Why Some Speed Limits Are Set at 21mph Instead of 20mph

Speed limits can often be a source of confusion, especially when they are set at specific intervals that aren’t immediately obvious. One such example is the speed limit in New Hampshire, where you might notice that some signs state 21 mph rather than 20 mph. This article aims to clarify the reasoning behind this and shed light on the legal and practical considerations involved in setting such limits.

Background on Speed Limits in New Hampshire

Speed limits in New Hampshire follow a pattern where the number always ends in 0 or 5. This can make it seem logical that 20 mph would be the typical limit for certain areas. However, the system of fines and enforcement has an interesting quirk. Fines are levied based on specific tiers, one of which is any speed 21 mph or more over the limit. For speed limits under 55 mph, the tier is for speeds 21-25 mph over the limit. This means that legally, a speed limit of 20 mph is set with the understanding that exceeding it by 21 mph would warrant a fine.

Legal and Enforcement Perspective

From a legal standpoint, the difference between 20 mph and 21 mph becomes a matter of interpretation. For a physicist, "20" would indeed mean "less than 21" due to the precision of measurements. For a law abiding driver, a speed of 20 mph means no more – a threshold that must be adhered to. By setting the limit at 21 mph, the intention may be to mildly relax the threshold, although the exact rationale behind this is not always clear.

Similarity with Other Legal Standards

A similar scenario can be observed in equestrian sports, specifically in dressage competitions. The standard fence height is 30 cm. The rule often states that if the fence is "at least 30 cm," a penalty applies. However, factors such as fence sag or slight bends in the dirt can make the actual height vary. In such cases, judges must measure the fence at multiple points to determine if the penalty applies. For instance, if the fence is measured at 28 cm at one point, no penalty is imposed. If the rule had been set as "more than 25 cm," the situation would be much clearer, simplifying enforcement.

Importance of Clear and Consistent Rules

These examples highlight the importance of clear and consistent rules in both legal and practical contexts. Ambiguous rules can lead to disputes and complications in enforcement. Ill-thought-out rules may result in confusion and inconsistent outcomes. By aligning rules more logically and clearly, it makes it easier to enforce and reduce the likelihood of misunderstandings and disputes.

Conclusion

The use of 21 mph instead of 20 mph in speed limits is a result of the tiers in the system of fines and enforcement. This system is designed to create a clear boundary between legal and illegal speeds, ensuring fair and consistent enforcement. Similarly, in other contexts, such as equestrian sports, clear and unambiguous rules enhance clarity and consistency. These examples demonstrate the value of precision and clarity in legal and practical standards.