Transportation agencies post speed limits after studying a road's design, its crash history and the speeds most drivers already choose. What does that process imply about the number on the sign?

Why D is correct

A posted limit is the product of engineering judgement about a road under normal conditions — alignment, sight lines, intersections, how traffic actually behaves. It is a ceiling calibrated to the road, not a certification that the road is safe at that speed today. That is why the basic speed rule survives every sign: you must drive a speed that is reasonable for the actual conditions, which can be lawful above a minimum and still reckless, or lawful under a maximum and still too fast for ice, fog, rain or a blocked lane. The sign and the conditions are separate tests, and both bind.

Why the other options are wrong

A. The limit is a promise that the posted speed is always safe in all conditions

No number survives contact with black ice, fog or a stalled car in the lane. The engineering study behind the sign assumes ordinary conditions precisely so that the basic rule can govern the extraordinary ones.

B. The limit is a minimum standard you are expected to approach whenever possible

Treating a ceiling as a target inverts its meaning. The limit is the outer boundary of what the road's design tolerates under good conditions, not a quota for enthusiastic drivers.

C. The limit is set primarily to generate enforcement revenue

Revenue is a byproduct that enforcement discussions never stop arguing about, but the number itself comes from road and traffic studies. The engineering basis is published and auditable in a way a revenue target would not need to be.

On the road

A canyon two-lane posts 45 through a section you have driven a hundred times — in July. In October, with the first freeze glazing the shaded bends, the same legal 45 would be absurd, and the driver who takes the curve at it finds out on the slick side of physics. The sign has not changed; the road underneath it has, and the basic rule was always the one that mattered.

Similar questions

• Coasting in Neutral | CO

  On a long descent, a driver shifts into neutral to coast and save fuel. Why is this regarded as poor and unsafe practice?

• Impeding Traffic | CO

  You are comfortable cruising at 40 in the right lane of a 65 mph freeway on a clear day with light traffic, and cars are stacking up behind you. What does the law say about driving so slowly that you disrupt the normal flow?

• Speed Within Your Sight Distance | CO

  You are driving on a rural road at the posted limit when a fog bank cuts your view ahead to a few car lengths. What principle governs how fast you should now be going?

• School Zone Rules: Slow Down and Obey Guards

  You are driving through a school zone during arrival time with children walking nearby. What does the law require of you?

• Work Zones: Driving Past Workers Safely | CO

  You enter a work zone where workers are standing beside the travel lane and the lanes have been narrowed. How should you drive?