Chapter 12 Managing Waiting Lines McGraw-Hill/Irwin Service Management: Operations, Strategy, and Information Technology, 6e Copyright © 2008 by The McGraw-Hill.

Chapter 12Managing Waiting Lines

McGraw-Hill/IrwinService Management: Operations, Strategy, and Information Technology, 6e

Copyright © 2008 by The McGraw-Hill Companies, Inc. All Rights Reserved.

Lines and Waiting

“Every day I get in the queue, that waits for the bus that takes me to you …”

Pete Townshend, Magic Bus

12-2

Learning Objectives Describe the economies of waiting lines using

examples. Describe how queues form. Apply Maister’s two “laws of service.” Describe the four psychology of waiting

components and suggest strategies to deal with each.

Describe the four principles of waiting line management.

Describe the essential features of a queuing system.

Describe the relationship between a negative exponential distribution of time between arrivals and a Poisson distribution of arrival rates.

12-3

Where the Time Goes

In a life time, the average person will spend:

SIX MONTHS Waiting at stoplights

EIGHT MONTHS Opening junk mail

ONE YEAR Looking for misplaced 0bjects TWO YEARS Reading E-mail FOUR YEARS Doing housework FIVE YEARS Waiting in line SIX YEARS Eating

12-4

Cultural Attitudes “Americans hate to wait. So business is

trying a trick or two to make lines seem shorter…” The New York Times, September 25, 1988

“An Englishman, even when he is by himself, will form an orderly queue of one…” George Mikes, “How to be an Alien”

“In the Soviet Union, waiting lines were used as a rationing device…” Hedrick Smith, “The Russians”

12-6

Waiting Realities

Inevitability of Waiting: Waiting results from variations in arrival rates and service rates

Economics of Waiting: High utilization purchased at the price of customer waiting. Make waiting productive (salad bar) or profitable (drinking bar).

12-8

Laws of Service Maister’s First Law:

Customers compare expectations with perceptions.

Maister’s Second Law:Is hard to play catch-up ball.

Skinner’s Law:The other line always moves faster.

Jenkin’s Corollary:However, when you switch to another other line, the line you left moves faster.

12-10

Remember Me I am the person who goes into a restaurant, sits

down, and patiently waits while the wait-staff does everything but take my order.

I am the person that waits in line for the clerk to finish chatting with his buddy.

I am the one who never comes back and it amuses me to see money spent to get me back.

I was there in the first place, all you had to do was show me some courtesy and service.

The Customer

12-11

Psychology of Waiting

That Old Empty Feeling: Unoccupied time goes slowly

A Foot in the Door: Pre-service waits seem longer that in-service waits

The Light at the End of the Tunnel: Reduce anxiety with attention

Excuse Me, But I Was First: Social justice with FCFS queue discipline

They Also Serve, Who Sit and Wait: Avoids idle service capacity

12-12

Approaches to Controlling Customer Waiting

Animate: Disneyland distractions, elevator mirror, recorded music

Discriminate: Avis frequent renter treatment (out of sight)

Automate: Use computer scripts to address 75% of questions

Obfuscate: Disneyland staged waits (e.g. House of Horrors)

12-13

Essential Features of Queuing Systems

DepartureQueue

discipline

Arrival process

Queueconfiguration

Serviceprocess

Renege

Balk

Callingpopulation

No futureneed for service

12-18

Arrival Process

Static Dynamic

AppointmentsPriceAccept/Reject BalkingReneging

Randomarrivals withconstant rate

Random arrivalrate varying

with time

Facility-controlled

Customer-exercised

control

Arrival process

12-19

Distribution of Patient Interarrival Times

0

10

20

30

40

1 3 5 7 9 11 13 15 17 19

Patient interarrival time, minutes

Rel

ativ

e fr

eque

ncy,

%

12-20

Temporal Variation in Arrival Rates

0

0.5

1

1.5

2

2.5

3

3.5

1 3 5 7 9 11 13 15 17 19 21 23

Hour of day

Avera

ge ca

lls pe

r hou

r

60708090

100

110120130140

1 2 3 4 5

Day of week

Perc

enta

ge o

f ave

rage

dail

y ph

ysici

an vi

sits

12-21

Poisson and Exponential Equivalence

Poisson distribution for number of arrivals per hour (top view) One-hour 1 2 0 1 interval Arrival Arrivals Arrivals Arrival

62 min.40 min.

123 min.

Exponential distribution of time between arrivals in minutes (bottom view)

12-22

Queue Configurations

Multiple Queue Single queue

Take a Number Enter

3 4

8

2

6 10

1211

5

79

12-23

Queue Discipline

Queue

discipline

Static(FCFS rule)

Dynamic

selectionbased on status

of queue

Selection basedon individual

customerattributes

Number of customers

waitingRound robin Priority Preemptive

Processing timeof customers

(SPT or cµ rule)12-25

Outpatient Service Process Distributions

0

5

10

15

1 11 21 31 41

Minutes

Relat

ive

frequ

ency

. %

0

5

10

15

1 11 21 31 41

Minutes

Relat

ive fr

eque

ncy,

%

0

5

10

15

1 11 21 31 41

Minutes

Rela

tive

frequ

ency

, %

Second Service

Appointment ServiceWalk-in Service

12-26

Service Facility Arrangements

Service facility Server arrangement

Parking lot Self-serve

Cafeteria Servers in series

Toll booths Servers in parallel

Supermarket Self-serve, first stage; parallel servers, second stage

Hospital Many service centers in parallel and series, not all used by each patient

12-27

Topics for Discussion

Suggest some strategies for controlling variability in service times.

Suggest diversions that could make waiting less painful.

Select a bad and good waiting experience, and contrast the situations with respect to the aesthetics of the surroundings, diversions, people waiting, and attitude of servers.

Suggest ways that management can influence the arrival times of customers.

What are the benefits of a fast-food employee taking your order while waiting in line?

12-33

Interactive Exercise

The class breaks into small groups with at least one international student in each group, if possible. Based on overseas travel, each group reports on observations of waiting behavior from a cultural perspective.

12-34

Thrifty Car Rental

Queue Features Customer Counter Garage Car Wash

CallingPopulation

ArrivalProcess

QueueConfiguration

QueueDiscipline

ServiceProcess

12-35

Eye’ll Be Seeing You How are Maister’s First and Second Laws of

Service illustrated? What good and bad features of a waiting

process are evident? How should Dr. X respond to Mrs. F’s letter? How could Dr. X prevent future incidents? Should customers be rewarded for offering

constructive criticism?

12-36

Sample Letter

Dear Mrs. F.: I offer my deepest apologies for your recent bad

experience on January 5, 1989. The treatment you were shown and the length of time you had to wait is completely inexcusable.

You and the rest of your family are valued patients of mine and I hope this most unfortunate experience does not cause me to lose your patronage. I personally guarantee that this will not happen again.

I hope you will make another appointment with us to have your problem taken care of. This service, of course, will be provided free of charge.

Thank you for expressing your concerns. Please let me know immediately if you have any other problems.

Sincerely yours, Dr. X, M.D.

12-37