Opposed right-turning vehicles and gap acceptance

Right-turning vehicles present particular problems at signal-controlled intersections. On a signal approach, right-turn vehicles may be given an exclusive right-turn lane or they may be mixed with straight ahead vehicles. If vehicles do not have to give way, that is, the flow is unopposed, then the maximum discharge or saturation flow can be calculated using the relationships given in Chapter 33. When the flow is opposed and the right-turn vehicles are mixed with straight ahead vehicles then once again the relationships given in Chapter 33 can be used to calculate the saturation flow. If however the right-turn flow is opposed and is not mixed with straight ahead vehicles then the following simplified approach to the calculation of the right-turn discharge can be used. In this case some right-turn vehicles are able to turn through gaps in the opposing straight ahead flow and the remainder must turn in an early cut-off intergreen period at the end of the green period.