The equation \( Y = 7X \) indicates a direct proportional relationship between the number of road projects \( X \) and the time (in weeks) \( Y \) it takes to complete those projects.
In this context, the constant of proportionality is 7, which means that for each road project, it takes the crew 7 weeks to complete it. Therefore, the correct interpretation is:
D: the constant of proportionality is seven; it takes the crew of workers 7 weeks to complete one road project.
This means if they have 1 road project, it takes 7 weeks. If they have 2 projects, it takes 14 weeks, and so forth, following the relationship described by the equation.