Decision making requires data which often can be obtained from observation. For example, determining when a restaurant is busy is possible by collecting data on the times that people arrive and
depart. Based on this information, the owner of the restaurant can determine how many workers
should be scheduled at different times during the day.
However, there are situations where information gathering like this may be very difficult or impractical. To assist in these kinds of decisions, computer modeling can be used. Using an object
oriented language (like Java) together with basic data structures that we have covered so far in
class, we will be applying a technique known as discrete event simulation to gather data and create
a report. Discrete event simulation is based on the creation of objects that represent each of the
components in the system. Time is modeled using an agenda (or priority queue) where future
events are scheduled in chronological order. Only time steps where an event occurs are considered
by the simulation program, which is quite efficient.
Suppose the popularity of a bus route has increased and now the customers are complaining about
longer waits and full buses. In order to keep ridership up, the bus company has decided to run
a simulation to help figure out whether they should add more buses along this route or buy
larger buses for the route.
The company wants to minimize the average travel time (wait time + ride time). However, they
also want to maximize the Passenger Miles Per Gallon (PMPG). The PMPG is calculated by
multiplying the Miles Per Gallon of the bus by the Average Occupancy of the vehicle. Normal
Buses run at 6MPG and hold 40 passengers, while Extended Buses run at 4MPG and hold 60
passengers. In the case that both these buses are run at full capacity all the time they have the
same PMPG; however, in practice they may not be run at full capacity (to reduce wait time). You
are tasked to create the simulation and return a report with your findings.
The Car Wash example that we “acted out” in lecture has many parallels to this project. You may
find it helpful to use some of the code for the Car Wash example in your simulation project, and
that is O.K. Specifically, you should use the priority queue (PQ.java) as-is. Be sure to credit any
code “borrowed” from the posted lecture examples.
We will assume the following adjustable system parameters:
• A variable number of buses.
• Bus lengths, i.e. you may have a mix of larger and normal sized buses.
CSCI 1933 PROJECT 4 SETUP
• A variable average inter-arrival rate of passengers at each stop (this will be referred to as the
We will assume the following constraints:
• Passengers will be passive, but they will contain data such as:
– Time they arrived at the stop
– Destination/stop they want to go to
– Direction of the stop they want to go to (eastbound or westbound)
• Arrival of a passenger at a stop will be provided by an arrival class that will generate arrivals
for all the stops (determined statistically, see below)
• Wait/travel time will be determined by arrival time and passenger count (see below)
• If a passenger cannot get onto the bus (when the bus is full) they must wait for the next one
Simulation of the system is achieved by creating classes to model the behavior of each element
of the system as well as each activity (event) that occurs in the system. There is NOT an
overall controller that calls for actions to happen at particular times except for a main driver loop
that runs queued events until time runs out. Each element in the system models its own behavior
and interactions with other elements in the system. Each NON-passive element class has an Event
class associated with it. The associated event defines a run() method (as discussed in lecture) that
simulates the specific behavior of that event.
Some of the classes that we will want are:
• Bus Stops (Stop) – contains Passenger queues
• Agenda (PQ)
• Event – an interface for all our events
• BusEvent – occurs each time a Bus arrives at a stop
• PassengerEvent – one occurs for each Passenger arriving at a stop
Let’s look at each of these components, and see what they should contain. Please note that you
may need to include other information, but what is given here is considered fundamental.
This is instantiable once for each Passenger creation event. One PassengerEvent will be made for
each stop, allowing you to have some stops that are more popular than others. This will implement
the Event interface similar to how the CarMaker class was implemented as described in lecture.
PassengerEvent will reschedule itself (using the agenda), create a Passenger, decide where they
want to go on the route, which direction that is from the current stop, and place the Passenger in
the appropriate queue at the current stop.
CSCI 1933 PROJECT 4 SETUP
This is instantiable once for each stop on the route. Each Stop will have two queues associated
with it (one for eastbound passengers and one for westbound passengers), and a name to designate
which stop it is on the route.
Info: University Ave and 27th Street SE and Union Depot each only need to have one
queue, since passengers who arrive at those stops cannot go further east or west, respectively.
There are exactly 10 bus stops:
• University Ave and 27th Street SE
• Raymond Ave Station
• University Ave and Fairview Ave
• University Ave and Snelling Ave
• University Ave and Lexington Parkway
• University Ave and Dale Street
• University Ave and Marion Street
• Cedar Street and 5th Street
• Minnesota Street and 4th Street
• Union Depot
This implements the Event interface. A BusEvent is created for every arrival of a bus at a stop.
When a bus arrives at a stop, the BusEvent causes the bus associated with it to look at its passenger
list to see if there are passengers that wish to exit the bus. If there are, the bus removes those
passengers. The BusEvent will then look at passengers at the Stop that want to go the direction
the bus is going and put as many of them as possible on itself. Finally, the BusEvent will create
a new BusEvent and schedule it (via the agenda) for the arrival at the next stop at a time in the
future depending on the number of passengers that got off and got on. If the Bus has reached the
last stop on either side, it will start going the other direction. For example, if an eastbound bus
arrives at the Union Depot Stop, it will then leave the Union Depot Stop going westbound.
This is the priority queue (likely to be called the agenda within your code). This code is provided.
You will need one instance of it. This one instance will be used to schedule all events for your
CSCI 1933 PROJECT 4 SETUP
You will want to keep track of relevant Statistics such as:
• How full each bus is
• The maximum time a passenger spends waiting at a stop
• The maximum queue length at a stop
You will need to use a random distribution to model the arrival of Passengers at each stop. This
is determined by method calls made in the run() method for the PassengerEvent. You will also
need to randomly generate which stop each Passenger wants to go to.
For the arrival of passengers at a stop, you should start with an average inter-arrival rate of 1
Passenger every 120 seconds. But, you will want to run your model with both higher and lower
demand by decreasing and increasing this inter-arrival time. To more realistically represent the
pattern of arrival of Passengers, we will introduce some randomness according to the table below
(calculations shown using a 120 second inter-arrival time as an example):
• 10% of the time: 75% above average arrival interval (120 + 0.75 × 120)
• 15% of the time: 50% above average arrival interval (120 + 0.50 × 120)
• 20% of the time: 20% above average arrival interval (120 + 0.20 × 120)
• 10% of the time: right at average arrival interval (120)
• 20% of the time: 20% below average arrival interval (120 − 0.20 × 120)
• 15% of the time: 50% below average arrival interval (120 − 0.50 × 120)
• 10% of the time: 75% below average arrival interval (120 − 0.75 × 120)
Downtown stops (listed below) are more popular than others, therefore, at these stops passengers
should arrive 50 percent more frequently than at normal stops. They are also *two* times as likely
to be a destination for a passenger than another stop.
Of the 10 stops, there are 3 downtown stops (Cedar Street and 5th Street, Minnesota Street and
4th Street, and Union Depot), and 7 normal stops (those not listed in the downtown category). If
we sum the weight (likelihood) of each stop, we get 13 (2 × 3 + 1 × 7). This means each downtown
stop has a 2/13 chance of being chosen, and each other stop has a 1/13 chance of being chosen.
Determining processing time
To determine the amount of time a bus will take between stops, we use these rules:
CSCI 1933 PROJECT 4 WHAT TO DO
• A bus will take 3 minutes (180 seconds) between each stop
• A bus will wait for at least 15 seconds at each stop
• It takes a passenger 2 seconds to get off and 3 second to get on
Therefore, a bus will take at least 3 minutes and 15 seconds to get from one stop to another. If
the time it takes passengers to get on and get off is larger than 15 seconds, it will take 3 minutes
plus the amount of time it took for passengers to get on and off. Even though each stop isn’t the
same distance from the next one, the times between each stop has been simplified to make the
• Assume that passenger arrival distribution and destination stop will use the distributions
• Assume that the maximum number of buses is 18 (one for each stop going each direction)
– Buses at University Ave and 27th Street SE and Union Depot cannot go any further east and west respectively. Consequently, there can only be at most 18 buses running
at a given time.
• Use the rules above for calculating the amount of time between each stop for a train.
• Load: the average inter-arrival rate of passengers
• Number of buses (1-18, this can also be considered the frequency of buses)
• Bus Size
What to do
First, get the simulation system to work, but start small and verify each feature works before
proceeding to the next one. Then, produce a detailed report that gives a convincing presentation
for what the bus company needs to do to satisfy its customers while maximizing their fuel economy.
In order to provide a convincing argument, you will need to collect good statistics, verify them,
and present them in a clear manner.
Something to watch for and correct when you run your simulations….If left unchecked, the busses
will tend to clump together and even pass each other in situations where there are not a lot of
busses in the system. This is a problem because busses that are clumped together will not serve
evenly the potential riders at some stops. You should check to see if clumping is happening. If it
is, try to incorporate something into the Bus class to keep a bus from getting to close to the bus
in front of it. In the real world, a bus will hang out at a stop if the driver can see another bus
CSCI 1933 PROJECT 4 WHAT TO DO
ahead of it less than two stops away. We recommend that you first determine whether clumping
is happening and prove it with some output from your simulator. Then, build in some code into
your Bus class to slow down busses that are getting too close to the bus ahead of it. Note that this
will only make sense when the number of busses is fewer than about one half the number of stops
in each direction.
The problem is purposely vague so that you can decide what statistics you need to gather and
what simulation tests you should run. But, you need to present enough information so that the
bus company can decide how many buses and what bus size it needs for various loads. (Keep in
mind that the bus company will want statistics for the busy times (lunch and rush hour) and well
as off-peak times such as weekends and nights. A significant portion of the grading will be based on
the write-up of your results which will include your simulation results presented in a useful format,
conclusions and recommendations. This means that you will need to have a working simulator in
order to have results to write about.
CSCI 1933 PROJECT 4 THE WRITE-UP
The write-up must be submitted as a .pdf document along with the rest of your source code. 25%
of your project grade will be somehow connected to the write-up. When deciding on statistics to
maintain and the simulations to run, think about the need to support your conclusions in your
write-up. The write-up should be in the form of a report–such as a consulting report–that you
might submit to the bus company. The report should include data (such as average travel time
and passenger miles per gallon) summarized in a concise and readable fashion along with specific
data that proves that the simulation results are correct. Please be sure that the report is concise.
For example, do the numbers make sense? Are your simulation runs at equilibrium? (That is,
as you run the same model with the same parameters for longer times, do the stats tend to stay
constant?) Certainly, some statistics are more difficult to properly calculate than others. So, don’t
try to do it all at once. Get some stats going, and verify them, before moving on.
In order for this to be a successful project, you need to start NOW, and have your simulator working
about 5-7 days before the project is due. That will give you enough time to run all the tests, make
modifications and produce the report. Remember, the bus company will be interested in how many
buses and what size buses they will need for various loads, average number of passengers at each
stop, the average and maximum passenger wait times, and average travel time. You will need to
run your simulation multiple times. It will take some thinking to know what runs to make, how to
effectively present your findings and deal with, or account for, bus clumping and passing.
CSCI 1933 PROJECT 4 THE README
A common expectation of large software projects is that they provide a readme file to familiarize
the user with the project. You must provide a readme file along with your project; it needs to
contain (at-least) the following items, which are often included in readme files for other projects:
• The project name and author information.
• Instructions for running your project on a new machine.
• An overview of the project organization and hierarchy.
• The data structures and algorithms used in the project, and why they are a good choice.
• Any known bugs or issues associated with the project.
As this project is largely left up to student design, the intent of this readme file is to familiarize
your TAs with your project. A good readme file will make grading the project easier, and be the
capstone on your submission.