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DMV Permit · Speed Limits

What is the minimum speed law on most US highways?

Reviewed by Jordan Morley, Editorial Lead at 247SimpleTests. Written by the 247SimpleTests Editorial Team from the official source material cited on every question.

Correct answer

Most state laws require driving at a 'reasonable speed for conditions' — slow drivers (often 20+ mph below the limit) can be cited for impeding traffic if they have no good reason

  1. A 20 mph below the maximum
  2. B Half the posted maximum
  3. C Most state laws require driving at a 'reasonable speed for conditions' — slow drivers (often 20+ mph below the limit) can be cited for impeding traffic if they have no good reason
  4. D There is no minimum

Why this is the answer

Most US highways do not have a posted minimum speed but state laws generally require driving at a reasonable speed for conditions and prohibit impeding traffic without good cause. Some Interstates post a minimum speed (typically 40-45 mph) for vehicles that cannot maintain prevailing traffic speeds. A driver going significantly below the prevailing speed (often defined as 20+ mph below the limit) can be cited for impeding traffic. Slow drivers, especially in the left lane, create dangerous speed differentials with other traffic. If you cannot maintain reasonable speed (vehicle problems, towing, learner driver), use the right lane and consider using a route below highway grade.
Source: State driver handbooks, Slow Driving

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About this topic: Speed Limits

Speed limit questions cover the default limits in school zones, residential areas, business districts and highways, the basic speed rule (never faster than conditions allow) and how to adjust speed for weather and traffic. This is one of 11 Rules of the Road questions on speed limits, each with a full explanation on a single study page.

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