The 'Intermediate Sight Distance' (ISD) in India (IRC:66) is equal to:
Choose the correct answer
Same as OSD (overtaking sight distance)
ISD = 2 × SSD — provides limited overtaking opportunity where full OSD is uneconomical (e.g., hilly terrain)
Equal to SSD ÷ 2
ISD = 3× SSD
Correct Answer
B. ISD = 2 × SSD — provides limited overtaking opportunity where full OSD is uneconomical (e.g., hilly terrain)
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ISD (Intermediate Sight Distance) = 2 × SSD (Stopping Sight Distance). Concept: driver can see oncoming vehicle (both moving) and stop before collision if needed. Provides limited overtaking opportunity. OSD (Overtaking Sight Distance) = safe distance to overtake slow vehicle — much longer (6–10× SSD). Values: at 80 km/h: SSD ≈ 120 m; ISD ≈ 240 m; OSD ≈ 470 m (IRC:66). Provided on: ghat roads, military roads where full OSD uneconomical.
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