Practice question · Multiple choice
A hospital plans its emergency department at 98% average utilisation and waiting times explode. Why does the last few percent cost so much?
Hints
- Patients do not arrive on a timetable. Ask what absorbs a burst when the system is already full.
- Sketch waiting time against utilisation. What is the shape near 100%?
Show the answer
D. Because queue length grows without bound as utilisation nears 1
Why
Waiting time rises roughly as 1/(1−ρ), so it is nearly flat until it turns vertical, variability needs slack to absorb it and 98% leaves none. High utilisation looks efficient on a spreadsheet and is the reason motorways jam at exactly the moment they are being used best.
Practise Operations Management
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