10 M.P.H.

Additional Details

MUTCD Section 2C.46 Advisory Speed Plaque (W13-1)
Option: The Advisory Speed (W13-1) plaque (see Figure 2C-5) may be used to supplement any warning sign to indicate the advisory speed for a condition.

Standard: The Advisory Speed plaque shall be used where an engineering study indicates a need to advise road users of the advisory speed for a condition.
If used, the Advisory Speed plaque shall carry the message XX km/h (XX MPH). The speed shown shall be a multiple of 10 km/h or 5 mph.
Except in emergencies or when the condition is temporary, an Advisory Speed plaque shall not be installed until the advisory speed has been determined by an engineering study.

Guidance: Because changes in conditions, such as roadway geometrics, surface characteristics, or sight distance, might affect the advisory speed, each location should be periodically evaluated and the Advisory Speed plaque changed if necessary.

Option: The advisory speed may be the 85th-percentile speed of free-flowing traffic, the speed corresponding to a 16-degree ball bank indicator reading, or the speed otherwise determined by an engineering study because of unusual circumstances.

Support: A 10-degree ball-bank indicator reading, formerly used in determining advisory speeds, is based on research from the 1930s. In modern vehicles, the 85th-percentile speed on curves approximates a 16-degree reading. This is the speed at which most drivers' judgment recognizes incipient instability along a ramp or curve.