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
Table Of Contents
Page #
Executive Summary
1
Introduction
2
Current Checkout Area Layout – Locations
2
Customer Processing – Events
4
Simulation Approach
7
Modeling Approach
7
Data Collection
8
Data Processing
8
Results
9
Conclusion / Recommendations
13
APPENDIX A – Optimization Spreadsheet
APPENDIX B – Arrival & Service Time Raw Data
APPENDIX C – Processed Data
APPENDIX D – Simulation Input Text Files
APPENDIX E – Simulation Output Test Files
APPENDIX F – Original Project Proposal
APPENDIX G – Final Presentation Slides
Executive Summary:
The objective of this project was to determine whether there exists an optimal combination of selfservice and full service lines that could maximize customer throughput at the Stop & Shop
Supermarket in Hamden, CT. Currently Stop & Shop has installed 5 self-service checkout lines in
addition to the 18 standard full-service checkout lines. Two of the new self-service lines have
been designated for customers with 12 items or less while the remaining 3 lines are designated for
customers with an unlimited number of items.
To compare the performance of the new self-service lines in the existing system, inter-arrival and
service time data was recorded between the hours of 11:00 am and 1:00 pm, peak service times for
Stop & Shop, for each of the four checkout line types: self-service unlimited, self-service 12 items
or less, full-service unlimited, and full-service 12 items or less. This data was then reduced using
Stat::Fit to allow the inter-arrival and service times to be represented analytically. An analytical
simulation model was created with visual process simulation characteristics to analytically reenact the checkout line customer throughput process. Analysis of each of the four service
scenarios, using inter-arrival and servicing times stoichastically represented using a pseudorandom number generating approach with distributions related back to the true arrival rates, was
run to establish the average total number of customers serviced per hour for each check-out line
type. Given a few basic restrictions on the line combinations, all checkout line combination types
were analyzed for two scenarios, lines that accepted an unlimited number of items and those that
accepted customers with 12 items or less, to fully understand the impact of each line combination.
It was also assumed that all service lines would be open for service, a scenario most likely
achievable just before a major holiday like Thanksgiving or Christmas. What was found is that for
the 12 item-or-less checkout lines, installation of the new self-service 12-item-or-less isles
provided no increased customer throughput. This was due mostly to the fact that of the 5 possible
12-item-or-less checkout lines, the full-service lines were much more efficient in servicing
customers than the self-service lines. For the checkout lines that allowed an unlimited number of
items, it was also found that the addition of the new self-service lines actually limited customer
throughput. In fact, converting all chekcout lines back to the original full-service configuration
provided the highest customer throughput.
So, based on the original request, there is no customer throughput benefit to be had by installing
any additional self-service checkout lines. However, considering the cost benefit that could be had
by eliminating the checkout personnel required in a full-service checkout line, a financial benefit
outside the scope of this study may reveal a significant operating cost reduction.
Page 1
Introduction:
Stop & Shop currently provides two grocery checkout methods: full-service checkout and selfservice checkout. The full-service checkout lines use the traditional checkout method. Customers
load their groceries or items onto a convey, a Stop & Shop associate scans the items while another
associate, if available, bags the scanned items and places the filled bags in the customers shopping
carriage. The self-service checkout method allows customers to scan their items, pay for their
purchase and bag without the interaction of any Stop & Shop associate. Of the 23 total checkout
service lines, Stop & Shop recently replaced 5 full-service checkout lines, with self-service
checkout lines while the remaining 18 service lines retain full-service status. The entire checkout
area currently occupies 146.5 feet of floor space at the front of the store. Within this space, three
fundamental checkout line widths exist. Self-service lines are 5.5 feet wide. Most full-service
lines are 6.5 feet wide while 4 full-service handicap accessible lines are a full 7 feet wide.
Although the new self-service lines appear to process customers a bit slower than any of the full
service lines, their narrower width, the result of eliminating a checkout associate, may prove to be
beneficial by allowing the installation of more self-service checkout lines in the same floor space.
Aside from the obvious reasons for installing the self-service checkout lines (i.e. the elimination of
some checkout associates), Stop & Shop wants to know whether the overall customer throughput
could also be improved by replacing more full-service checkout lines with the narrower selfservice lines. The focus of this study was to determine the optimum checkout line configuration
that maximizes customer throughput at the maximum customer service load.
Current Checkout Area Layout - Locations:
As mentioned earlier, 23 checkout lines accommodate the customer checkout as shown in Figure
1. As the figure shows, the five self-service checkout lines reside on the far left had side of the
Enter
Exit
Carriage
Area
Customer Service Area
Self-Service
12 or Less Unlimited
23 22 21 20 19 18
Carriage
Area
Full-Service, Unlimited
17
16
15
14
13
12
11
10
9
8
7
6
5
4
Enter
Exit
Full-Service
12 Items or Less
3
2
1
Figure 1
Page 2
checkout area. Also identified are those lines that target customers with 12 items or less as well as
those lines designated for handicap access.
Full Service Checkout Lines
As mentioned earlier, each standard full service line, whether it is designated to serve customers
with an unlimited number of items or customers with 12 items or less, measures 6 ½ ft wide as
depicted in Figure 2. For convenience, 4 of the 18 total full service checkout lines measure
Full Service Checkout Line Configurations
Bagging
Associate
Unlimited
Standard Width
6 ½ ft
Unlimited
Handicap Width
7 ft
12 or less
Handicap Width
7 ft
12 or less
Standard Width
6 ½ ft
Arrival Queue
Feeder
Conveyor
Checkout
Associate
Service
Location
Gathering
Area
Exit
Figure 2
a full 7 ft wide to enable handicap access. The current full service checkout area utilizes 119 ft of
floor space. Of the 18 full service lines, 2 lines are designated for customers with 12 items of less
with 1 of the 2 lines 12 item or less lines for handicap access. The remaining 16 full service
checkout lines currently allow service for customers with an unlimited number of items and are
comprised of 13 standard width checkout lines and 3 wider handicap access lines. Each unlimited
checkout line requires two checkout associates, the scanning associate and a bagger. The two
Page 3
checkout lines that accommodate 12 items or less only require one associate to perform both
duties, scanning and bagging.
In general, three processes take place in the full-service checkout system. There are customer
arrivals, services, and exits. Arrivals occur in all lines on the left hand side of the checkout line.
The customer loads their items onto a conveyor where they are fed to a checkout associate. The
checkout associate scans the items and, depending on the line type, will either bag the items or
send them off to a bagging associate. Near the end of the checkout process, the customer proceeds
to a payment location, pays the checkout associate and then exits the checkout system.
Self-Service Checkout Lines
Each of the 5 self-service checkout lines shown in Figure 3 measure 5 ½ ft wide, regardless of
their designation (12 items or less or unlimited). Upon arriving at the checkout line, customers
Self Service Checkout Line Configuration
Unlimited or
12 or less
5 ½ ft
Arrival Queue
Service
Location
Transfer
Conveyors
Gathering
Area
Exit
Figure 3
congregate in the usual fashion, which is at the entrance to the checkout line. Unlike the fullservice system, items are scanned at the beginning of the checkout line and are then placed on a
series of conveyors. The conveyors carry the items to a gathering area where it is then the
customer’s duty to bag their own groceries. The gathering area can easily accommodate up to 20
items. However, depending on the number of groceries a customer has, a situation may arise
where the customer will have to stop scanning items because no other items can fit in the gathering
area and the system has begun to back up. When this occurs, the customer must remove (bag), the
groceries in the gathering area before additional items can be scanned. Once all items have been
scanned, the customer pays through an automated payment system. At this time, coupons can also
be scanned. The self-service system will accept all forms of payment, the easiest of course being
performed using a credit card. Once the payment process is complete the customer exits the
system.
Customer Processing – Events:
Regardless of the service line configuration, each customer follows the same event sequence.
Customers arrive, service is performed, and customers exit. In real life though, many other mini
Page 4
processes take place that are very difficult to quantify. The following event sections contrast the
differences between actions that happen in real life to those that can actually be quantified for
simulation.
Arrivals
Each of us have been to the super market and encountered this same scenario. When it comes to
checkout and based on our past experience, a whole litany of subjective logic processing goes
through our mind when selecting the checkout line that will get us serviced the fastest. At first,
typically we will observe each of the open checkout lines to determine which appears to have the
shortest arrival queue. Usually the observation only extends to within 5 or 6 checkout lines away
from the initial approach into the checkout area. From these few lines, we’ll then observe how full
the carriages or basket are for the customer(s) in front of us. Then based on the number of items in
the proceeding customers carriage, checkout line selection is made. This may mean that we might
select a checkout line with an arrival queue that has more people in it than another arrival queue,
but the proceeding customers have far fewer items than the arrival queue with fewer customers.
However, sometimes, the advantage of one line over the other is indistinguishable. If shopping
alone, one might find them self shifting back and forth between lines based on each lines
instantaneous progress. Or if shopping with a companion, one might reserve a turn in one line
while the other remains with the carriage or basket in another line, all the while continuously
assessing the progress of each respective line to once again, determine what will get them serviced
the fastest. This technique however complicates the selection process for newly arriving
customers. Newly arriving customers often will have this technique unveiled to them at the most
inopportune time. The newly arriving customer may have made a line selection with the premise
that a line appeared faster based solely on fact that each proceeding customer appeared to have
fewer items for checkout than any of the other lines. After a short amount of time in the arrival
queue, the ploy unfolds to the chagrin of the newly arrived customer so that now the carriage
bearing companion moves into the line of their compatriot who originally appeared to have little or
no items for checkout. Does the newly arrived customer leave the arrival queue based on the new
circumstances or not? Sometimes they do and sometimes not.
For the full-service checkout lines, the arrival process continues into the checkout line itself with
items being loaded onto the feeder conveyor. Termination of the arrival process is signified with
the scanning of the new customers first item.
For the self-service checkout lines, observation revealed that patrons would enter or not enter a
line based on the number of customers in the line, number of items in a proceeding customers
shopping cart or basket, or the confidence level exuded by the proceeding customer (for instance,
if a customer appears to be confused, their line may be skipped for another line whose customer is
fluidly processing their items). Those lines that serviced customers that appeared slow to process
items were passed over for other lines with often more patrons but that seemed to move at a pretty
smooth pace.
Servicing – Full Service
By the time the customer is about to begin service, some if not most of their items have been
Page 5
loaded onto the feeder conveyor. Servicing is initiated with either the scan of a “scan saver” card,
which acts like a virtual savings coupon, or the scan of the first item. During the scanning process,
the customer may either continue to load more items onto the feeder conveyor as more room
becomes available or may assist with the bagging of scanned items. Once all of the items have
been scanned, coupons, if any, are then scanned for additional savings.. Payment arrangements are
negotiated and the payment transaction is completed. If not all the items have been bagged, the
checkout scanning associate will also assist in bagging the remaining items. Once all of the items
have been bagged from the collection area, the next customer begins processing, even before the
proceeding customer has left the checkout line.
On occasion, significant delays can be had if an item is not properly marked and does not have a
price tag on it. If this situation occurs, another associate is called upon to retrieve another item
that is properly marked or that has a legitimate a price on it. These types of situations can delay
the servicing process several minutes, which is a high percentage of the total time that the
customer spends getting serviced.
Servicing – Self Service
The self-service system does for the customer exactly what its name implies. It allows the
customer to scan their own items, use coupons, and pay on their own without the interaction of any
store associate. From time to time, a problem will arise during the checkout process. To handle
these instances, Stop & Shop has up to three customer service representatives that circulate
between each of the five self-service checkout lines to assist customers in their checkout process.
Unlike the full service checkout system, self-service processing begins at the beginning of the selfservice checkout line. Customers arrive at the self-checkout line and begin scanning immediately.
There is no intermittent loading of a feeder conveyor. Items are taken directly from the carriage or
basket, scanned at the scanner, and placed on a conveyor where they are taken to the collecting
area of the checkout line. Now here’s where the checkout process can get a little complicated if
the whole process is not executed flawlessly. If a customer misses the scan of an item but places
that item on the conveyor anyway, the system will be alerted to the fact that an item has passed
through the system without being scanned. In this instance, typically the conveyor will reverse
direction to bring the item back to the customer. More often than not, though this will cause a
failure in the system requiring one of the customer service associates to assist the customer with
the problem. Customers with coupons also face a high chance in processing delay as the coupon
entry process can be very sensitive. Also complicating the checkout out process is the handling of
produce since there are no barcodes on most produce items. For this, the self-service system
provides a lookup system through which the customer searches for the correct produce item match.
Lack of familiarity with the system often delays the checkout process.
Once the customer has finished scanning their items, the coupon process is completed and the
customer selects the finish and pay option. The self-service system currently accepts credit and
debit cards directly as well as good old cold cash. Checks can also be accepted, but customers will
have to proceed to one of the customer service associates for further assistance.
Page 6
Exits
Regardless of the checkout system, all system exits are the same. Each exit usually entails the
customer gathering them self together while still in the checkout line. With receipts and wallets
stowed, the customer proceeds to exit the checkout line and merge into all other exiting traffic.
Occasionally exits can be delayed if an item has been forgotten to be scanned because it was under
the carriage and wasn’t noticed during the scanning process. For this, the item is then rung up and
the customer will have to complete the paying process all over again.
Simulation Approach:
Given all of the above arrival, processing and exit descriptions, it became evident very quickly that
accurately simulating the system checkout process could become a daunting task. Furthermore,
my request at the local Stop & Shop to collect data was well received but limited the scope to
which data could be collected. I was allowed to take as much data as I wanted so long as my
observations were unobtrusive and I did not interact with the customers or get in the way of the
whole process. Given these restrictions, at best the only data that could be compiled had to be
limited to what I could see without getting too close to the checkout system. For this, all that
could be observed were arrivals and the servicing process, which enormously narrowed the scope
of this simulation effort. Therefore, a number of assumptions and guidelines were established to
more appropriately fit the scope of this project given the amount of data that was available. These
assumptions are outlined in the following section.
Locations:
12 Items-or-less
1 line will remain full-service and handicap accessible.
4 lines may be full or self-service.
Unlimited number of items:
3 lines will remain full-service and handicap accessible.
15 lines may be full or self-service
Checkout Floor Area Width
Although the current configuration exists within a discrete floor area envelope, it is
foreseeable that when optimizing the various checkout configurations, slightly more or less floor
space will be required to accommodate the optimized throughput configuration. Therefore, it will
be acceptable that the floor area breadth required be no more than an additional 50% of the widest
checkout line, or 3 ½ ft.
Modeling Approach:
Fortunately, the processing that occurs at the checkout line is a simple process, essentially a single
server system that can be represented by a GG1 or am MG1 (one instance) queueing process.
However, with 4 locations designated in the checkout process; the arrival location, the arrival
queue, the checkout location and an exit location, 23 total checkout lines with 4 locations per line
exceeds the modeling capacity of ProModel’s Student Version. Because of this, two modeling
Page 7
requirements became disallowed. First, the entire checkout system could not be modeled all at
once, and second, because the entire system couldn’t be modeled, Sim Runner also couldn’t be run
to optimize the checkout system. Granted, the number of locations could have been reduced from
4 to 2 (an arrival queue and a service location), but with 18 + unlimited service combinations
alone, this would require a minimum of 36 locations which still far exceeds the Student Edition’s
capacity.
To simplify the process, it was then assumed that each checkout line type would perform
consistently for that checkout line type. What this means is that by simulating the performance of
just one line, with little standard deviation, the total number of exits per hour could be calculated.
This data could then be input into an excel spreadsheet where all combinations could be analyzed
in a table. Given this approach, each processing type was run until so that the 95% confidence
interval was satisfied. Once this condition was met, the average customer throughput per hour was
calculated and input into an optimization spreadsheet as shown in Appendix A. Two separate
sections were set up in the spreadsheet. The first section was used to analyze the Unlimited Item
checkout line combinations, while the second section was used to analyze the 12-item-or-less
checkout line combinations.
Data Collection:
A total of four hours (2 people collecting data for 2 hours) of data was collected on the processing
of customers through each of the four types of checkout lines. A Sunday was chosen, between the
hours of 11:00 am and 1:00 pm to collect data as this time has been found to be, in general, one of
the busiest times of the day for the supermarket. When recording arrival data, a customer arrival
was recorded when a customer actually entered a line for service. Customers that slowed to where
a line began but then moved to the next (better) line were recorded to have arrived once they
entered the line that they stayed in, not when they entered the arrival line area. When collecting
service time data, service was recorded as having begun when the customer’s first item was
scanned, which could be either a grocery or scan-saver card. Service ended either when the next
customer in line scanned their first item, or in the event there wasn’t another customer in line,
when the customer exited the checkout line all together. The arrival and service time data can be
found in Appendix B.
Data Processing:
With the data collected, each arrival and service data point was entered into Stat::Fit to determine
the best analytical representation of the data. Once in Stat::Fit, all of the standard data processing
tests were performed on the data, which included running the autofit function, on each of the eight
data sets (4 arrival data sets and 4 service data sets). The top four best analytical data fit
approximations were then tested in each of the four simulation models for accuracy and to
determine whether the results made sense. Some of the analytical approximations that scored the
highest in the autofit test performed terribly when applied to the simulation models. For the
arrivals, one criteria that was used to determine whether the analytical arrival rate approximation
was valid was to run the simulation and then look at how many customers accumulated in the
arrival queues. In practice, not more than 4 or 5 customers would be waiting in any of the arrival
Page 8
queues at any one time. If the simulation predicted more customers waiting in the arrival than
ever observed, the analytical arrival rate was rejected and another arrival rate tested. It should be
noted though that the length of the arrival queue is also closely coupled to the service times. This
often resulted in the running of numerous arrival and service time combinations before a sensible
combination could be arrived upon. Fortunately though, service times were usually well behaved
and gave few good options aside from the better fit analytical approximations. Therefore, more
often than not, analytical service times were represented by the highest ranked curve fits.
Results:
After completing each of the simulation scenarios, it was found, as shown in Figures 4, 5 and 6
that Stop & Shop achieved the highest customer throughput with no self-service checkout lines.
F u ll S e r v ic e
H a n d ic a p p e d ( F S )
S e lf S e r v ic e
500
18
450
16
400
14
350
12
300
10
250
8
200
6
150
4
100
2
50
0
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Total Customer Throughput
T o ta l Ex its
20
Curve
Enlarged
Below
16
C h e c k o u t L i n e C o m b i n a ti o n s
Fewer Self Service
Checkout Lines
Total Customer Throughput
Number of Checkout Lines
Total Customer Throughput for
Figure 4 Given Checkout Line Configurations
Unlimited Item Lines
460
Total Customer Throughput for
Given
Checkout Line Configurations
Figure 5
Unlimited Item Lines
450
440
430
420
410
400
390
380
370
360
350
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
C h e c k o u t L i n e C o m b i n a ti o n s
Fewer Self Service
Checkout Lines
Page 9
F u ll S e r v ic e
H a n d ic a p p e d ( F S )
S e lf S e r v ic e
T o ta l C u s to m e r Ex its
9
400
8
350
7
300
6
250
5
200
4
150
3
2
100
1
50
0
0
1
2
3
4
Total Customer Throughput
Number of Checkout Lines
Figure 6
Total Customer Throughput for
Given Checkout Line Configurations
12 or Less Lines
5
C h e c k o u t L i n e C o m b i n a ti o n S c e n a r i o s
Therefore the original hypothesis that additional customer throughput could be had with some
combination of full and self-service lines by the virtue that the self service lines were narrower,
was false. However, given the savings that could be had by eliminating some of the staff required
to man the full service lines, it was found that there were other line configurations that did reduce
the manpower required but still maintained similar customer throughput. They are presented in
the following sections.
Unlimited Item Service
As Figure 7 shows, a maximum customer throughput of 446 customers per hour is achieved with
U n lim ite d Q u a n tity C h e c k o u t L in e s
T o tal Cu s to m e r s Se r ve d p e r h o u r
450
H ig h e s t Th ro u g h p u t
446
L in e C o n fig u ra t io n
445
M o re Th a n 5 0 % F u ll
440
S e rvic e
C u rre n t S e rvic e L in e
435
C o n fig u ra t io n
430
425
426
425
420
415
410
Figure 7
Page 10
all unlimited checkout lines configured as full service lines. In retrospect, this makes perfect sense
since the efficiency and fluidity of the checkout operation is no better achieved than in the hands
of a trained checkout associate. However, if Stop & Shop’s ultimate goal is to minimize operating
costs at the expense of reduced customer throughput, than some other options exist. The current
installation, which utilizes 3 self-service unlimited item checkout lines with the remaining 15
checkout lines configured for full-service operation, can achieve a simulated throughput of 426
customers per hour. Analysis showed though that another checkout service line configuration that
utilizes 7 self-service checkout lines and 12 full-service checkout lines could yield a simulated
throughput of 425 customers per hour, just one customer less than the current configuration. The 7
self-service checkout line configuration is able to compete with the current 3 self-service line
configuration by allowing the installation of an additional checkout line without taking up more
floor space. Each line configuration discussed in this section is presented in Figure 8.
Num be r of Se rvice Line s
U n lim ite d Q u a n tity C h e c k o u t L in e C o n fig u ra tio n s
16
F u ll S e rvic e
14
H a n d ic a p p e d (F S )
12
S e lf S e rvic e
10
8
6
4
2
0
H ig h e s t Th ro u g h p u t
M o re Th a n 5 0 % o f
C u rre n t
C o n fig u ra t io n
L in e s F u ll S e rvic e
C o n fig u ra t io n
Figure 8
C h e c k o u t L i n e C o n fi g u ra ti o n s
12 Items-or-Less Service
As shown in Figure 9, the maximum customer throughput of 338 customers per hour for customers
with 12 items or less is achieved, as was true with the unlimited item service lines, with each
checkout line configured for full-service processing. Like before however, if operating cost
becomes a heavily weighted attribute to trade, especially considering that the number of items per
customer is so low for this type of checkout line, the current configuration may provide a savings
not quantifiable through this study even though its throughput is significantly less at 238
customers per hour. Ultimately, because there are so few 12 item of less checkout lines, there is
little latitude when trying to take advantage of the size benefit offered by the narrower self-service
checkout lines, for any real throughput performance to be realized. Each line configuration
discussed in this section is presented in Figure 10.
Page 11
Tota l Custom e rs Se rve d pe r hour
1 2 Ite m s o r L e s s C h e c k o u t L in e s
400
H ig h e s t Th ro u g h p u t L in e
338
350
C o n fig u ra t io n
C u rre n t C h e c k o u t L in e
298
300
C o n fig u ra t io n
3 S e lf-S e rvic e C h e c k o u t
258
250
L in e s
200
150
100
50
0
Num be r of Se rvice Line s
Figure 9 1 2 Ite m s o r L e s s C h e c k o u t L in e C o n fig u ra tio n s
5
F u ll S e rvic e
H a n d ic a p p e d (F S )
4
S e lf S e rvic e
3
2
1
0
H ig h e s t Th ro u g h p u t
C u rre n t
3 S e lf S e rvic e
C o n fig u ra t io n
C o n fig u ra t io n
C h e c k o u t L in e s
Figure 10
C h e c k o u t L i n e C o n fi g u ra ti o n s
Page 12
Conclusions / Recommendations:
If everyone worked for free, i.e. employee cost was not an issue, the hands down conclusion from
this study is that Stop & Shop should replace all of the new self-service with the old full-service
checkout lines, regardless of the checkout line type. However, nobody works for free so the
decision becomes a bit more complicated and unfortunately, is best answered with the aid of
collaborating data outside the scope of this study. Other data that would also help to understand
the process would be the number of items each customer purchases and at what cost. It was
observed that customers that had very full carriages typically migrated to the full-service checkout
lines. This data would further help justify the existence of the checkout associate since not only do
the full-service lines service more customers per hour, on average, they’re also moving more items
through the system which compounds the profits.
After speaking with the Stop & Shop manager, the real reason for Stop & Shop’s recent
installation of the self-service checkout systems is that, on the off peak hours when few customers
are in the store, usually at around 11:00 at night, the new 5 self-service lines are always available
and open to service these customers. And for these times, when it is difficult for Stop & Shop to
predict the number of checkout associates needed to staff the checkout system, S & S can always
plan on having at just one full service line open with the overflow being handled by the selfservice systems.
In closing, a conclusion can be had from this entire study and from that comes a recommendation.
It is clear that there is no immediate replacement for the efficiency and capacity of the full-service
checkout system, at least not for the next 15 years. There will always be a need, for one reason or
another for the full-service checkout system. But, since Stop & Shop has gone beyond the point of
mere alternate system consideration and have actually installed an alternative checkout method, it
would follow that if they will entertain one system, they will entertain others. My suggestion to
meet the requirements of both worlds is to replace all of the current checkout lines with a hybrid
system, a system that would enable both self-service and full-service. With this, Stop & Shop
would have the best of both worlds… maximum customer throughput on those super busy
occasions and nearly unrestricted throughput the rest of the time. In fact, with so many checkout
lines open for service, arrival queues would more than likely shorten allowing for more compact
arrival queue areas in the store. The details of such a system have yet to be worked out fully, but
are best left as a venture for the suggesting party.
It would be unfair if I did not give a special thanks to Mr. Guy Pititto and Mr. Mike Smith, both
managers of the Hamden, CT Stop & Shop, for their valuable insight and for allowing me to
collect data at their store. I would also like to thank my wife Sarah for here enormous help in
collecting that data.
Page 13
APPENDIX A
Optimization Spreadsheet
APPENDIX B
Arrival & Service Time Raw Data
APPENDIX C
Processed Data
APPENDIX D
Simulation Input Text Files
APPENDIX E
Simulation Output Text Files
APPENDIX F
Original Project Proposal
Discrete Event Simulation Project Proposal
Class:
Name:
Date:
To:
DSES - 6620 Simulation Modeling And Analysis
Kevin Lewelling
February 17, 2002
Professor Ernesto Butierrez-Miravete
Background:
Over the past year, the Super Stop & Shop store on the corner of Skiff St. and Dixwell Ave. in
Hamden, CT has installed two new self-service systems. The first system was installed in the deli
department and allows shoppers to place orders using an interactive touch screen computer system.
The second self-service system allows shoppers to self-serve themselves through the checkout
process.
Two systems have been implemented for the self-service checkout system. The earliest system
targetted shoppers with 20 items or less. This system was configured with four checkout stations
with a single customer service associate located in a central location as shown in Figure 1.
Following what appeared to be a successful trial period, Stop & Shop imstalled a new self-service
checkout system, shown in Figure 2, which was re-oriented to the traditional isle type configuration.
The new system not only has two isles designated for shoppers with 12 items or less but also has
three new isles that can accommodate as many groceries as you care to scan. For the new system,
S&S has hired two customer service associates that circulate between the checkout isles to aid
shoppers in their checkout process. None of the checkout systems have employees dedicated to
bagging groceries
Figure 1 - Stage I Self-Service Checkout System
Station 1
Scan
Pay &
Bag
Station 2
Scan
Pay &
Bag
Customer
Service
Desk
Waiting Area for
Shoppers Ready
for Checkout
Scan
Arrivals
Pay &
Bag
Station 3
To Processing at Customer Service Desk
Exit
Scan
Pay &
Bag
Station 4
Pay
Bag
Scan
Pay
Bag
Scan
Pay
Bag
Scan
Pay
Bag
12 Items
or Less
Scan
No
Limit
Waiting Area for Shoppers Ready for checkout
Figure 2 - Stage II Self-Service Checkout System
Problem Statement:
Stop & Shop grocery stores have implemented the use of self-service checkout lines to reduce
operating costs. This is accomplished by eliminating both a cashier and a food packaging associate
normally required in each checkout line. Furthermore, by removing the cashier, who is typically
located in part of the isle, the new self-service checkout systems can be narrower and therefore
require less floor space. Although the self-service lines process shoppers a bit slower than the
conventional checkout line, due to shoppers being unfamiliar with the system and inevitable hangups, total shopper throughput may be increased by being able to add more checkout lines in the same
amount of space. Stop & Shop wants to know if they should install more self-service checkout lines
to maximize shopper through put based on the floor space available. The focus of this study will be
to determine the optimum number of self-service lines required to maximize shopper through put
based on the floor space available in the checkout area.
Approach:
An initial visit will be made to the Stop & Shop super market to accurately document the
configuration of each checkout line. A Pro-Model simulation model will then be created based on
the configuration schematic. A separate visit will be made to collect arrival and processing data for
each checkout line configuration. This will include data from both of the full service checkout lines,
12 items or less and the unlimited lines, as well as data from both self-service checkout lines, again
12 items or less and the unlimited lines. Roughly 1 hour of data will be collected for each checkout
line for a total of 4 hours of data. Data will be collected on a weekend to ensure minimal idle time in
each of the checkout lines. A simulation will be run to baseline the current configuration and to
determine the current maximum customer through put. An optimization routine will then be run,
varying the number of individual checkout line configurations, to determine the optimum
combination of full and self-service checkout lines.