1. (a)

   1. (1) Traditionally, the design year reflects a twenty-year horizon from the anticipated opening date of the project.
   2. (2) A minimum design year based on twenty (20) years following the approval of the plans, specifications, and estimates for a project is required by 23 U.S.C. § 109(b), which states:
2. (b) The geometric and construction standards to be adopted for the Interstate System should be those approved by the Secretary in cooperation with the State transportation departments. Such standards, as applied to each actual construction project, should be adequate to enable such project to accommodate the types and volumes of traffic anticipated for such project for the twenty-year period commencing on the date of approval by the Secretary, under section 106 of this title, of the plans, specifications, and estimates for actual construction of such project.

3. (b)

   1. (1) According to AASHTO’s Geometric Design of Highways and Streets (2004), the thirtieth highest hourly volume (30 HV) in the design year is recommended for design.
   2. (2) If year-round traffic counts are available from a nearby count station, it should be utilized to estimate the thirtieth highest hourly volume (30 HV).
   3. (3) If not, it is recommended that at least two (2) typical weeks of traffic data should be obtained for each ramp, crossroad, frontage road, freeway main lanes, etc., as appropriate.
   4. (4) One day’s worth of turning movement counts per intersection may be sufficient, however, in many cases it will not.
   5. (5) A traffic data collection plan should be discussed during early coordination.

4. (c)

   1. (1) In addition to the existing and design years, interim years may need to be considered resulting from:

      1. (A) Phased construction;
      2. (B) Changes in land use; or
      3. (C) Other projects within the study area.
   2. (2) With construction phased over an extended period of time, analysis should be provided for each phase to evaluate operations until the next phase will be implemented.

5. (d)

   1. (1) Recognizing that congested conditions may extend beyond a single hour in some cases, analysis of the peak hour may not be adequate for the operational analysis.
   2. (2) For locations and conditions in which a facility is at or near capacity today or in the future, a multi-hour time period would likely be required for proper analysis.
   3. (3) As depicted in Figure 3, while the peak period and peak hour relate to each other, the average speed and traffic flow vary within each and have different maximums and minimums.

Codification Notes: “AASHTO” means American Association of State Highway Transportation Officials. Source: Traffic Analysis Toolbox Volume IV: Guidelines for Applying CORSIM Microsimulation Modeling Software, January 2007 Figure 3. Selecting a Peak Period for Analysis