Stopping sight distance is increased with

Question

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The correct answer is Option B: decrease in brake efficiency. Stopping Sight Distance (SSD) is the minimum distance required for a driver to see an obstruction and stop the vehicle safely. Since SSD is inversely proportional to the braking efficiency and frictional resistance, any decrease in brake efficiency necessitates a longer distance to dissipate the vehicle's kinetic energy.

Step-by-Step Solution & Concepts:
Stopping Sight Distance (SSD) is the minimum distance required for a driver to see an obstruction and stop the vehicle safely. Since SSD is inversely proportional to the braking efficiency and frictional resistance, any decrease in brake efficiency necessitates a longer distance to dissipate the vehicle's kinetic energy.

Working Principle: The total SSD is the sum of Lag Distance ($d_{lag} = v \cdot t$) and Braking Distance ($d_{braking} = \frac{v^2}{2g(f \pm s)}$). If brake efficiency ($\eta$) decreases, the effective longitudinal friction coefficient ($f_{effective} = f \cdot \eta$) reduces. A smaller denominator in the braking distance formula leads to a higher overall SSD value.

Key Formulas: $SSD = v \cdot t + \frac{v^2}{2g(f \cdot \eta \pm s)}$ — where $v$ is velocity, $t$ is reaction time, $f$ is friction, $\eta$ is efficiency, and $s$ is gradient.

Key Points: SSD consists of Reaction Distance and Braking Distance.; Reaction distance depends solely on speed and reaction time.; Braking distance is highly sensitive to pavement surface condition and mechanical brake condition.; A decrease in brake efficiency ($\eta$) directly increases the braking distance component.

Advantages: Ensures safety by accounting for worst-case mechanical conditions.; Provides a design basis for horizontal and vertical curve lengths.

Applications: Highway geometry design; Intersection sight distance evaluation; Pavement marking and signage placement

Additional Info: Standard reaction time for Indian highway design is typically taken as 2.5 seconds.. Option A increases safety/reduces SSD, Option C increases friction which reduces SSD, Option D reduces reaction distance which reduces total SSD.

Answer: B is correct — A decrease in brake efficiency reduces the negative acceleration (deceleration) capability of the vehicle, thereby increasing the distance required to bring it to a complete stop.

Exam Tip: Remember that SSD is additive; any factor that decreases the denominator of the Braking Distance component ($2g\eta f$) will result in an increase in the total SSD.

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Option A: increase in brake efficiency

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Option C: increase in frictional resistance of pavement

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Option D: decrease in brake reaction time

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