Stats Test

A research firm tracks the average highway speed of 30 drivers driving home on Day 1. For the next 10 days, the drivers are given two cups of coffee 1 hour before the drive home. On the 10th day, the average highway speed is measured again. Does this study involve dependent or independent samples? You are interested in knowing if there is a statistical difference in driving speeds between Day 1 and Day 10. Which statistical test would be appropriate? Why?