Self-Service Checkout. Will More Lines Improve Customer Throughput? Kevin W. Lewelling Professor Ernesto Butierrez-Miravete DSES – 6620 Simulation Modeling And Analysis May 1, 2002

Unlimited Full-Service, Unlimited Full-Service 12 Items or Less Enter Exit Enter Exit Customer Service Area Carriage Area Carriage Area 12 or Less Self-Service Current Store Checkout Area Layout

6 ½ ft 7 ft Unlimited Standard Width Unlimited Handicap Width 12 or less Handicap Width 12 or less Standard Width Full Service Checkout Line Configurations Arrival QueueCheckout Associate Service Location Exit Feeder Conveyor Gathering Area Bagging Associate 5 ½ ft Unlimited or 12 or less Arrival Queue Service Location Exit Transfer Conveyors Gathering Area Self-Service Checkout Line Configuration

Problem Solution Approach Understand current customer throughput Collect data Inter-arrival times Service times Checkout line configurations Reduce data for analytical representations Generate simulation models Run simulation models Full-service unlimited Full-service 12 items-or-less Self-service unlimited Self-service 12 items-or-less Full-service unlimited Full-service 12 items-or-less Self-service unlimited Self-service 12 items-or-less Evaluate Line Combinations

Reduced Input Data Full Service – UnlimitedWeibull (1.36, 2.71)Beta (17.6, 14.7, 0, 2.92) Full Service – 12 Items-or-LessExponential (0.888)Lognormal (0.0442, 0.422) Self-Service – UnlimitedGamma (1.21, 2.74)Lognormal (1.06, 0.795) Self-Service - 12 Items-or-LessWeibull (1.01, 2.1)Erlang (3, 0.873) Line TypesInter-arrival TimesService Times Simulation Runs 20 Iterations each 2 hour warm-up 4 hour run time

Simulation Results – Customer Throughput per hour Full Service – Unlimited Self-Service – Unlimited Full Service – 12 Items-or-Less Self-Service - 12 Items-or-Less Line TypesAverageStd. Dev.Min.Max. Simulation Results – Number of Customers in the Arrival Queues Full Service – Unlimited Self-Service – Unlimited Full Service – 12 Items-or-Less Self-Service - 12 Items-or-Less Line TypesAverageStd. Dev.Min.Max.

Optimization Procedure Data from Simulation analysis 16 Given Solved For Sequentially Incremented

Number of Checkout Lines Total Customer Throughput Total Customer Throughput for Given Checkout Line Configurations Fewer Self-Service Checkout Lines Unlimited Item Checkout Lines

Total Customer Throughput Fewer Self-Service Checkout Lines Total Customer Throughput Unlimited Item Checkout Lines Enlarged Curve Current 7 Self- Service

Number of Checkout Lines Total Customer Throughput Total Customer Throughput for Given Checkout Line Configurations 12 Items-or-less Checkout Lines Fewer Self-Service Checkout Lines Current

Conclusions / Recommendations Self-service lines provide no additional throughput A cost analysis should be performed to determine the real solution A hybrid checkout system would solve all of their problems