North Carolina Forecasts for Truck Traffic

North Carolina has experienced significant increases in truck traffic on many of its highways. Yet, current NCDOT project-level highway traffic forecasts do not appropriately capture anticipated truck traffic growth. NCDOT methods forecast total traffic AADT based on historical trends and assume base year and future year truck percentages are the same. Also, NCDOT determines the growth factor of historical AADT traffic data by looking only at the first year and the last year ignoring intermediate year traffic data. This research recommends that traffic for dual axle (Dual) trucks and tractor trailer (TTST) trucks be separately forecast using an average growth factor (AGF) method that uses all available data and calculates growth factors year by year and averages them for the historical trend. The results of this research propose statistical methods to separately estimate growth factors for light vehicles (Cars), Duals and TTSTs. In this study Cars represent FHWA vehicle classes 1-3, Duals 4-7 and TTSTs 8-13. The methods have modest data requirements based on NCDOT traffic counts and VTRIS on-line traffic data. Statistical guidelines include mean AGFs and confidence intervals to help refine the estimates for growth factors by vehicle class and highway type. Case study examples demonstrate the methods and guidelines for Interstate, US, and NC highways. Other issues are explored including the effects of increased truck traffic on highway level of service and pavement design.


  • English

Media Info

  • Media Type: Web
  • Edition: Final Report
  • Features: Appendices; Figures; References; Tables;
  • Pagination: 198p

Subject/Index Terms

Filing Info

  • Accession Number: 01152603
  • Record Type: Publication
  • Report/Paper Numbers: FHWA/NC/2006-28
  • Created Date: Feb 26 2010 12:05PM