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INV is close to INVmax= 5 cars. Hence, a better estimate of the actual peak throughputisλ= 5/167.9 cars per second,assumingthat CT = 167.9 seconds is accurate for the 90-minute lunch rush. (The original QSR study actually indicates that this is CT for the timewindows 11am-2:30pm and 4pm-7pm).A first-pass at a corrected estimate is the following:(a) 5,400 seconds in 90 minutes(b) Assuming INV = 5 cars when CT = 167.9 seconds, this implies 5,400(5/167.9) = 160cars served per restaurant during that period at current service speed.1
(c) 77.9 seconds, is what McD’s must shave off its average drive-through time to hit its90-second target.(d) At CT = 90 seconds, they could serviceat most5,400(5/90) = 300 cars in that periodon average, assuming INV = INVmax= 5 cars at this new CT. This would be theircapacity (recall the ovens at Varsity Subs).So they could serviceat mostan extra300-160 = 140 cars, combining the result with part 2.(e) Assuming $5 revenue per car, this yields ($5)(140) = $700 extra revenue per day foreach restaurant.(f) Assuming 300 good drive-through days per year, this amounts to ($700)(300) = $210,000in additional peak period revenue earned per restaurant annually.(g) Across 13,673 locations, this totals $2.87 billion, or about 15% of their current annualrevenues of around $20 billion.In general, all the numbers (except 77.9 and 5,400) stated in the figure must be multipliedby INV≈INVmax= 5.