A driver holds exactly the posted 45 mph limit through a heavy snowstorm in which visibility has dropped to half a block. Which statement is correct?

Why B is correct

Posted limits describe a maximum under good conditions, not an entitlement. Every jurisdiction also carries a basic rule requiring drivers to travel at a speed reasonable and prudent for what is actually in front of them, and that rule takes over the moment conditions degrade. The reason is mechanical rather than moral: at that visibility the distance needed to stop exceeds the distance within which the driver can see anything worth stopping for. Snow removes grip and multiplies braking distance at the same time it removes sight distance. A driver cited for driving too fast for conditions was very often driving at or below the posted number.

Why the other options are wrong

A. Perfectly legal, because the posted limit is the only speed rule there is

Treating the posted limit as the sole rule mistakes a ceiling for a target. The number is set assuming dry pavement, daylight and clear sight lines, none of which hold in a storm.

C. Required, since going slower would obstruct the traffic behind

Following traffic has no claim on your speed. Obstruction rules exist for drivers who block a clear road, not for those slowing because the road itself has become dangerous.

D. Acceptable until something actually gets hit

Waiting for a collision reverses how enforcement actually works. The violation is the speed given the conditions; whether a crash occurs only decides what the paperwork says.

On the road

Visibility is about 100 metres. Stopping distance on packed snow at 45 mph is comfortably more. The driver sees the stopped car and grasps instantly what their speed means — but they had a choice several seconds earlier and now they have physics.

Similar questions

• Below the Interstate Minimum Speed | CO

  A minimum speed is posted on the interstate you have just joined, but a mechanical fault means your car cannot sustain it. What is the right response?

• Overdriving Your Headlights | CO

  You are driving an unlit rural road at night on low beam. What does the term 'overdriving your headlights' mean?

• Double the Speed, Quadruple the Stop | CO

  A driver doubles their speed from 30 mph to 60 mph on the same dry stretch of road. What happens to the distance required to stop?

• Slowing for Junctions and Crossings | CO

  Beyond curves and hills, which additional locations require a driver to reduce speed even where no lower limit is posted?

• Keeping Pace With Moving Traffic | CO

  Crash research repeatedly links highway collisions to speed differences between vehicles rather than to absolute speed. What practical choice follows from that?