The freeway capacity analysis analyzes 15- minute periods of extended lengths of freeway comprised of continuous connected basic freeway, weaving, merge, and diverge segments. A base dataset provides all the necessary input data for the freeway facilities core methodology, including the facility’s geometry, free-flow speeds, lane patterns, segment types, and base demand volumes. This initial freeway capacity analysis produces a base scenario model for the freeway reliability analysis.

A freeway’s performance is typically analyzed under different conditions to get a more accurate picture of the facility’s operations throughout the study period. Therefore, after a base scenario model is developed, a set of scenarios is created by modifying the base dataset inputs and applying adjustments, including CAFs, speed adjustment factors (SAFs), and demand adjustment factors (DAFs), associated with various factors that impact freeway capacity, such as weather events, traffic incidents, and work zones. These scenarios are generated to reflect conditions that a freeway facility experience during the RRP. Each scenario represents a single study period with adjusted demand and capacity variations specific to that scenario.

The default number of scenarios generated in a typical freeway reliability analysis, without considering weekends, is 240. This value was obtained by creating four replications of each weekday-month demand combination. Analyzing multiple replications of each weekday-month combination confirms the presence of a large sample of weather and incident events. The number of scenarios can be fewer or greater, depending on the scope of the analysis, range of factors, and the target performance measures.