual (HCM) to assess capacity and evaluate the quality of service for various facilities and systems. While several studies provide insights into the capacity benefits of CAVs, there is a need to quantify CAV effects that can be used to develop HCM guidance. This study estimates the capacity benefits of CAVs at signalized intersections and develops capacity adjustment factors (CAFs) for the HCM. The researchers considered variations in CAV gap/headway settings, platoon lengths, turning movement types (through and left), and left-turn phasing modes (protected versus permitted). Microscopic traffic simulation is used to model CAVs. Results show that performance indicators such as saturation headway gradually improves with increase in CAV MPR, resulting in up to 40% capacity increase at 100% MPR for the protected movements.  For permitted left turns, up to 45% capacity increase could be achieved at 100% MPR. This increase in the permitted left turn capacity is attributed to the vehicle-to-vehicle (V2V) communication that provides advanced information on available gaps in conflicting traffic and reduced follow-up headway time both for the permitted left-turn and the opposing through movement. Based on the capacity results, this paper provides CAF tables for CAVs that can be easily integrated into the HCM and used for planning level guidance by practitioners.


  • English

Media Info

  • Media Type: Web
  • Features: Figures; References; Tables;
  • Pagination: 20p

Subject/Index Terms

Filing Info

  • Accession Number: 01764014
  • Record Type: Publication
  • Report/Paper Numbers: TRBAM-21-03049
  • Files: TRIS, TRB, ATRI
  • Created Date: Dec 23 2020 11:17AM