Signal Phasing Recall
Select Signal Phasing Recall that a timing stage consists of the time during which the same combination of movements, across one or more phases, are moving simultaneously and that the sum of the timing stage lengths is equal to the cycle length. The most basic traffic signal cycle is made up of two timing stages. In this case, timing stage 1 accommodates the movement of all the eastbound and westbound vehicles, and timing stage 2 accommodates the movement of all the northbound and southbound vehicles. These timing stages will alternate during the continuous operation of the signal. This timing-stage scheme, however, could prove to be very inefficient if one or more of the approaches includes a high left- turn volume.
Given that each approach consists of one lane, vehicles will be delayed behind a left-turning vehicle waiting for a gap in the opposing traffic stream. If the high volume of left turns is present on both the northbound and southbound approaches, for example, each of these approaches could be given a separate timing stage consisting of the left-turn phases. This would be more efficient because left-turning vehicles on these two approaches would not have to wait for gaps in the opposing traffic stream, thus greatly reducing delays for all vehicles. This would result in a three-timing-stage operation. When phases for movements on opposing approaches are run in a separate timing stage, as in this case, it is referred to as split phasing.
