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South Dakota Department of Transportation
Project Synopsis

Title: 20-Year Traffic Forecasting Factors
Project Researcher: Christina Bennett, Office of Research
Project Manager: Dan Strand
Research Period: 5/1/1999 - 2/28/2000
Cost: $60,000.00

Problem Statement:The Office of Data Inventory is responsible for calculating 20-Year Traffic Forecasting Factors. These factors are used to estimate traffic volumes and the number of equivalent single axle loads (ESAL) for highway geometric and pavement design purposes. Presently, these factors are calculated for passenger and commercial vehicles on three functional classes for each of the six planning districts in South Dakota. At present these factors are computed once every four years.

The process of computing these factors is time consuming and labor intensive, but more importantly the accuracy of these factors are of greater concern. Some (but not all) of the reasons for their inaccuracy are:

  • they are not computed each year and therefore become outdated

  • there is no written procedure used to compute the factors which may cause inconsistent calculations

  • the traffic within the large planning districts may not be homogeneous causing some highways to be over- or under-designed

  • increases in the population are not considered

  • the Average Daily Traffic (ADT) is averaged over the entire state for each functional class

  • the rural traffic in counties that have a Municipal Planning Organization (MPO) may not be adequately considered - there is no procedure for handling the factors near the DOT/MPO interfaces

  • there may be other important variables that are not considered in the computations.

    Therefore, research is needed to develop and document a procedure and recommend software for computing 20-year traffic forecasting factors. The results of this research should improve the Departments confidence in the accuracy of its traffic forecasting.

    Findings: The investigations of the existing 20-year traffic forecasting procedure at the SDDOT included analysis of traffic data derivations, the sequence of events involved in the procedure, procedural components, automated processes, methodologies to produce forecasting factors, and coordination with Metropolitan Planning Organizations (MPOs) in the state. The findings led to the conclusion that implementation of the improved procedure will specifically address the SDDOT’s traffic forecasting needs. Implementation of the improved procedure is supported by additional recommendations that point to better traffic forecasting coordination with MPOs and ways to gain more procedural efficiency through software development. The recommendations have been prepared in expectation of immediate results, as well as the anticipation of long-term benefits from ongoing enhancements to coordinating activities with MPO's.

    Research Objectives:
    1  To document SDDOT’s current 20-year traffic forecasting procedure.
    2  To develop and document new procedures or processes that will enhance or replace SDDOT’s present traffic forecasting procedure.

    Research Tasks:
    1  Review and summarize literature relevant to traffic forecasting or traffic modeling.
    2  Meet with the technical panel to review the research topic and work plan.
    3  Document SDDOT’s present procedure, software, and data used to compute 20-year forecasting factors by interviewing necessary SDDOT personnel recommended by the technical panel.
    4  Summarize each MPO’s present traffic forecasting procedure as well as its forecasting coordination with DOT.
    5  Summarize the traffic forecasting procedures and data collection methods of other states. At a minimum, survey a representative sample of other rural mid-west states.
    6  Submit a technical memorandum which summarizes the findings of the literature review, survey of other states, interviews of department personnel, and preliminary recommendations for procedures, required data, and software which will improve South Dak
    7  Based on the tasks above and approval of the preliminary recommendations from the technical panel, develop and document a practical 20-year traffic forecasting procedure for SDDOT which will improve the accuracy of the computed forecasting factors.
    8  In conjunction with DOT’s Data Inventory and Planning & Programs personnel, use the recommended procedure to develop and validate 20-year traffic forecasting factors using DOT’s most recent data.
    9  Recommend coordination between the DOT and the MPOs for determining the forecasting factors.
    10  Recommend software and its functional requirements that will automate the 20-year traffic forecasting factor computations.
    11  Submit a final report summarizing relevant literature, forecasting methodology, interview and survey results, developed procedures, recommended software, conclusions, and recommendations.
    12  Make an executive presentation to the SDDOT Research Review Board summarizing the findings and conclusions.

    Documents Available:
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