Tractive effort on upgrades: For computing tractive force on an asphalt road upgrade, the most probable coefficient of traction (rolling) resistance μ is typically assumed as

Introduction / Context:
Estimating tractive effort is essential for checking vehicle performance on grades, sizing engines, and verifying hill road feasibility. The force must overcome rolling (traction) resistance, grade resistance, and any aerodynamic and acceleration components. A representative coefficient for rolling resistance is needed for asphalt surfaces.

Given Data / Assumptions:

• Pavement: bituminous (asphalt), in good condition.
• Speed: moderate highway speeds; tires properly inflated.
• Objective: pick a typical coefficient μ for rolling (traction) resistance.

Concept / Approach:

For paved, smooth asphalt, μ for rolling resistance commonly lies around 0.015 to 0.025. Design calculations often round to 0.02 as a representative value for normal conditions, balancing conservatism and realism. On rougher surfaces or gravel, μ is larger; on concrete in excellent condition, it may be slightly lower.

Step-by-Step Solution:

Verification / Alternative check:

Vehicle performance handbooks and highway engineering texts list μ values near 0.02 for smooth, paved asphalt under normal conditions. Sensitivity checks with μ = 0.015 and μ = 0.025 confirm limited variation for moderate grades.

Why Other Options Are Wrong:

• 0.01: unusually low for typical asphalt; optimistic.
• 0.03–0.05: more suited to rough, gravel, or soft surfaces; pessimistic for good asphalt.

Common Pitfalls:

• Confusing rolling resistance with coefficient of lateral friction used in superelevation design.
• Ignoring speed and tire effects when refining μ for specific projects.

Final Answer:

0.02.