Flashing Yellow Arrow

For protected-permissive left turn phasing, UDOT uses either a Flashing Yellow Arrow (FYA) or a five-section (a.k.a., “doghouse”) signal head. FYA signals are becoming more common, largely due to the flexibility that they provide, including the ability to switch between protected-only and protected-permissive based on time of day or traffic conditions (this can be determined through field observations or reviewing the signal controller logic). While both signal head types operate similarly in protected-permissive mode, there is a key difference that needs to be included in any traffic model. This difference is that the permissive left turn phase is tied to a different phase for each signal head type as shown in the table below. For five-section heads the permissive phase is tied to the adjacent through movement and for FYA the permissive phase is tied to the opposing through movement. 

This means that there are times during the signal cycle when a FYA signal head will allow a permissive left turn even though the light is red for the adjacent through lane(s). This occurs when the opposing left turn phase is either skipped or runs longer than that of the subject left turn. During this time the FYA provides additional time for permissive left turns, reducing the delay for the left turn movement. An illustration of how protected-permissive phasing is coded in Vissim for each signal type is shown in Figure 29 and Figure 30 below.