Final answer:
A speed limit sign indicates the maximum legal speed in ideal conditions, balancing safe travel with practical law enforcement. Differences between a vehicle's speedometer reading and the de facto speed limit can give a small buffer before a ticket is issued. Speed limits can also be converted between different units of measurement.
Step-by-step explanation:
A speed limit sign tells you the maximum speed allowed in ideal conditions. This means that the speed displayed is considered the safest upper speed that traffic law allows for vehicles to travel in optimal weather and road conditions. It's important to understand that even if your vehicle's speedometer shows a slightly higher speed than the limit, such as driving 31 miles per hour in a 30-mph zone, you might not necessarily be in trouble due to a margin of error in speedometer readings and law enforcement practices. However, exceeding the limit to a greater extent can result in a traffic ticket.
The concept of de jure speed limits, which are the legal speed limits posted on signs, is different from de facto speed limits, which may reflect the threshold at which police officers typically enforce the regulation. The de facto speed limit can thus be a bit above the posted limit, recognizing small inaccuracies in speedometer measurements and providing a cushion before law enforcement action is taken.
Physical quantities and units, such as speed limits, can be converted between different measurement systems. For instance, a speed limit of 100 km/h on some interstates can be converted to approximately 62 miles per hour or 27.78 meters per second.