Traffic control devices — STOP sign shape as per IRC:67-2001 According to Indian Roads Congress standard IRC:67-2001, what is the standard geometric shape of the STOP regulatory sign used on Indian highways and urban roads?

Introduction / Context:
Traffic signs use standardized shapes and colors so drivers can recognize them quickly even at a distance or when partially obscured. The STOP sign is one of the most critical regulatory signs, and its shape is harmonized internationally to avoid confusion across jurisdictions.

Given Data / Assumptions:

• Reference standard: IRC:67-2001 (Code of Practice for Road Signs).
• We focus on the geometric shape only, not color or lettering.
• The sign conveys the legal requirement to come to a complete stop and proceed when safe.

Concept / Approach:
The STOP sign is octagonal, a unique shape among common road signs. This uniqueness prevents misinterpretation from the back side and remains identifiable when snow, dirt, or vegetation partially obscures the sign. The octagon also differentiates STOP from other regulatory and warning signs, which are typically circular, triangular, rectangular, or diamond-shaped.

Step-by-Step Solution:
Recall standard shapes: circular (speed limits), triangular (give way/yield in some systems; warning in IRC), rectangular (informational/guide), diamond (warning, in some standards), and octagonal (STOP).Match STOP to the unique octagon per IRC:67.Select “Octagonal”.

Verification / Alternative check:
Field signage and official plates show the distinctive eight-sided profile, typically with red background and white legend “STOP”.

Why Other Options Are Wrong:
Circular, triangular, rectangular, diamond: Used for other sign categories; none is used for STOP in IRC:67.

Common Pitfalls:

• Confusing yield/give-way triangle with STOP; yield is triangular, STOP is octagonal.
• Assuming shape conventions from a different country override IRC standards.

Final Answer:
Octagonal