Traffic flow terminology: The maximum number of vehicles that can pass a given point on a lane in one hour without causing unreasonable delay is called the…

Introduction / Context:
Roadway capacity concepts differentiate between theoretical maxima and what is realistically achievable in daily operations. Designers use these concepts to evaluate level of service and to plan lane additions, intersections, and control strategies.

Given Data / Assumptions:

• An hourly rate of vehicles passing a point is being considered.
• “Without unreasonable delay” implies real-world operating conditions rather than idealized ones.
• Lane-level analysis is intended (single lane in one direction).

Concept / Approach:

Basic capacity is the theoretical maximum under ideal conditions (perfect drivers, vehicles, weather, alignment, and control). Practical capacity (sometimes called possible or service capacity) is lower and reflects the highest flow rate that can be sustained with acceptable operational comfort and without excessive delay or breakdown of flow.

Step-by-Step Solution:

Verification / Alternative check:

When plotted on a speed–flow curve, practical capacity corresponds to the peak of serviceable throughput before speeds drop sharply and delays escalate, unlike basic capacity which assumes ideal, rarely attainable conditions.

Why Other Options Are Wrong:

• Traffic density: vehicles per unit length at an instant, not a throughput rate.
• Basic capacity: ignores real-world frictions; does not mention delay acceptability.
• Probable capacity: non-standard term; ambiguous.

Common Pitfalls:

• Confusing flow rate (veh/h) with density (veh/km) or speed (km/h).
• Assuming the maximum theoretical number equals acceptable operations; it often does not.

Final Answer:

Practical capacity of the lane.