Taylor lets Luke know that he is getting a traffic light installed in Stars Hollow, even though there hasn’t been an accident in ten years (he apparently has powers to make decisions unilaterally in the town’s best interests when it comes to public safety).
As usual, Taylor is all about town progress, while Luke is all about keeping Stars Hollow exactly the way it has been – two different ways they show their love for the town. Their struggles and interactions end up giving Stars Hollow better outcomes; without Luke, the town would change too much and lose its character, while without Taylor it would stagnate and become a backwater.
This traffic light is the one alluded to in the episode’s title.
The Annotated Gilmore Girls 