Braking distance on level pavement at 30 km/h (effective brakes) On a level highway with effective brakes and typical dry-pavement friction, a vehicle travelling at 30 km/h will come to a stop in approximately:

Introduction / Context:Braking distance depends primarily on initial speed and available longitudinal friction. For quick checks, standard values are tabulated for typical dry conditions and effective brakes.

Given Data / Assumptions:

• Initial speed V = 30 km/h = 8.33 m/s.
• Level road; no grade effects.
• Effective brakes on dry pavement (typical design friction in the range 0.3–0.4 used for conservative SSD in basic tables).

Concept / Approach:Using uniform deceleration, braking distance s = v^2 / (2 * g * f). Adopting f ≈ 0.3–0.35 gives conservative distances commonly cited in design aids for low speeds.

Step-by-Step Solution:

Verification / Alternative check:Using highway units: s ≈ V^2 / (254 * f) = 30^2 / (254 * 0.30) ≈ 900 / 76.2 ≈ 11.8 m, consistent with the above.

Why Other Options Are Wrong:10 m is feasible but less conservative; 15 m and 18 m are excessive for the assumed conditions.

Common Pitfalls:Forgetting to include reaction distance in full SSD; using wet or icy friction without adjusting the estimate.

Final Answer:12 metres