BACKGROUND: Annual average daily traffic (AADT) which represents traffic on a typical day of the year is used by transportation agencies for reporting requirements, allocating resources, informing decision-making, and supporting various agency functions. Transportation agencies use different methods to derive AADT estimates from short-duration counts of traffic data from permanent and portable traffic counting equipment installed at selected locations.
Commonly used methods for estimating AADT do not adequately address how short-duration counts should be assigned to adjustment factor groups. Also, there are concerns about the inherent errors in these methods, their applicability to roadways with insufficient traffic data, and the accuracy of the derived AADT estimates. There is a need to improve existing methods and develop new methods for functional classes of roadway where insufficient continuous counting exists to improve accuracy of AADT estimates. These methods will help transportation agencies improve the quality of traffic information and support the decisions regarding capital investment programs and budgets as well as design and maintenance programs.
OBJECTIVE: The objective of this research is to develop rational methods for assigning short-duration traffic volume counts to adjustment factor groups for estimating AADT. The research is concerned with all functional classes of roadways and traffic volumes.
Accomplishment of the project objective will require the following tasks.
PHASE I: (1) Collect and review relevant domestic and foreign literature, research findings, and information relative to the methods for assigning traffic volume counts to adjustment factor groups for estimating AADT. This information may be obtained from published and unpublished information, and contacts with public and private organizations. Based on this review, identify and evaluate available methods. (2) Identify and prioritize the weaknesses and gaps in the methods identified in Task 1 for further consideration/investigation in Phase II to (1) improve existing methods and (2) develop new methods for functional classes of roadway where insufficient continuous count data exists. (3) Based on the evaluation performed in Task 2, prepare an updated, detailed work plan to be executed in Phase II that includes an approach for investigating the recommended items and developing validated methods for assigning traffic volume counts to adjustment factor groups for estimating AADT. (4) Prepare an interim report that documents the research performed in Tasks 1 through 3. Following review of the interim report by the NCHRP, the research team will be required to make a presentation to the NCHRP project panel. Work on Phase II of the project will not begin until the interim report is approved and the Phase II work plan is authorized by the NCHRP. The decision on proceeding with Phase II will be based on the contractor’s documented justification of the updated work plan.
PHASE II: (5) Execute the Phase II plan approved in Task 4. Based on the results of this work, propose improved and new methods for all functional classes of roadways and traffic volumes. Also, illustrate use of the proposed methods to obtain realistic estimates of AADT with case examples covering a range of functional classes of roadways and traffic volumes. (6) Prepare a final deliverable that documents the entire research effort. The proposed methods shall be presented as a stand-alone deliverable in a format suitable for consideration and adoption by AASHTO with the examples as appendices.
Status: Research in progress.