inserted between the yellow left turn arrow and green left turn arrow. When the phase is active, the yellow arrow will flash. Drivers turning left or making a U-turn must be cautious and yield to both oncoming vehicles and to pedestrians. The US MUTCD includes this meaning of the flashing yellow arrow, but though in 2008 the state had planned to require all new signals to have flashing yellow arrows, the 2011 Michigan MUTCD prohibits the flashing yellow arrow in favor of a flashing red arrow. The benefit of its introduction is that traffic engineers have a wider range of options to handle variable traffic volumes. According to the Minnesota Department for Transport, the flashing yellow arrow reduces delays and enhances safety. A research report from the National Cooperative Highway Research Program in the US found that it improves safety compared with a standard circular green signal. The flashing yellow arrow has an important safety advantage because it can be shown while the through signals on the same approach are red. The flashing yellow arrow is also meant to prevent yellow trap, which occurs when the circular signal turns yellow, and then red, while oncoming traffic still has a circular green. Though Dallas Phasing resolved the yellow trap issue, flashing yellow arrow has been deemed less confusing than a louvered green ball, and problems might ensue if the left turn signal comes out of adjustment and its indications are visible to through traffic In the United States, the flashing yellow arrow is not allowed where left turns and other traffic share the same lane. The circular green is still allowed as a permissive left turn display, but has new restrictions: It may not be placed over or in front of the left turn lane in new installations. Any yellow trap caused by a circular green must be eliminated or warned with a sign. If one lane is shared by left turning and straight ahead traffic, the left turn movement (protected or permissive) and the straight ahead movement must begin together and must end together at the same time in the signal cycle. In this case, a green left turn arrow may not be shown with a circular red, and a red left turn arrow may not be shown with a circular green or a straight ahead green arrow. Flashing green In Canada, there is disagreement between the provinces over the