Estimating HCM Default Parameters for Louisiana

Details

• Creators:
  Rahman, M Ashifur ; Moomen, Milhan ; Junaed, Siam
• Corporate Creators:
  Louisiana Transportation Research Center
• Corporate Contributors:
  Louisiana. Department of Transportation and Development ; United States. Department of Transportation. Federal Highway Administration
• Subject/TRT Terms:
  Headways Highway Capacity Saturation Flow Signalized Intersections
• Publication/ Report Number:
  FHWA/LA.25/715
• Resource Type:
  Tech Report
• Geographical Coverage:
  Louisiana;United States
• Edition:
  Final Report
• Corporate Publisher:
  Louisiana Transportation Research Center
• Abstract:
  Although the Highway Capacity Manual (HCM) provides default values for its methodologies, it also states that these values represent typical national values and that conditions within a state, region, or community may differ. When default values are applied frequently in analyses, the use of local default values can reduce the uncertainty in the analysis results. This study addresses the need for accurate intersection capacity analysis in Louisiana, where reliance on default Highway Capacity Manual (HCM) values can lead to inefficiencies due to regional variations in traffic conditions. The research focused on estimating key traffic flow parameters: base saturation flow rate (BSFR) for signalized intersections, and critical headway (CH) and follow-up headway (FH) for two-way stop-controlled (TWSC) intersections. A comprehensive database for signalized and stop-controlled intersections was developed by integrating data from multiple sources, including the extensive traffic data collection 511 system, highway database, and DOTD representatives. The study analyzed 51 signalized intersections, adjusting for factors such as lane width, heavy vehicle presence, and turning movements. This resulted in a statewide BSFR of 1,655 pc/h/ln, lower than the HCM default. Significant regional differences were observed, with district-specific BSFRs ranging from 1,537 pc/h/ln to 1,773 pc/h/ln. For TWSC intersections, data from 26 four-leg intersections were used to estimate CH (7.1 to 10.1 sec.) and FH (5.9 to 6.5 sec.), which were both substantially higher than HCM defaults, reflecting conditions at low-volume minor roads. The study highlights the limitations of applying national default values and emphasizes the importance of using locally estimated parameters for more effective traffic management. The findings support the adoption of district-specific BSFRs for signal timing and capacity analysis, as well as the application of the estimated CH and FH values for TWSC intersection design, with appropriate HCM adjustments.
• Format:
  PDF
• Funding:
  23-3SS;1000459
• Collection(s):
  US Transportation Collection
• Main Document Checksum:
  urn:sha-512:12f04a1d0eb37c8ae97f53101838ba966aa4b20055814a2ef9bc50aa77f70a32774597c5d6dd8a23d318f583379d4debc9bad493c7c8025a4fe3c15553b10f37
• Download URL:
  https://rosap.ntl.bts.gov/view/dot/86117/dot_86117_DS1.pdf
• File Type:
  [PDF - 3.01 MB ]