Traffic engineering – factors governing the capacity of a single-lane highway For a single traffic lane, the practical traffic carrying capacity depends primarily on which of the following field factors?

Introduction / Context:
Single-lane capacity is not a fixed number; it varies with roadway environment, traffic composition, control features, and pavement condition. Understanding these influences helps planners estimate realistic flows and set safe, efficient operating policies.

Given Data / Assumptions:

• One traffic lane in one direction.
• Mixed traffic typical of highways (cars, buses, trucks, two-wheelers).
• Conventional control at intersections and level crossings.
• Dry weather, open alignment unless otherwise stated.

Concept / Approach:
Capacity is governed by headways (time gaps) between vehicles. Anything that increases headway reduces capacity. Heavy vehicles, frequent stops, rough textures, or poor friction increase spacing and lower discharge flow.

Step-by-Step Solution:

Verification / Alternative check:
Fundamental diagrams link speed–flow–density; any factor that lowers desired speed or increases spacing shifts the curve downward, confirming reduced capacity.

Why Other Options Are Wrong:
Each single factor (options A–D) matters, but capacity is the combined outcome; hence only All the above captures the complete picture.

Common Pitfalls:
Assuming only lane width controls capacity; ignoring the strong effect of heavy vehicle percentage and control devices.

Final Answer:
All the above