The lenses on a signal face should be arranged in a vertical or horizontal straight line with each signal face having at least three, four, or five lenses. The lenses shall be red, yellow, or green and give ball or arrow-type indications. Five lenses arranged vertically have the ball and arrow green and yellow indications side-by-side, with a centered red ball at the top.
The figure on the left shows the typical position and arrangements of separate signal faces with flashing yellow arrow for permissive only mode left turns. The other figure shows the typical position and arrangements of shared signal faces for protected/permissive mode left turns. The flashing yellow arrow is another option to display the signal for protected-permitted left-turning phases, or a permitted left-turn in the absence of a protected phase. With this, a flashing yellow indication is used when left-turns are permitted. An advantage of this is that it is possible to use protected only phasing during certain hours of the day. Refer the MUTCD Chapter 4D for additional scenarios.