Information AboutSpeed Limit |
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A road speed limit is the maximum speed allowed by Law for Road Vehicle s. Speed limits are commonly set and enforced by the Legislative Bodies of nations or provincial governments, such as countries within the world. In addition to setting a maximum speed limit, most governments also enforce speed limits which are relative to the driving conditions experienced; that is, drivers should adjust their maximum speed when driving in Fog , Heavy Rain , or other similar conditions. For example, the California Civil Code 22350 states that "No person shall drive a vehicle upon a highway at a speed greater than is reasonable... and in no event at a speed which endangers the safety of persons or property." This "basic rule", or similar legal language, applies even where no maximum speed limit is in place (such as formerly in the U.S. state of Montana ). Some roads also have "minimum speed limits", where slow speeds are considered to impede traffic flow or be dangerous. The first speed limit was the limit introduced by the Locomotive Act of 1861 (or "Red Flag Act") in the United Kingdom (automobiles were in those days termed “light locomotives”). In 1865, the revised Locomotive Act reduced the speed limit to in the country and in towns. The 1865 Act required a man with a red flag or lantern to walk ahead of each vehicle, enforce a walking pace, and warn horse riders and horse drawn traffic of the approach of a self-propelled machine. The replacement of the "Red Flag Act" by the Locomotive Act of 1896, and the increase of the speed limit to has been commemorated each year since 1927 by the London To Brighton Veteran Car Run . Nepal , the Isle Of Man and the Indian states of Uttar Pradesh and Kerala are the only places in the world that do not have a general speed limit. In Germany, some (but not all) sections of the autobahn ( Motorway ) network also remain free from speed limits. Not including public roads which do not have a legal speed limit, the highest speed limit in the world is 160 Km/h (99 Mph ), which has been experimentally applied on selected test stretches in Austria and the United Arab Emirates . {Link without Title} FACTORS IN SETTING SPEED LIMITS Speed limits are set based on many factors, such as road features, crash records, legal statutes, administrative judgment, engineering judgment and political dictate. Two common measures for setting speed limits are the design speed of the road and the 85th percentile of travel speeds (See Design Speed, Operating Speed, and Posted Speed Practices ). Fuel efficiency also affects the choice of speed limits. United States at one time had attempted a maximum speed limit of 55 mph to reduce fuel consumption (See National Maximum Speed Law ). It is also estimated that speed limits can be used to reduce emissions and pollution, and some areas have reduced speed limits for improving the air quality (See Environmental Speed Limits ). Design speed Definition In the United States the design speed is officially defined as "a selected speed used to determine the various geometric design features of the roadway", according to the 2001 American Association Of State Highway And Transportation Officials highway design manual, commonly referred to as the "Green Book." Previous versions of the Green Book referred to design speed as the "maximum safe speed that can be maintained over a specific section of highway when conditions are so favorable that the design features of the highway govern"; however the 2001 edition removed the term "safe" in order to avoid the implication that speeds greater than the design speed were necessarily "unsafe." Limitations Safe operating speeds can exceed the design speed. Example reasons include: #A design speed is not a representative speed of an entire roadway. Rather, the road's design speed is limited by its most restrictive feature, such as a curve, bottleneck, or hill. #Actual roadway design may exceed the design specifications. #Current parameters for determining the design speed assumes the capacity of outdated automotive technology. #The stated design speed for a given road is usually not changed. Therefore, the design speed on older roads, which were calculated with older methodologies, may not factor in improved automotive technology which can maintain designed safety at higher travel speeds. In commonly accepted engineering practice, design speed is considered a "first guess" at an appropriate speed limit. 85th percentile rule In the United States, traffic engineers may rely on the 85th percentile rulehttp://www.ite.org/standards/speed_zoning.pdf to establish speed limits. The speed limit should be set to the speed that separates the bottom 85% of vehicle speeds from the top 15%. The 85th percentile is slightly greater than a speed that is one Standard Deviation above the mean of a Normal Distribution . The theory is that traffic laws that reflect the behavior of the majority of motorists may have better compliance than laws that arbitrarily criminalize the majority of motorists and encourage violations. The latter kinds of laws lack public support and often fail to bring about desirable changes in driving behavior. An example is the federally-mandated 55 mph (90 km/h) speed limit that was removed in part because of notoriously low compliance. Most U.S. jurisdictions report using the 85th percentile speed as the basis for their speed limits, so the 85th-percentile speed and speed limits should be closely matched. However, a review of available speed studies demonstrates that the posted speed limit is almost always set well below the 85th-percentile speed by as much as 8 to 12 mph (see p.88) (13 to 19 km/h). Some reasons for this include:
SIGNAGE For more information about traffic signs in general, see Traffic Sign . , showing a 60 km/h (60 mph in the UK) restriction]] National Speed Limit Roadsign .]] The start of a speed limit is usually marked with a speed limit Traffic Sign . Speed limit signs can appear near Border s and road intersections, and in some cases speed limit reminder signs appear at regular intervals. In the European Union , large signposts showing the national speed limits of the respective country are usually erected immediately after Border Crossing s, with a repeater sign some 200 to 500 metres (about 650 to 1,650 ft) after the first sign. The same practice is followed in several U.S. State s. Occasionally, different units of speed measurement are used on each side of a border. For example, Northern Ireland (part of the UK ) uses miles per hour (mph) for speed limits and miles for distance, whereas the Republic Of Ireland uses kilometres per hour (km/h) for speed limits and kilometres for distance. The UK and the United States are the only major nations still using the customary (imperial) units system. The U.S. has shown no intention to convert to SI units, and reverted to imperial units in states that had both imperial and SI systems such as California and Arizona. However, Ohio, South Dakota, Rhode Island, and Vermont (especially near the Canadian border) still have some SI distances and speeds on their exit distance and speed limit signs (such as / 110 km/h, or 3 miles / 5 km to next exit). When entering Canada, signs are posted reminding drivers to use metric signage. Conversely upon entering the US from Canada (at least in Vermont), drivers are shown a 100 km/h speed limit sign. All exit distance signs on Interstates in New Hampshire are marked with the distance in miles followed by the distance in kilometres shown in parentheses. Houston, Texas has some signs in both imperial and SI units near its airports and downtown. Delaware Route 1 and Interstate 19 have exits numbered by kilometer - I-19 also has kilometer posts. Design of speed limit signage varies between countries. In the European Union, the red circle is most common, while in North America, signs are usually rectangular. Australian speed limit signs are a combination, with a red circle inside a rectangular sign. Sometimes, speed limits are also painted on the road surface as a reminder. The design of minimum speed signage also varies between countries. Most countries use blue circles based on obligatory signs. A Japanese minimum speed sign has the same design as a maximum speed sign but with a horizontal line below the number. |
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