Level-of-Service Determination Before the implementation of any developed signal phasing and timing plan, the level of service should be determined to assess whether the intersection will operate at an acceptable level under this plan. As previously mentioned, the service measure (the performance measure by which level of service is assessed) for signalized intersections is delay. In previous examples, we calculated the delay for a specific lane group, but now we must do this for all lane groups and then aggregate the delay values to arrive at an overall intersection delay measure and corresponding level of service.
The first step is to aggregate the delays of all lane groups for an approach, and then repeat the procedure for each approach of the intersection. This will result in approach-specific delays and levels of service. The aggregated lane group delay for each approach is given by
i i i
where dA = average delay per vehicle for approach A in seconds, di = average delay per vehicle for lane group i (on approach A) in seconds, and vi = analysis flow rate for lane group i in veh/h.
Once all the approach delays have been calculated, they can be aggregated to arrive at the overall intersection delay.