How is the term 'capacity' distinguished from 'saturation flow rate'?

• A. Capacity includes lost time; saturation does not
• B. Capacity is a theoretical maximum; saturation is practical
• C. Capacity applies to streets; saturation applies to signals
• D. Capacity considers only peak hours; saturation is for all hours

Answer: (B)

The distinction between 'capacity' and 'saturation flow rate' is rooted in their definitions and applications in traffic engineering. Capacity refers to the maximum amount of traffic that can be accommodated on a roadway or at an intersection during a specific time period under prevailing conditions. It represents a theoretical maximum, taking into consideration various factors like traffic demand, roadway conditions, and the ability to clear vehicles effectively.

On the other hand, the saturation flow rate pertains to the physical characteristics and performance of the roadway or intersection during high-demand situations. It reflects the flow of vehicles that can pass through a point when traffic is at its peak, but unlike capacity, it is based on observed conditions rather than theoretical limits. Saturation flow rate is often a practical measure, representing the actual number of vehicles that can traverse a signal-controlled intersection once the signal turns green and the flow is uninterrupted.

This understanding of the two concepts is crucial for traffic analysis, as it helps engineers evaluate potential improvements and adjustments in traffic systems. When differentiating between them, it is clear that capacity is a theoretical maximum reflective of ideal conditions, while saturation flow rate deals with what can realistically occur during peak conditions.