Quentin and his friends pass through the construction zone, where it is impossible to drive faster than 35 miles per hour. Lacey requests an unscheduled stop so she can use the bathroom. They find a gas station, and Quentin volunteers to take over driving. It seems only fair, since tracking Margo is his personal mission. Lacey allows Quentin to take the wheel, and lies down in the back.
Quentin feels a personal responsibility for this trip, and recognizes that his friends are there for his purposes, rather than their own. It is interesting how this mirrors the car trip he went on with Margo at the beginning of the novel, when he was there for her rather than for himself. Now, Quentin puts Lacey above himself by volunteering to drive, just as she puts him above herself by volunteering to come with him on the trip.