Case Study - Speedy Tires
Salem, the Transport Manager at Speedy Tires, has just returned from a meeting with the Managing Director. Apparently the police received complaints from local residents about the parking of heavy trucks in the side streets near the factory. This is occurring because there is insufficient room in the depot for trucks to wait to be loaded/unloaded.
To reduce the congestion it has been suggested a second bay be built. However, before this is done a simulation of the current system is to be developed and you have been asked to take on this project.
Your first task was a data collection exercise, and this gave you the following information:
(i) The depot is open from 08:00 to 18:00 Sundays to Thursdays.
(ii) Trucks require either loading or unloading (not both).
|
Type of Service
|
Frequency (%)
|
|
Loading
|
70
|
|
Unloading
|
30
|
(iii) The frequency distribution of the loading/unloading operations found by timing a large number of trucks were shown in the following tables.
|
Loading Time (min)
|
Frequency (%)
|
|
0 to under 30
|
20
|
|
30 to under 40
|
35
|
|
40 to under 50
|
22
|
|
50 to under 60
|
15
|
|
60 to under 70
|
8
|
|
Unloading Time (min)
|
Frequency (%)
|
|
0 to under 30
|
30
|
|
30 to under 40
|
40
|
|
40 to under 50
|
25
|
|
50 to under 60
|
4
|
|
60 to under 70
|
1
|
The frequency distribution of the inter-arrival time; that is, the time between successive arrivals, was shown in the following table.
|
Inter-arrival Time (min)
|
Frequency (%)
|
|
0 to under 10
|
15
|
|
10 to under 20
|
40
|
|
20 to under 30
|
30
|
|
30 to under 40
|
5
|
|
40 to under 50
|
5
|
|
50 to under 60
|
3
|
|
60 to under 70
|
2
|
You have also made the following assumptions:
(i) A second bay would be used like the first, that is, loading and unloading.
(ii) A single queue of trucks would form and a truck could use either bay on a first-come, first-served basis.
Required:
1. Explain why simulation is a better method than experimenting on the real system for this problem.
2. Using the random numbers which will be e-mailed to each group separately, manually simulate the depot operations with one bay and find the average waiting time of the 10 trucks?
3. Repeat the simulation using 2 bays.