1.2.7 Analysis Years and Peak Periods

Time (temporal) limits for an operational analysis include the analysis years and analysis periods. Typical analysis years often include the following:
  1. Existing Year – Existing year analysis represents the current conditions analysis and is typically completed using data less than three years old. If the project is using data more than three years old, include verification about how the volumes represent existing conditions.
  2. Opening Year – The opening year is the first year in which the proposed improvements are expected to be open to traffic. If the project is proposed to be implemented in phases, the opening year is the year the first phase of traffic will be opened to traffic. The opening year is typically determined by project size, complexity, and schedule, with respect to the letting date. The let date is defined as the official receipt and opening of bids and determination of the apparent low bidder. It is dependent on the planning and programming of projects.
  3. Interim Year – An interim year is the opening year of different phases of the project after the first phase. Interim years are sometimes used if the proposed improvements show failing level of service prior to the design year.
  4. Design Year – Projects are planned and designed to meet the future, anticipated needs and characteristics of a certain year. This is referred to as the design year. Typically, the design year is 20 years after the anticipated project opening year.
The analysis years listed above are typical, but can vary based on project type (e.g., resurfacing, restoration, or rehabilitation projects often have analysis years of five to 10 years). Pavement design year is used for traffic projections but is not needed for traffic analysis. It is typically 10 years after the design year and represents useful life of the pavement. The analysis period is the time of day when the analysis will be conducted.
Typical traffic analysis time periods (temporal limits) include a weekday AM peak and a weekday PM peak. There are situations that warrant different analysis periods (e.g., analysis of a facility near a school, mall, or sports arena; analysis of a facility with heavy weekend traffic). Part of the scoping process is identifying the analysis day(s) and the analysis periods (e.g., AM Peak: Tuesday-Thursday, 7:15AM – 8:15AM).
Temporal limits for a historical safety analysis typically include the most recent three to five years. Temporal limits for a predictive safety analysis typically include the opening and design years. For projects that need FHWA approval, request Crash Records Information System (CRIS) data through TxDOT's Traffic Safety Division (TRF) or the Design Division.
Below are sample prompts that may provide guidance on selecting temporal limits:
  • What are the analysis years for each study area?
  • What are the analysis periods for the study?