When a police officer holds one arm out horizontally, traffic moving parallel to that arm is given the same meaning as a green light.

Explanation

An arm held out horizontally means that traffic running parallel to the arm may proceed, exactly as with a green light. If the officer lowers the arm, the front of the officer's body — not the arm — is what decides which directions count as "parallel".

Guides that explain this

• Japanese Signs That Mean the Opposite of What You Assume: Crosswind, End of Restriction, Minimum Speed
• Japanese Road Signs on the Written Test: The 5 Types Explained

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