One portion of the research described in a paper by Yean-Jye Lu5 involved an evaluation of maneuver times for vehicles of various sizes that were involved in making a left turn at an intersection with a separate left-turn lane but without a separate left-turn phase on the traffic light governing the intersection (an "unprotected" left-turn maneuver). The maneuver time was measured from the instant that a vehicle entered the opposing lanes of traffic until it completely cleared the intersection. Four-cylinder automobiles were classified as "small cars" and sixor eight-cylinder automobiles as "large cars." Trucks and buses were combined to form a third category identified as "truck or bus." Other motorized vehicles (motorcycles, etc.) were ignored in the study. A summary of the data, giving maneuver times (in seconds) for vehicles that attempted the left-turn maneuver from a standing stop, appears in the accompanying table.
|
Vehicle Type
|
Sample Size
|
Mean
|
Standard Deviation
|
|
Small car
|
45
|
459
|
0.70
|
|
Large car
|
102
|
4.88
|
0.64
|
|
Truck or bus
|
IS
|
6.24
|
0.90
|
a. Is there sufficient evidence to claim that the mean maneuver times differ for the three vehicle types? Give bounds for the attained significance level.
b. Indicate the appropriate conclusion for an α =.05 level test.