Metroplex, the five-light left turn signal head is used in a different manner than standard signals of this type. The left turn signal head operates independently from the signals for straight through traffic. This allows permissive turning even when straight through traffic is shown a red light, avoiding yellow trap. Louvers are fitted over the green and yellow balls of the left turn signal head to prevent driver confusion. The left turn signal head is also accompanied by a sign indicating its special use. In this configuration, the left-turn signal will display circular green from the leading protected left turn phase until the lagging permissive left turn phase, but the green arrow will only be displayed during the leading protected left-turn phase. During the lagging permissive left-turn phase, it is assumed that opposing traffic has both a permissive left turn phase and a straight-through green light. This can also be used in the opposite configuration, with leading permissive and lagging protected left-turn phases. Dallas phasing gives traffic engineers more flexibility with the leading and lagging protected left turn phase configurations allowing for better coordination between signals. There are also yellow and green arrows on Dallas phasing signals, permitting exclusive protected left-turn phases as well as protected/permissive left-turn phases. The 2009 Manual of Uniform Traffic Control Devices prohibits this display for new installations in favor of the flashing-yellow-arrow left-turn signal, which accommodates both permissive and protected left turns. Older installations are allowed to stay until they are replaced. Arlington phasing Arlington County, Virginia used the classic five-light "doghouse" (1971) with steady green and yellow arrows on the left, and green and yellow balls on the right, topped by a red ball. The light sequence started with a green arrow, proceeding to a left arrow, then a green ball, yellow ball, and finishing with a red ball. The signal was accompanied by a sign stating that left turns (against oncoming traffic) were required to yield on a green ball. These were later replaced by four-light signals that included a flashing yellow arrow. Flashing red ball, yellow ball, or red arrow Michigan uses a 3-lamp traffic signal, with a red ball, yellow arrow, and green arrow; during the permissive turn, the red ball flashes. A flashing red ball signal on a "protected" left turn traffic signal indicates that left turning traffic may, after a full stop, complete their turn if and only if