Which is better? A four-way stop or a roundabout?

https://www.youtube.com/watch?v=BvNO8LWVfAg

In a MythBusters episode, the question was asked, "Which is better? A four-way stop or a roundabout?" "Better" was determined based on determining the number of vehicles that travel through the four-way stop over a 5-minute interval of time. Suppose the folks at MythBusters conducted this experiment 15 times for each intersection design.

(a) What is the variable of interest in this study? Is it qualitative or quantitative?

(b) Explain why the data might be analyzed by comparing two independent means. Include in this explanation what the null and alternative hypotheses would be and what each mean represents.

(c) A potential improvement on the experimental design might be to identify 15 groups of different drivers and ask each group to drive through each intersection design for the 5- minute time interval. Explain why this is a better design and explain the role randomization would play. What would be the null and alternative hypotheses here and how would the mean be computed?