Shell Gas Station Analysis

Project Proposal

Project Overview

Customers arrive at a Shell gas station in order to get gas, wash their cars, or both. The gasstation is a standard one consisting of three gas pumps and one diesel pump. The station is opentwenty four hours per day and seven days per week with no downtime for worker shift changes.Once every three days, a truck comes in to fill up the station's underground gas tanks. This is theonly time the station closes for business. The gas station attendant puts up a closed sign and waitsuntil all cars currently pumping gas have left. Then he signals the truck to start filling up the tanks.The truck usually takes 40+/-5 minutes to fill up the tanks.

One person is the gas station attendant who works at the counter. He or she is allowed totake a ten minute break every three hours.

The gas station also has a car wash behind it. In order to wash their cars, customers need toinsert a specified amount of change at the car wash entrance.

Customers come to the gas station depending on the time of day, where we can generallydivide the day into three parts, morning, afternoon, and night. The amount of customers wantinggas always depends on the part of the day.

If all gas pumps are busy, a customer will wait in the one which has the shortest queue. But,if all pumps have a certain number of people waiting to use it, the arriving customer will refuse towait and leave. If they wanted to wash their car as well, they will leave for the car wash, otherwisethey will leave the station and go elsewhere.

If there is less than a certain number of people waiting to use the car wash, the customer whowanted to wash their car will get in the queue. If there is more than a certain number of peoplewaiting in line, the customer will leave. If the leaving customer wanted to get gas as well, they willleave for the gas pump, otherwise they will leave the station and go elsewhere.

If a customer who wants both gas and a car wash did not get either because of the queuelengths, they will leave the station and go elsewhere.

Some customers also choose to wash their windows after pumping gas. While they aredoing so, nobody may use the gas pump they are at.

Components

In the model, a customer will be the GPSS transaction. Therefore the customer is an activecomponent.

The gas station attendant working at the counter will be represented by a GPSS facility. Heis also an active component.

The only resource in the model is the gas, but since there is little chance that the station willrun out of gas, this need not be considered.

All the gas pumps will be represented in the model as GPSS facilities with correspondingGPSS queues for each.

The car wash can also be represented as a GPSS facility with a GPSS queue.

Measurements

Following are the already known data components:

- working hours are 24 hours per day, 7 days per week- 3 gas pumps- 1 diesel pump- every 3 days a truck fills the station's tanks with fuel- the truck takes 40+/-5 minutes to fill up the tanks- 1 person works as the station attendant- the attendant may take a 10 minute break every 3 hours- the day should be divided into morning, afternoon, and night

Following are the components which should be measured by observing the real system:

- need to find out how often customers arrive for each part of the day. This can be simplified by taking measurements at a few different times for each part of the day instead of spending twenty four hours at the station.- need to find out how long it usually takes customers to pump the gas into their vehicles- need to find out how long it usually takes customers to wash their vehicles in the car wash- need to find out the percentage of customers that want only to buy gas- need to find out the percentage of customers that want only to wash their cars at the car wash- need to find out the percentage of customers that want to buy gas first and wash their cars afterwards- need to find out the percentage of customers that want to wash their car first and purchase gas after that- need to find out the average queue length at which the customers will choose to leave, rather than join the queue for the gas pumps- need to find out the average queue length at which the customers will choose to leave, rather than join the queue for the diesel pump. We imagine this will differ from the regular gas pump as there are less diesel pumps in the neighbourhood.- need to find out the average queue length at which the customers will choose to leave, rather than join the queue for the car wash

All this data will have to be input into the GPSS model. One may also choose to take adifferent approach and instead of measuring the percentages of people who want gas, gas and wash,wash and gas, or only wash, one can measure how often a customer that fits in each of these fourcategories appears and have four separate generate statements in the model, one of each customertype.

Also, even though we are confident in our measurements given in the 'known components’part, one can check up on these while making other measurements of the system.

Objectives

The owner of the station wishes to build another one right across the street. He is debatingas to this would be a profitable move.

We want to count all the customers who leave the station with their needs unfulfilled. Wealso want to differentiate between them depending on the need that actually went unfulfilled. So,for example, we want to be able to tell apart a customer who wanted to only wash their car but didnot get a chance to and a customer who wanted both to wash their car and get gas, but only got achance to get gas.

These statistics will allow the station owner to see how many people would come to the newstation and what for, as he assumes that all people who leave the current station with their needsunfulfilled would simply go across the street to the new station.

We also want to pay special attention to the diesel pump. We want to know how manycustomers wanted to purchase diesel but did not get a chance to.

Differentiating between the diesel and the gas pumps will allow the station owner to seewhether he should build the new station with a diesel pump as well or whether he should drop it fora fourth gas pump.

Obstacles

One obstacle in data collection will come from the fact that the gas station is open twentyfour hours per day. Since collecting data for the whole day is impossible unless a large team ofcollectors were working on it, the data will have to be collected from various time slots of the day.These time slots will have to be meaningfully selected in order to accurately represent the wholeday.

Another obstacle is that data collection will require an unobstructed view of both the gaspumps and the car wash in order to see the queue lengths at all times.

There should not be any major obstacles in the model construction, other than keeping trackof what each customer wished to do at the station and what they actually got a chance to do.

Another obstacle is to actually find out what the arriving customers wished for. How can wefind out if a leaving customer is satisfied or disgruntled because they could not use the car wash?