The sign is available to be added as a plaque in conjunction with the pre-existing R4-11 (Bicycles) MAY USE FULL LANE (“BMUFL”), which made it’s debut in the 2009 edition of the MUTCD, and was finally added to Arizona’s MOAS in June 2013.
Most lanes in Arizona, and elsewhere for that matter, are designed to accommodate only the width of one vehicle, not a
bicycle and a vehicle side-by-side safely. In this situation, bicyclists need not (legally) ride as far to the right as practicable, but rather are instructed to ride near the center of the lane as best safe practice, this position will make the bicyclist more visible to other motorists, giving them more time to avoid abrupt, unsafe movements.
Below is a typical laned arterial road configuration, this happens to be in Tempe… The lanes are too narrow to share safely side-by-side. Non-standard signs, such as the “Share the Road” should be replaced —
As noted in Table 9B-1. Bicycle Facility Sign and Plaque Minimum Sizes of the MUTCD the minimum size of this sign is 30″ wide.