Several complaints recently have been sent to the LA city office regarding the increasing incidence of congestion on the city’s streets. The complaints attribute the cause of these traffic tie-ups to...

Several complaints recently have been sent to the LA city office regarding the increasing incidence of congestion on the city’s streets. The complaints attribute the cause of these traffic tie-ups to a lack of synchronization of the traffic lights. The lights are controlled by a main computer system, and adjusting this program is costly. Therefore, the city is reluctant to change the situation unless a clear need is shown. During the past three months, the office initiated a study and collected 226 data each month at major intersections and identify the # of congestion incidents. The congestion data is shown below.

What is the upper control limit, for a 4-sigma quality standard, based on the above data?