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Road capacity definition and types

Short answer

Capacity is the maximum vehicles or PCUs passing a point in one hour under prevailing roadway, traffic, and control conditions. Types are basic (ideal conditions), possible (prevailing conditions), and practical or design capacity, about 75-80 percent of possible capacity at a chosen level of service.

Define the capacity of a road and list out its types.

The capacity of a road is the maximum number of vehicles (or PCUs) that can pass a given point or section of a lane or road in one direction (or both directions on a two-lane road) during a given time period (normally one hour) under the prevailing roadway, traffic and control conditions (HCM definition; IRC:106 for urban roads).

Types of capacity:

  1. Basic capacity: the maximum number of passenger cars that can pass in a lane under ideal (best possible) roadway and traffic conditions.
  2. Possible capacity: the maximum number that can pass under the actual (prevailing) roadway and traffic conditions, i.e. after adjusting the basic capacity for lane width, shoulders, gradient, heavy vehicles, etc.
  3. Practical capacity (design capacity): the maximum number that can pass without unreasonable delay or restriction to the drivers' freedom to manoeuvre, at the chosen level of service. It is about 75-80 percent of the possible capacity (design service volume at LOS C for urban roads in IRC:106, and at LOS B for rural roads in IRC:64).

✓ Answer checked by Claude Opus 5.5 (high effort)

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