Miles per hour

World Map of Speed Limit Units on Traffic Signs

UK 50 mph speed limit sign

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2014-08-19 11 59 11 Speed limit 65 miles per hour sign along northbound Nevada State Route 225 (Mountain City Highway) about 10.9 miles north of Nevada State Route 535 (Idaho Street) in Elko County, Nevada

Miles per hour (mph) is a unit of speed or velocity in both US customary units as well as the Imperial system. It expresses the number of miles traveled in an hour. The unit is commonly used in the United States, the United Kingdom, and some other countries where the imperial system is either currently used or was used in the past. It is most commonly applied to road traffic speeds, but it is also used in various other contexts such as in the aviation and maritime sectors.

Usage

In countries where the metric system is used for most purposes, road traffic speeds are usually given in kilometers per hour (km/h). However, the United Kingdom and the United States are notable exceptions, with road speeds typically indicated in miles per hour. This unit is also used in some other countries, such as the Bahamas, Antigua, and Barbuda, and is sometimes found in literature or older publications in Canada.

Conversion

The conversion between miles per hour and kilometers per hour is straightforward. One mile per hour is approximately equal to 1.60934 kilometers per hour. Conversely, one kilometer per hour is equivalent to about 0.621371 miles per hour. These conversion factors are essential for understanding and comparing speeds in countries that use different measurement systems.

Calculation

The calculation of speed in miles per hour is a simple ratio of distance to time. It can be represented by the formula:

\[ \text{mph} = \frac{\text{miles}}{\text{hours}} \]

For example, if a vehicle travels 60 miles in one hour, its speed is 60 mph.

Historical Context

The use of miles per hour as a unit of speed has a long history, closely tied to the use of the imperial system of measurement. The unit has been used in transportation and navigation for centuries, reflecting the significant influence of British maritime and industrial practices globally. With the advent of motor vehicles, miles per hour became an essential unit for expressing vehicle speeds, particularly in countries with strong historical ties to the British Empire.

Legal and Safety Implications

Speed limits are typically set in miles per hour in countries that use this measurement. These limits are enforced to ensure road safety, taking into account the design of the road, traffic conditions, and the urban or rural setting. Exceeding these speed limits can result in legal penalties, including fines, license points, or even imprisonment for severe offenses.

Controversies and Challenges

The use of miles per hour in countries predominantly using the metric system for other measurements sometimes leads to confusion and calls for standardization to kilometers per hour. Advocates for this change argue that it would simplify calculations, reduce confusion for international travelers, and align with global standards. However, resistance to such changes often stems from tradition, the cost of changing road signage, and the need to update legal documents and vehicle speedometers.

See Also

• Speed
• Kilometers per hour
• Imperial system
• US customary units
• Speed limit

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