In the hope of attracting more riders, a city transit company plans to have express bus service from a suburban terminal to the downtown business district. These buses should save travel time. The city decides to perform a study of the effect of four different plans (such as a special bus lane and traffic signal progression) on the travel time for the buses. Travel times (in minutes) are measured for several weekdays during a morning rush-hour trip while each plan is in effect. The results are recorded in the following table.
| Plan |
| 1 |
2 |
3 |
4 |
| 27 |
25 |
34 |
30 |
| 25 |
28 |
29 |
33 |
| 29 |
30 |
32 |
31 |
| 26 |
27 |
31 |
|
|
24 |
36 |
|
a What type of experimental design was employed?
b Is there evidence of a difference in the mean travel times for the four plans? Use α = 0.01.
c Form a 95% confidence interval for the difference between plan 1 (express lane) and plan 3 (a control: no special travel arrangements).