21-by-9-inch (525 mm × 225 mm) By-pass plate  from the 1971 <a href="https://en.wikipedia.org/wiki/Manual_for_Uniform_Traffic_Control_Devices" class="extiw" title="w:Manual for Uniform Traffic Control Devices">Manual for Uniform Traffic Control Devices</a>
<p>Design: <a href="https://en.wikipedia.org/wiki/Federal_Highway_Administration" class="extiw" title="w:Federal Highway Administration">Federal Highway Administration</a>
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This image: <a href="//commons.wikimedia.org/wiki/User:Fredddie" title="User:Fredddie">Fredddie</a>
2022-12-24
1961 MUTCD