Highway braking test – estimating skid resistance (friction coefficient) A vehicle travels at 36 km/h and, during a braking test on level pavement, comes to rest in a measured braking distance of 8.0 m. What is the average skid resistance (coefficient of friction) for the test?

Introduction / Context:
Estimating pavement skid resistance from a controlled stop is a staple calculation in highway engineering. It links the observed stopping distance with speed through basic kinematics and allows us to infer the average friction coefficient between tires and road.

Given Data / Assumptions:

• Initial speed V = 36 km/h.
• Measured stopping distance s = 8.0 m.
• Level road (grade = 0), uniform braking.
• Standard gravitational acceleration g ≈ 9.81 m/s^2.

Concept / Approach:
For uniform deceleration on level ground, the stopping distance under friction-controlled braking is s = v^2 / (2 * g * f), where v is speed in m/s and f is the average friction coefficient. Rearranging gives f = v^2 / (2 * g * s).

Step-by-Step Solution:

Verification / Alternative check:
Using the km/h form with constant 254: braking distance s ≈ V^2 / (254 * f) ⇒ f ≈ V^2 / (254 * s) = 36^2 / (254 * 8) ≈ 1296 / 2032 ≈ 0.64, matching the previous result.

Why Other Options Are Wrong:
6.25 and 0.16 are far from realistic friction values for dry pavement. “None of these” is incorrect because 0.64 is a valid, typical dry-road result.

Common Pitfalls:
Forgetting to convert km/h to m/s; using g = 10 without checking sensitivity; neglecting grade or brake efficiency when present in other problems.

Final Answer:
0.64