Define RRP and Exclude Delays

– Define the duration of the RRP (typically one calendar year to incorporate all day-today and month-to-month variability in the various factors that impact travel time reliability). Identify which days of the week to include or exclude in the analysis, such as weekdays, weekends, and holidays.

Gather Reliability Inputs

– Collect the inputs necessary for conducting a reliability analysis, including demand variability, weather data, incident records, work zone data, and special event information.

Define or Refine Global Inputs

– Two global calibration parameters that may require revision are facility-wide jam density and queue discharge capacity drop. These global parameters apply to the entire facility, as opposed to other parameters that exist at specific locations or segments along the freeway.

Define Number of Replications for Reliability Analysis

– Define the number of replications used to generate scenarios (typically four for a RRP of one year) to obtain a sufficient, randomly generated sample size of data.

Define Demand Variability by Day and Month and Assign to Scenarios

– Define Traffic and Safety Analysis Procedures Manual | 2024 15-18 the demand multipliers by day of the week and by month of the year based on facility-specific data.

Define Weather Probabilities and Impacts and Assign to Scenarios

– Define the probabilities of occurrence of each of the weather categories and the corresponding capacity, demand, and SAFs.

Define Incident Frequencies and Impacts and Assign to Scenarios

– Define the incident frequencies for each of the incident severity types, the corresponding capacity, demand, and SAFs, and number of lanes lost due to the incident.

Define Short-Term Work Zone Events and Adjustments

– Define the dates of any short-term work zone events, the corresponding capacity, demand, and SAFs, and number of lanes lost due to the work zone. “Short-term work zones” refers to scheduled or planned work zones that are not operating for the entire RRP. Long-term work zones are often evaluated as a stand-alone reliability analysis, with a base scenario modified with the work-zone characteristics.

Generate Full Scenario List and Scenario Probabilities

– Use a computational program or software (FREEVAL-ATDM, Active Demand Management Capability Maturity Framework Tool, etc.) to automatically generate a list of all scenarios for the reliability analysis. Each scenario has a complete set of attributes defining the demand, capacity, and travel speed characteristics of that scenario relative to the base scenario.

Perform Analysis for Each Scenario

– Use a computational program or software to automatically apply the adjustment matrices from the previous step to the base scenario. Each resulting scenario is evaluated with the HCM freeway capacity analysis core methodology. The computation program calculates and catalogs performance measures for each scenario.

Compute Reliability Performance Measures

– Generate a travel time distribution from the average facility travel times by analysis period and scenario. The computational program or software can automatically compute a variety of reliability performance measures from the results of all scenarios.

Validate Against Field Data

– Compare the reliability results to the field data from another model to determine whether the model matches the field data in an acceptable way or whether the analysis involves calibration adjustments.

Report Performance Measures

– Report the facility’s reliability performance measures. An ATDM evaluation may be performed to continue the analysis.