The large rectangular signs along a highway showing route numbers, exit names and mile distances all share one background colour. What is it, and what does it signal?

Why D is correct

Green is the colour of the guidance family: route confirmations, destination distances, exit names and junction advance signs. Guidance signs are the map layer of the roadside — they tell you where you are and how to get where you are going, without commanding or warning anything. The colour matters operationally because it tells your eye what kind of information a sign carries before the words resolve: at highway speed, green means it is safe to read at leisure, whereas yellow means the content is a hazard you must act on now.

Why the other options are wrong

A. White, marking regulatory route assignments

White carries regulatory instructions — limits, turns, lane assignments. Route numbers appear on white route markers at intersections, but the big green highway panels are guidance, and the distinction between instruction and information is carried entirely by the colour.

B. Blue, marking services available at the exit

Blue identifies services at an exit — fuel, food, lodging — not the route and distance structure. Both are informational, but the split is deliberate: green gets you there, blue tells you what is there.

C. Yellow, marking navigational hazards ahead

Yellow is reserved for warnings, which demand immediate attention and action. Distance and route information is precisely the category of content that must not wear a warning colour, or every sign on the highway would trigger the same alert.

On the road

Forty minutes of interstate monotony, and the green panel slides into view: your exit, two miles, followed by the countdown markers. Nothing about it demands a reaction — it is pure planning material, which is why you can absorb it in a glance and keep your attention on the road. That unhurried quality is exactly what the green background guarantees.

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