MUTCD R2-1: Speed Limit Sign

The R2-1 sign is covered in Section 2B.21 of the Manual on Uniform Traffic Control Devices, 11th Edition. Below are the provisions from that section that describe when the sign is used and how it is placed.

What it means and when it is used

• Standard · Required (shall)
  Speed zones (other than statutory speed limits) shall only be established on the basis of an engineering study that has been performed in accordance with traffic engineering practices. The engineering study shall consider the roadway context.
• Guidance · Recommended (should)
  Among the factors that should be considered when conducting an engineering study for establishing or reevaluating speed limits within speed zones are the following: A. Roadway environment (such as roadside development, number and frequency of driveways and access points, and land use), functional classification, public transit volume and location or frequency of stops, parking practices, and pedestrian and bicycle…

Placement and mounting

• Guidance · Recommended (should)
  When the 85th-percentile speed is appreciably greater than the posted speed limit, and the roadway context does not support setting a higher speed limit, the engineering study should consider whether changes to geometric features, enforcement, and/or other speed-reduction countermeasures might improve compliance with the posted speed limit. A similar approach should be used if the results of past speed studies…
• Guidance · Recommended (should)
  Sect. 2B.2110 On a freeway, expressway, or rural highway (outside urbanized locations or conditions), the speed limit that is posted within a speed zone should be within 5 mph of the 85th-percentile speed of free-flowing motor-vehicle traffic under the following conditions: A. All factors described in Paragraph 7 of this Section have been considered and determined to be non-mitigating, and B. The measures described…
• Standard · Required (shall)
  Speed Limit (R2-1) signs, indicating speed limits for which posting is required by law, shall be located at the points of change from one speed limit to another.

Where to read the rest

• Full text: MUTCD Section 2B.21: Speed Limit Sign
• Minimum sign sizes by roadway type are in the size section for this chapter: Section 2B.03
• Mounting height, lateral offset and retroreflectivity for any sign: MUTCD sign placement guide