Managing Waiting Lines

Learning Objectives

• Describe how queues form.

• Apply Maister's two “laws of service.”

• Discuss the psychology of waiting.

• Describe the essential features of a queuingsystem.

• Explain the equivalence of Poisson arrivalrates and exponential time between arrivals

Lines and Waiting

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

Pete Townshend, Magic Bus

Where the Time Goes

In a life time, the average

American will spend--

SIX MONTHS

Waiting at stoplights

EIGHT MONTHS

Opening junk mail

ONE YEAR

Looking for misplaced 0bjects

Unsuccessfully returning

TWO YEARS phone calls

FOUR YEARS Doing housework

FIVE YEARS Waiting in line

SIX YEARS Eating

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”

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).

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.

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

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

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)

The Art of Service Recovery“To err is human; to recover, divine”

• Measure Cost of Lost Customer

• Listen Carefully

• Anticipate Need for Recovery

• Act Fast

• Train Employees

• Empower the Frontline

• Inform Customers of Improvement

Essential Features of Queuing Systems

DepartureQueue

discipline

Arrival process

Queueconfiguration

Serviceprocess

Renege

Balk

Callingpopulation

No futureneed for service

Arrival Process

Static Dynamic

AppointmentsPriceAccept/Reject BalkingReneging

Randomarrivals withconstant rate

Random arrivalrate varying

with time

Facility-controlled

Customer-exercised

control

Arrival process

Distribution of Patient Interarrival Times

0

10

20

30

40

1 3 5 7 9 11 13 15 17 19

Patient interarrival time, minutes

Rela

tive

freq

uenc

y, %

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

60

70

80

90

100

110

120

130

140

1 2 3 4 5

Day of week

Perc

enta

ge o

f ave

rage

dai

ly

phys

icia

n vi

sits

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)

Queue Configurations

Multiple Queue Single queue

Take a Number Enter

3 4

8

2

6 10

1211

5

79

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 rule)

Outpatient Service Process Distributions

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

, %

0

5

10

15

1 11 21 31 41

Minutes

Rel

ativ

e fre

quen

cy, %

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

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?

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.

Eye’ll Be Seeing You

• How are Maister’s First and Second Laws ofService illustrated?

• What good and bad features of a waiting processare evident?

• How should Dr. X respond to Mrs. F’s letter?

• How could Dr. X prevent future incidents?

• Should customers be rewarded for offeringconstructive criticism?

Pronto Pizza

• Draw a process flow diagram and identify the bottleneck operation.

• Calculate the expected waiting time in the order preparation queue. Compare this value with your simulation result.

• Use the ServiceModel computer simulation software and the Pronto.pkg file to determine the number of drivers that minimizes the total cost of salaries and guarantee discounts.

Pronto Pizza (cont.)

• Based on your simulation recommended staffing level, what is the probability of paying off on the guarantee?

• What do you think of this service guarantee policy?

• What other design or operating suggestions could improve Pronto Pizza’s performance and customer service?