ABC Beverage Drive-Thru
ABC Beverage Drive-Thru, Inc., operates a chain of beverage supply stores in the Midwest (where the sale of alcohol is not done through state controlled stores, as it is in NC). Each store has a single service lane; cars enter at one end of the store and exit at the other end. Customers buy soft drinks, snacks, and party supplies without getting out of their cars. When a new customer arrives at the store, s/he waits until the preceding customer leaves, the pulls forward to be waited on.
Typically, three employees are scheduled for peak hours: two clerks take and fill orders while a third acts as cashier and supervisor. A new store design based on computerized order-taking and payment with special equipment to facilitate pulling the items is being considered. It is expected that the new design will require only one clerk to operate the store. They have asked you to simulate the new design before deciding whether or not to try it by building a new store.
All ABC stores are located near major shopping centers. During peak hours (late afternoon and evening) customers arrive steadily. The time-between-arrivals follows an exponential distribution with a mean of 6. Customer service, using the new design, is estimated to follow the empirical distribution in Table 1:
Service Time (minutes) / Probability2 / 0.24
3 / 0.20
4 / 0.15
5 / 0.14
6 / 0.12
7 / 0.08
8 / 0.05
9 / 0.02
Total: / 1.00
Table 1: Empirical Distribution for Service Times
Two options are being considered: having two clerks in the store (to reduce service times) or building a larger store to allow two cars to be serviced at once (called a two channel system). Either of these options will require two clerks, but the service times for the two channel system will be the same as above. Having two clerks on the one-channel system will reduce service times to the empirical distribution shown in Table 2:
Service Time (minutes) / Probability1 / 0.20
2 / 0.35
3 / 0.30
4 / 0.10
5 / 0.05
Table 2: Empirical Distribution for Service Times for Two-Channel System
Customer wait-time is major issue for your company. The corporate goal is to have average wait time be less than 1.5 minutes. If wait time is greater than 6 minutes, then there is 30% chance the customer while drive off without making a purchase. If the wait time exceeds 10 minutes, there is a 90% chance the customer will drive off.
The accompanying spreadsheet contains the set up for simulating the first design (one-channel, one clerk). You must finish that simulation by continuing it for 1,000 customers, and then develop similar simulations for the one-channel, two clerks design, and the two-channel design.
Instructions for writing up this case will be posted tomorrow, along with a statement of deadlines and requirements for all students.