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139-424: In legal terminology, the assured clear distance ahead ( ACDA ) is the distance ahead of any terrestrial locomotive device such as a land vehicle , typically an automobile , or watercraft , within which they should be able to bring the device to a halt. It is one of the most fundamental principles governing ordinary care and the duty of care for all methods of conveyance, and is frequently used to determine if

278-400: A i while through traffic travels a distance equal to their speed multiplied by that time. The time t pc , for the stopped motorist, is the sum of perception time and the time required to actuate an automatic transmission or shift to first gear which is usually between 1 ⁄ 2 to one second. Horizontal clearance is measured from the edge of the traveled way to the bottom of

417-500: A Built-up area (BUA) as an area of built-up land of at least 20 hectares (0.077 sq mi), separated from other settlements by at least 200 metres (660 ft). For 2011 census data there are 5,493 built-up areas, of which 501 are divided into Built-up area sub-divisions (BUASD) for which data is also available. Each built-up area is named algorithmically, using Ordnance Survey place-name data. The ONS has produced census results from urban areas since 1951, since 1981 based upon

556-660: A Department of the Environment, Transport and the Regions survey in October 2000): Urban areas Urban areas originate through urbanization , and researchers categorize them as cities, towns, conurbations or suburbs . In urbanism , the term "urban area" contrasts to rural areas such as villages and hamlets ; in urban sociology or urban anthropology it contrasts with natural environment . The development of earlier predecessors of modern urban areas during

695-465: A passport and visa . Tours are a common type of travel. Examples of travel tours are expedition cruises, small group tours, and river cruises. Authorities emphasize the importance of taking precautions to ensure travel safety . When traveling abroad, the odds favor a safe and incident-free trip, however, travelers can be subject to difficulties, crime and violence. Some safety considerations include being aware of one's surroundings, avoiding being

834-399: A two-second rule or three-second rule. See Table of 2-second following distances In the fifth case, critical speed V cs applies when road curvature is the factor limiting safe speed. A vehicle which exceeds this speed will slide out of its lane. Critical speed is a function of curve radius r , superelevation or banking e , and friction coefficient μ ; the constant g again

973-480: A building at least every 200 m (660 ft) and at least 200 people. To be considered a town or a city ( kaupunki ) for statistical purposes, an urban area must have at least 15,000 people. This is not to be confused with the city / town designation used by municipalities . In France , an urban area ( Fr: aire d'attraction d'une ville ) is a zone encompassing an area of built-up growth (called an "urban unit" ( unité urbaine ) – close in definition to

1112-762: A citable driving offense, thus burdening an offending driver to rebut a presumption of negligence . States with such explicit ACDA standard of care provisions include: Iowa, Michigan, Ohio, Oklahoma, Pennsylvania, and Texas. States which apply the principle by statute to watercraft on navigable waterways include all 174 member states of the International Maritime Organization , notwithstanding membership: Great Britain and its common law inheriting Commonwealth of Nations , The United States, Florida, Hawaii, Illinois, Louisiana, Michigan, Montana, Oregon, Texas, and West Virginia. Most state-issued and some Canadian driver handbooks instruct or mention

1251-446: A close vehicle in front. This maximum velocity is denoted by the case variable V A C D A s {\displaystyle V_{ACDA_{s}}} , the friction coefficient is symbolized by μ {\displaystyle \mu } —and itself a function of the tire type and road conditions , the distance d A C D A s {\displaystyle d_{ACDA_{s}}}

1390-653: A densely settled core created from census blocks and contiguous qualifying territory that together have at least 2,000 housing units or 5,000 persons." There were 2,646 urban areas identified by the Census Bureau for 2020. 511 of these had a population of 50,000 or more. For the 2000 and 2010 censuses, the Census Bureau differentiated between two kinds of urban areas: urbanized areas and urban clusters. The term urbanized area denoted an urban area of 50,000 or more people. Urban areas under 50,000 people were called urban clusters . Urbanized areas were first delineated in

1529-543: A density requirement of 4,000 inhabitants per square kilometre (10,000/sq mi). Seoul is the largest urban area in South Korea . For the Census of India 2011, the definition of urban area is a place having a minimum population of 5,000 of density 400 persons per square kilometre (1,000/sq mi) or higher, and 75% plus of the male working population employed in non-agricultural activities. Places administered by

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1668-525: A driver is in proper control and is a nearly universally implicit consideration in vehicular accident liability. The rule is a precautionary trivial burden required to avert the great probable gravity of precious life loss and momentous damage. Satisfying the ACDA rule is necessary but not sufficient to comply with the more generalized basic speed law , and accordingly, it may be used as both a layman's criterion and judicial test for courts to use in determining if

1807-407: A driver on an uncontrolled through street has a duty to slow down in crossing an intersection and permit controlled drivers to be able pass through the intersection without danger of collision. The driver on the through street must anticipate and hence not approach at an unsafe speed which would prevent another driver from being able to enter while traffic was some distance away, or would be unsafe to

1946-452: A driver who has already established control of the intersection under a prudent acceleration a i , from a stop at a limit line a distance d sl away. The pedantic fourth case applies when the dynamic ACDA "following distance" ( d ACDA d ) is less than the static ACDA "line-of-sight" distance ( d ACDA s ). A classic instance of this occurs when, from a visibility perspective, it would be safe to drive much faster were it not for

2085-465: A foreseeable dynamic hazard—such as to maintain a distance as to be able to safely swerve around a bicyclist should he succumb to a fall—without requiring a full stop beforehand, if doing so could be exercised with due care towards surrounding traffic. Quantitatively this distance is a function of the appropriate time gap and the operating speed: d ACDA =t gap ⋅ v . The assured clear distance ahead rule, rather than being subject to exceptions,

2224-471: A forest with many trees which all eventually fell. In this specific regard, jurisdictions which grant drivers the liberty to be fools from their own folly, are also condoning the collateral damage and life loss which is expected to occur. Moreover, modern life-entrusting consumers of driving services and driverless cars who suffer such caused injury are left without legal remedy for foreseeable outcome of imprudent speed; this in-turn unnecessarily transfers

2363-442: A hazard. Collisions generally only occur within one's assured clear distance ahead which are "unavoidable" to them such that they have zero comparative negligence including legal acts of god and abrupt unforeseeably wanton negligence by another party. Hazards which penetrate one's proximate edge of clear visibility and compromise their ACDA generally require evasive action. Drivers need not and are not required to precisely determine

2502-465: A higher safe speed than human driven vehicles for a given ACDA where computer perception-reaction times are nearly instantaneous. The Assured Clear Distance Ahead can be subjective to the baseline estimate of a reasonable person or be predetermined by law. For example, whether one should have reasonably foreseen that a road was not assuredly clear past 75–100 meters because of tractors or livestock which commonly emerge from encroaching blinding vegetation

2641-514: A large majority of the population, typically 75%, is not engaged in agriculture and/or fishing is sometimes used. Since 2000, China 's cities have expanded at an average rate of 10% annually. It is estimated that China's urban population will increase by 292 million people by 2050, when its cities will house a combined population of over one billion. The country's urbanization rate increased from 17.4% to 46.6% between 1978 and 2009. Between 150 and 200 million migrant workers work part-time in

2780-713: A long way in transportation since Christopher Columbus sailed to the New World from Spain in 1492, an expedition which took over 10 weeks to arrive at the final destination; to the 21st century when aircraft allows travel from Spain to the United States overnight. Travel in the Middle Ages offered hardships and challenges, though it was important to the economy and to society. The wholesale sector depended (for example) on merchants dealing with/through caravans or sea-voyagers, end-user retailing often demanded

2919-430: A margin of which beyond hazards may reasonably be expected to spontaneously appear. The rule is the specific spatial case of the common law basic speed rule , and an application of volenti non fit injuria . The two-second rule may be the limiting factor governing the ACDA, when the speed of forward traffic is what limits the basic safe speed, and a primary hazard of collision could result from following any closer. As

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3058-406: A minimum of 20 hectares (200,000 m ; 49 acres). Any areas [separated by] less than 200 metres [of non-urban space] are linked to become a single built-up area. Argentina and Japan are countries where the urbanization rate is over 90% while Australia, Brazil, Canada, Chile, Mexico and the United States are countries where the urbanization rate is between 80% and 90%. There are two measures of

3197-403: A moose or a luxury car. Furthermore, modern times still provide no legal remedies for Darwinian misfortune upon the entire class of unwarnable accidents where drivers and their passengers would not have collided into the likes of a moose, livestock, fallen tree, rock, jetsam, horse-drawn vehicle, stalled vehicle, school bus, garbage truck, mail carrier, snowplow, washout, snow drift, or slid off

3336-572: A municipal corporation, cantonment board or notified town area committee are automatically considered urban areas. The Census of India 2011 also defined the term "urban agglomeration" as an integrated urban area consisting of a core town together with its "outgrowths" (contiguous suburbs). In Pakistan , an area is a major city and municipality if it has more than 100,000 inhabitants according to census results. Cities include adjacent cantonments . Urbanisation in Pakistan has increased since

3475-507: A number of large cities . The largest conurbation is the Rhine-Ruhr region (11 million in 2008 ), including Düsseldorf (the capital of North Rhine-Westphalia ), Cologne , Bonn , Dortmund , Essen , Duisburg , and Bochum . The Netherlands is the 30th-most densely populated country in the world, with 404.6 inhabitants per square kilometre (1,048/sq mi)—or 497 inhabitants per square kilometre (1,287/sq mi) if only

3614-427: A particular speed is negligent, but not to prove it is safe. As a spatial standard of care , it also serves as required explicit and fair notice of prohibited conduct so unsafe speed laws are not void for vagueness . The concept has transcended into accident reconstruction and engineering. This distance is typically both determined and constrained by the proximate edge of clear visibility, but it may be attenuated to

3753-641: A population centre remains unchanged from that of an urban area: a population of at least 1,000 people where the density is no fewer than 400 persons per km . Mexico is one of many countries where the urbanization rate is at least 80%. Mexico City , its capital, is the largest urban area in the country. In the United States , the Census Bureau defines urban areas and delineates urban area boundaries after each census. The Bureau defines an urban area as "a statistical geographic entity consisting of

3892-447: A result of this uncorrected vagueness, group behavior can often be in opposition to safe speed and still be governing a hazardous posted speed limit. By federal law, posted speed limits are generally within 5 mph of the 85th-percentile speed of free-flowing traffic. Functionality, this amounts to citizens "voting" a street's speed limit with their gas pedal from the influence of groupshift . As people generally follow explicit rules all

4031-703: A road must be designed and maintained such that there is not a chance of obstruction in one's lane beyond the proximate edge of clear visibility. A road's vertical profile must be assured to have such a curvature as not to hide hazards close behind its crests. Discretion for drivers and pedestrians to enter onto a potentially occupied lane from a side street must be assuredly eliminated such as with fences, merge lanes, or signalized access. There must also be an assurance of no opportunity for animals and debris to enter from side lots, and that there are continuous multi-hourly maintenance patrols performed. Furthermore, such road sections must be distinguished from other roads so that

4170-500: A road's inferred design speed. Collision liability has historically benefited the law profession by being cloaked as a mixture of fact and law, but with EDR's precisely preserving "a state of facts" often repeated with differing trial outcomes, collisions are less a question of fact, but of law. Electronic access to precise EDR data and rulings with new ideological modeling tools, can now expose judges as consistent political advocates for differing special road user interests. Furthermore,

4309-525: A roadway at over 30 mph (48 km/h). Wildlife will frequently transit across a road before a full stop is necessary, however collisions with large game are foreseeably lethal, and a driver generally has a duty not to harm his or her passengers. The foreseeable intercept speed or defectively designed horizontal sight distance may vary "reasonably" with judicial discretion . See Table of safe speed versus horizontal line-of-sight This third case regards safe speed around un-signalized intersections where

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4448-405: A slower-moving vehicle ahead. As such, the dynamic ACDA is governing the basic speed rule, because in maintaining this distance, one cannot drive at a faster speed than that matching the forward vehicle. The "time gap" t g or "time cushion" is the time required to travel the dynamic ACDA or "following distance" at the operating speed . Circumstances depending, this cushion might be manifested as

4587-408: A speed above which no reasonable minds might differ as to whether it is unsafe or that one could come to a stop within the full distance ahead. Drivers and law enforcement alike can apply elementary level arithmetic towards a rule of thumb to estimate minimal stopping distance in terms of how many seconds of travel ahead at their current speed. For speed " v " in miles per hour, this rule of thumb

4726-784: A standard with descriptive mathematics, much of which are used in reverse by road engineers when designing or re-engineering roads to a speed criteria—for which its users were expected to follow. The range of visibility of which is the de facto ACDA, is usually that distance before which an ordinary person can see small hazards—such as a traffic cone or buoy —with 20/20 vision . This distance may be attenuated by specific conditions such as atmospheric opacity , blinding glare , darkness, road design , and adjacent environmental hazards including civil and recreational activities, horse-drawn vehicle, ridden animal, livestock, deer, crossing traffic, and parked cars . The ACDA may also be somewhat attenuated on roads with lower functional classification . This

4865-521: A stop up to 20 mph is about 0.15g, with more than 0.3g being difficult to exceed. The distance " d i " is the sum of the measured limit line setback distance—which is typically regulated by a Manual on Uniform Traffic Control Devices , at often between 4 and 30 feet in the United States—and the crosswalk , parking lane , and road shoulder width. A vehicle accelerating from a stop travels this distance in time t i = √ 2d i ⁄

5004-399: A strict standard of care, delegation of such standard to a jury assumes the representativeness heuristic for twelve people to determine ordinary care representative of everyone while ignoring its insensitivity to sample size , which of course when applied to multiple cases involving identical situational circumstances results in many verdicts with opposing extreme views, which works against

5143-522: A substantive portion of the ACDA liability space into act of god , government claims , strict liability , or other findings from legal fiction which the justice system generally abhors. What modern times are changing is that one may assure the distance is clear ahead virtually through the Internet of Things , as smart cars connect to get information from smart highways or pass what they see ahead or measure to traffic behind. A fundamental corollary of

5282-409: A suburb of another urban area rather than as a self-contained urban entity, or is geographically remote from other urban communities. Accordingly, the new definition set out three distinct types of population centres: small (population 1,000 to 29,999), medium (population 30,000 to 99,999) and large (population 100,000 or greater). Despite the change in terminology, however, the demographic definition of

5421-417: A trajectory or firing solution in order to hit a target with repeated accuracy. During the earliest stages of learning how to drive , one develops a memory of when to start braking (how long it takes) from various speeds in order to stop at the limit line. While there may be a degree of variance of such skill in seasoned drivers, they generally do not have the discretion in engaging in a behavior such as driving

5560-547: Is 56.2% urbanized, with roughly one-quarter of the countries reported as greater than 80% urbanized. Data is taken from the U.S. Central Intelligence Agency World Factbook estimates from 2020. According to Demographia, these are the 202 largest urban areas in the world by population (as of 2023): The UN publishes data on cities, urban areas and rural areas, but relies almost entirely on national definitions of these areas. The UN principles and recommendations state that due to different characteristics of urban and rural areas across

5699-467: Is a prolific source of accidents. In the United States , there is no explicit road marking promising clear distance beyond line of sight in the Manual on Uniform Traffic Control Devices , although there are signs communicating " limited sight distance ", " hill blocks view ", " crossroad ahead ", and " freeway ends ". A partial solution to this challenge is to remove driver discretion in determining whether

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5838-493: Is an area with a population of at least 1,000 people where the density is no fewer than 400 persons per square kilometre (1,000/sq mi). If two or more urban areas are within 2 km (1.2 mi) of each other by road, they are merged into a single urban area, provided they do not cross census metropolitan area or census agglomeration boundaries. In the Canada 2011 Census , Statistics Canada redesignated urban areas with

5977-410: Is as follows: If this distance is greater than the ACDA, they need to decelerate. While most experienced drivers develop a broad intuition required by everyday braking, this rule of thumb can still benefit some to recalibrate expectations for rare hard braking, particularly from high speeds. Additional simple corrections can be made to compensate for the environment and driving ability. Read more about

6116-623: Is because the probability of spontaneous traffic increases proportionally to the density of road access points, and this density reduces the distance a person exercising ordinary care can be assured that a road will be clear; such reduction in the ACDA is readily apparent from the conditions, even when a specific access point or the traffic thereon is not. Furthermore, even though a through-driver may typically presume all traffic will stay assuredly clear when required by law, such driver may not take such presumption when circumstances provide actual knowledge under ordinary care that such traffic cannot obey

6255-421: Is considered to be rural by the Census Bureau. The largest urban area in the United States is that of New York City and its surrounding suburbs. The New York– Jersey City – Newark , NY–NJ urban area had a population of 19,426,449 as of 2020, while the larger metropolitan area had a population of 20,140,470, and the combined statistical area had a population of 23,582,649. The next five largest urban areas in

6394-686: Is divided into 5 regions for planning purposes by the URA, even though as a city state Singapore is defined as a single continuous urban area. It is further subdivided into 55 urban planning areas , which acts as the boundaries of planned towns within the country. In Vietnam , there are six types of urban areas: Bangkok is the largest urban area in Thailand . As in other Nordic countries , an urban area ( taajama in Finnish ) in Finland must have

6533-550: Is highly urbanized. The ten largest metropolitan areas account for half of the population, and fewer than one in ten live in rural areas. About 3 million people live in Buenos Aires City and the Greater Buenos Aires metropolitan area totals around 15 million, making it one of the largest urban areas in the world, with a population of 18 million all up. Córdoba has around 1.5 million people living in

6672-821: Is not really intended to apply beyond situations in which a vigilant ordinarily prudent person could or should anticipate. A common way to violate the dynamic ACDA is by tailgating . The most accurate way to determine the ACDA is to directly measure it. Whereas this is impractical, sight distance formulas can be used with less direct measurements as rough baseline estimates. The empirical assured clear distance ahead calculated with computer vision , range finding , traction control , and GIS , such as by properly programming computer hardware used in autonomous cars , can be recorded to later produce or color baseline ACDA and safe speed maps for accident investigation, traffic engineering, and show disparities between safe speed and 85th percentile "operating" speed. Self-driving cars may have

6811-435: Is often a requirement to obtain temporary auto insurance valid in the country being visited. It is also advisable to become oriented with the driving rules and regulations of destination countries. Wearing a seat belt is highly advisable for safety reasons; many countries have penalties for violating seatbelt laws . There are three main statistics which may be used to compare the safety of various forms of travel (based on

6950-401: Is on occasion dependent on societal experience within the locale. In certain urban environments, a straight, traffic-less, through-street may not necessarily be assuredly clear past the entrance of the nearest visually obstructed intersection as law. Within the assured clear distance ahead, there is certainty that travel will be free from obstruction which is exclusive of a failure to appreciate

7089-952: Is one of the most urbanised countries in the world, with more than 50% of the population residing in Australia's three biggest urban centres. Statistics New Zealand defines urban areas in New Zealand, which are independent of any administrative subdivisions and have no legal basis. There are four classes of urban area: major urban areas (population 100,000+), large urban areas (population 30,000–99,999), medium urban areas (population 10,000–29,999) and small urban areas (population 1,000–9,999). As of 2021, there are 7 major urban areas, 13 large urban areas, 22 medium urban areas and 136 small urban areas. Urban areas are reclassified after each New Zealand census , so population changes between censuses does not change an urban area's classification. According to Statistics Canada , an urban area in Canada

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7228-431: Is otherwise reached. Steering control is independent from any concept of clear distance ahead. If a vehicle cannot be controlled so as to safely remain within its lane above a certain speed and circumstance, then it is irrelevant how assuredly clear the distance is ahead. Using the example of the previous case, the safe speed on a curve may be such that a driver experiences a lateral acceleration of less than 0.3g despite that

7367-466: Is prohibited, and people of ordinary intelligence can apply their braking experience or the seconds of distance to stop rule to the distance they can see; once one is allowed to cruise-on without control beyond the edge of visibility, there is little consensus on what arbitrary speed is unsafe, or what to assume of the vague conditions there-past. To be able to guarantee "assurance" beyond proximate edge of clear visibility, in doing so exempting ACDA duty,

7506-408: Is than an accident which would not have occurred except for the action or inaction of some person or entity contrary to a duty such as the exercise of proper care was the result of negligence . The liability space from which one can recover is typically, themselves, other parties, or nobody. Jurisdictional exceptions permitting one to legally take "assurance" that the distance will be clear beyond

7645-449: Is the acceleration of gravity. However, most motorists will not tolerate a lateral acceleration exceeding 0.3g ( μ  = 0.3) above which many will panic. Hence, critical speed may not resemble loss of control speed. Attenuated "side" friction coefficients are often used for computing critical speed. The formula is frequently approximated without the denominator for low angle banking which may be suitable for nearly all situations except

7784-506: Is the largest city by population and area, with a population of 19.10 million. In Bangladesh , there are total 11 City Corporations and 329 Municipal Corporations and 203 Small towns , which serves as the center for Upazilas . According to 2011 population census, Bangladesh has an urban population of 28%, with a growth rate of 2.8%. At this growth rate, it is estimated that the urban population of Bangladesh will reach 79 million or 42% of total population by 2035. In 2020, 54 percent of

7923-750: Is the maximum speed at which a vehicle can come to a full stop before an object, with speed V i , can intercept after having emerged and traveled across the horizontal sight distance "d hsd ". Urban and residential areas have horizontal sight distances that tend to be closely obstructed by parked cars, utility poles, street furnishing, fencing, signage, and landscaping, but have slower intercepting speeds of children, pedestrians, backing cars, and domestic animals. These interceptors combined with dense usage results in collisions that are more probable and much more likely to inflict harm to an outside human life. In rural areas, swift-moving spooked wildlife such as deer , elk , moose , and antelope are more likely to intercept

8062-452: Is the movement of people between distant geographical locations . Travel can be done by foot , bicycle , automobile , train , boat , bus , airplane , ship or other means, with or without luggage , and can be one way or round trip. Travel can also include relatively short stays between successive movements, as in the case of tourism . The origin of the word "travel" is most likely lost to history. The term "travel" may originate from

8201-420: Is the static ACDA, the constant g {\displaystyle g} is the acceleration of gravity , and interval t p r t {\displaystyle t_{prt}} is the perception-reaction time —usually between 1.0 and 2.5 seconds. See Table of safe speed versus forward line-of-sight The second case describes the relationship of horizontal sight distance on safe speed. It

8340-416: Is well known that people instead resolve such challenges by attribute substitution , which in this case can mean simply emulating the behaviors of others. In accord with the cultural theory of risk , indeed a substantial part of a driver's risk perception comes from comparing their contemplated conduct to the behavior of others; this includes the safeness of a given speed, notwithstanding the actual risk. As

8479-550: The Old French word travail , which means 'work'. According to the Merriam-Webster dictionary, the first known use of the word travel was in the 14th century. It also states that the word comes from Middle English travailen , travelen (which means to torment, labor, strive, journey) and earlier from Old French travailler (which means to work strenuously, toil). In English, people still occasionally use

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8618-518: The Seconds of Distance to Stop Rule . The ACDA distances are a principal component to be evaluated in the determination of the maximum safe speed (V BSL ) under the basic speed law, without which the maximum safe speed cannot be determined. As mathematical statements are more precise than verbal statements alone, the relation of the ACDA as a subset of the basic speed rule for land based vehicles may be objectively quantified as follows: The value of

8757-565: The U.S. Department of Agriculture 's natural resources inventory , urban areas are officially known as developed areas or urban and built-up areas. Such areas include cities, ethnic villages, other built-up areas of more than 10 ac (4 ha), industrial sites, railroad yards, cemeteries, airports, golf courses, shooting ranges, institutional and public administration sites, and similar areas. The 1997 national resources inventory placed over 98,000,000 ac (40,000,000 ha) in this category, an increase of 25,000,000 ac (10,000,000 ha) since 1982. Argentina

8896-469: The calculus of negligence because speed is an inherent factor in vehicular accidents which are a leading cause of priceless life loss and lawsuits, and the burden of a precautions speed is radically lower than the former. The assumption of risk resulting from the unsafe activity of driving faster than one can stop within one's vision, does not depend ex post facto on what you happened to hit, for which by nature you could not have known; it could have been

9035-489: The inferred design speed . In some cases, police focused on driving while "influenced", pull over slower quartile sober night-time drivers moving no faster than they can stop within the radius of their headlights; this discourages adjusting speed downward from anything but the posted "maximum speed" permitted by law—which is determined as previously described. It is often unsafe or illegal to drive in excess of 40–50 mph at night. A general principle in liability doctrine

9174-471: The maximum posted speed limit at night, often in violation of the ACDA rule and this shows up in accident data. As a corollary to the rule that drivers generally must not pose an "immediate hazard" upon where or when they cannot assure such distance ahead is clear, it follows that others may presume that no vehicle is posing an "immediate hazard" from beyond where they can see with proper lookout. Where there are cross roads or side roads with view obstructions,

9313-428: The urban revolution of the 4th millennium BCE led to the formation of human civilization and ultimately to modern urban planning , which along with other human activities such as exploitation of natural resources has led to a human impact on the environment . In 1950, 764 million people or about 30 percent of the world's 2.5 billion people lived in urban areas. By 2014, it was 3.9 billion or about 53 percent of

9452-499: The visual angle illusion may also play a role. Vehicles that are approaching an intersection from beyond the SAVT limit cannot be reliably distinguished between moving or parked, though they may be traveling at such an imprudent speed as to pose an immediate hazard. In this circumstance, it is impossible for the entering driver to have fair notice that his or her contemplated conduct is forbidden by such hazard, and any legal expectation to

9591-511: The 20th century, notably after the Second World War where there was a surplus of both aircraft and pilots. Air travel has become so ubiquitous in the 21st century that one woman, Alexis Alford , visited all 196 countries before the age of 21. Travel may be local, regional, national (domestic) or international. In some countries, non-local internal travel may require an internal passport , while international travel typically requires

9730-612: The ACDA duty of which instills the necessary room to survive uninjured from such foreseeable and excusable error while adding redundancy in the responsibility to avoid a collision; mere unilateral duties laid down to assure the safety of others tend to result in hazardous risk compensation by those unfettered parties resulting in a moral hazard . Allowing one to drive faster than their vision permits them to safely stop, results in there being no core standard of care regarding safe speed making unsafe speed laws void for vagueness . The ACDA minimum standard gives fair notice of what conduct

9869-507: The ACDA is extended beyond line of sight, by explicitly designating this law change to certain marked high functional classification roadways having meet strict engineering criteria. The ACDA rule is analogous to aviation visual flight rules , and its discussed exception—allowed only in a well regulated control zone—is analogous to instrument flight rules . Unlike both visual and instrumental flight rules, where federal and international administrative law applies seamlessly and uniformly across

10008-628: The ACDA rule as required care or safe practice. Explicit ACDA statutes and regulations, especially those of which create a citable driving or maritime offense, are aimed at preventing harm that could result from potentially negligent behavior—whereas the slightly more obscure common law ACDA doctrine is most easily invoked to remedy actual damages that have already occurred as a result of such negligence. Unsafe speed statutes are immune from being void for vagueness when they contain explicit ACDA clauses. Explicit and implicit ACDA rules govern millions of North American drivers. Not all jurisdictions have applied

10147-513: The ACDA rule is that technology, expectations, and desires may modernize, but the laws of physics can not and do not. The deceleration coefficients and reactions times may change from conveyance by chariot , horse and buggy , internal combustion engine , electric motor , and by driverless car, but the equations governing stopping distances are immutable. Finally, where it is the policy of the law not to fault well intending diligent citizens for innocent mistakes, human life reaps continued benefit from

10286-663: The North American urban area) and its commuter belt ( couronne ). Americans would find the INSEE definition of the urban area to be similar to their metropolitan area . The largest cities in France, in terms of urban area population (2017), are Paris (12,628,266), Lyon (2,323,221), Marseille (1,760,653), Toulouse (1,360,829), Bordeaux (1,247,977), Lille (1,191,117), Nice (1,006,201), Nantes (972,828), Strasbourg (790,087) and Rennes (733,320). Germany has

10425-672: The Northern and Western ones. Urban areas in Sweden ( tätorter ) are statistically defined localities, totally independent of the administrative subdivision of the country. There are 1,956 such localities in Sweden , with a population ranging from 200 to 1,372,000 inhabitants. In 2013 the United Kingdom 's Office for National Statistics (ONS) published 2011 Built-up Areas – Methodology and Guidance which sets out its definition of

10564-617: The Philippine population lived in urban areas. With an estimated population of 16.3 million, Metro Manila is the most populous metropolitan area in the Philippines and the 11th in the world . However, the greater urban area is the 5th largest in the world with a population of 20,654,307 people (2010 estimate). As an island city-state , about 5.6 million people live and work within 700 square kilometres (270 sq mi). With 64 islands and islets , Singapore Island makes up

10703-407: The U.S. are those of Los Angeles , Chicago , Miami , Houston , and Dallas . 80.0 percent of the population of the United States lives within the boundaries of an urban area as of the 2020 census. The concept of Urbanized Areas as defined by the U.S. Census Bureau is often used as a more accurate gauge of the size of a city, since in different cities and states the lines between city borders and

10842-565: The United States in the 1950 census, while urban clusters were added in the 2000 census. The distinction between urbanized areas and urban clusters was removed for the 2020 census. Urban areas consist of a densely-settled urban core, plus surrounding developed areas that meet certain density criteria. Since urban areas are composed of census blocks and not cities, counties, or county-equivalents, urban area boundaries may consist of partial areas of these political units. Urban areas are distinguished from rural areas : any area not part of an urban area

10981-440: The advent of a network of railways in the 19th century. Travel for the purpose of tourism is reported to have started around this time when people began to travel for fun as travel was no longer a hard and challenging task. This was capitalized on by people like Thomas Cook selling tourism packages where trains and hotels were booked together. Airships and airplanes took over much of the role of long-distance surface travel in

11120-424: The assured clear distance terminates at the closest path of potential users of the roadway until there is such a view which assures the intersection will remain clear. In such situations, approach speed must be reduced in preparation for entering or crossing a road or intersection or the unmarked pedestrian crosswalks and bike paths they create because of potential hazards. This jurisprudence arises in-part because of

11259-402: The boundaries of these towns. This distinction may give a misleading impression in some cases, since some localities with only village status may have acquired larger and denser populations than many many smaller towns with most excessive example of Poznań , most spread urban area of the country with population of the city app. 534 thousand and metropolitan area around 1 million inhabitants. On

11398-621: The capital and largest city of Russia , has a population estimated at 12.4 million residents within the city limits, while over 17 million residents in the urban area, and over 20 million residents in the Moscow Metropolitan Area . It is among the world's largest cities , being the most populous city entirely within Europe , the most populous urban area in Europe, the most populous metropolitan area in Europe, and also

11537-486: The concept of the "urban area" used in road safety statistics. This term was first created by Geographer Brian Manning. The last concept is also known as " built-up area in road safety ". According to the definition by the Office for National Statistics , "Built-up areas are defined as land which is 'irreversibly urban in character', meaning that they are characteristic of a town or city. They include areas of built-up land with

11676-416: The conditions along the road. See reference V BSL derivations for basic physics explanation. For the top case, the maximum speed is governed by the assured clear "line-of-sight", as when the "following distance" aft of forward traffic and "steering control" are both adequate. Common examples include when there is no vehicle to be viewed, or when there is a haze or fog that would prevent visualizing

11815-428: The conditions. The speeds at which most people drive can only be a very rough guide to safe speed, and an illegal or negligent custom or practice is not in itself excusable. Safe speed approximates the inferred design speed adjusted for environmental alterations and vehicle and person specific factors when V ACDA s is the limiting factor. The Solomon curve concept can create an approach-avoidance conflict within

11954-481: The contrary would implicate violating the vagueness doctrine of the US Constitution . It is the duty of the through-driver to decelerate and apply the ACDA principle specifically to the intersection. See Table of detection thresholds . When approaching an un-signalized intersection controlled by a stop sign , the assured clear distance ahead is: Normal acceleration " a i " for a passenger vehicle from

12093-481: The criminal blood alcohol threshold below levels for which the risk is statistically marginal, the tolerance for speeding—of which each speed unit increment carries an equatable risk relative to BAC—remains relatively neglected. Speed is responsible for more crashes and economic loss than is alcohol. The discrepancy may be partly explained by powerful special interest groups that are lobbying against drunk driving and for loser speed regulation. Travel Travel

12232-404: The degree of urbanization of a population. The first, urban population, describes the percentage of the total population living in urban areas, as defined by the country. The second measure, rate of urbanization, describes the projected average rate of change of the size of the urban population over the given period of time. According to Urbanization by sovereign state article, the world as a whole

12371-715: The destination. Travel to Mount Everest , the Amazon rainforest , extreme tourism , and adventure travel are more difficult forms of travel. Travel can also be more difficult depending on the method of travel, such as by bus , cruise ship , or even by bullock cart . Reasons for traveling include recreation , holidays, rejuvenation, tourism or vacationing , research travel, the gathering of information, visiting people, volunteer travel for charity , migration to begin life somewhere else, religious pilgrimages and mission trips , business travel , trade , commuting , obtaining health care, waging or fleeing war , for

12510-507: The details. By the late 1920s, the term "assured clear distance ahead" came into widespread use as the identity of a standard of care element in choosing safe speed, with differing jurisdictions adopting the language to carry its same effects. Much of the earliest published record naturally pertains to high stakes wrecks among vessels or vehicles as defined in those times, though the obvious principle applies to chariots and might in fact be time immemorial . Horses may still be expected to use

12649-426: The distance between each building has to be of less than 50 m, although exceptions are made due to parks, industrial areas, rivers, and similar. Groups of houses less than 400 m from the main body of an urban area are included in the urban area. In Poland , official "urban" population figures simply refer to those localities which have the status of towns ( miasta ). The "rural" population is that of all areas outside

12788-458: The distance to remain clear beyond line of sight would ultimately be transferred to its taxpayers. This only generally occurs when governments have been tasked by constituents or their courts to take the responsibly to design and maintain roadways that "assure" the distance will be clear beyond the proximate edge of clear visibility. Pressures to make such changes may arise from cultural normalization of deviance and unnecessary risk, misunderstanding

12927-430: The driver could clearly and immediately know when he or she may or may not take such extended "assurance". Few roads might meet these requirements except some of the highest functional classification controlled-access highways such as freeways and autobahns . Even if such criteria are met, the law must also exempt driver liability for maintaining clear distance ahead. In most democracies, such liability for failures of

13066-414: The driver who wishes neither to drive faster than is lawful and the conditions allow nor have an unsafe speed discrepancy between other vehicles on the road; it is never legal to go faster than the speed limit, and unilaterally reducing the risk of the latter can lead to a mass crash caused by the former. Many people are challenged by the concept of unsafe speed because they find it vague and arbitrary. It

13205-686: The enjoyment of traveling, or other reasons. Travelers may use human-powered transport such as walking or bicycling ; or vehicles , such as public transport , automobiles , trains , ferries , boats , cruise ships and airplanes . Motives for travel include: Travel dates back to antiquity where wealthy Greeks and Romans would travel for leisure to their summer homes and villas in cities such as Pompeii and Baiae . While early travel tended to be slower, more dangerous, and more dominated by trade and migration, cultural and technological advances over many years have tended to mean that travel has become easier and more accessible. Humankind has come

13344-563: The extent of irreversible urban development indicated on Ordnance Survey maps. The definition is an extent of at least 20 ha and at least 1,500 census residents. Separate areas are linked if less than 200 m (220 yd) apart. Included are transportation features. The UK has five Urban Areas with a population over a million and a further sixty nine with a population over one hundred thousand . The Australian Bureau of Statistics refers to urban areas as Urban Centres, which it generally defines as population clusters of 1,000 or more people. Australia

13483-488: The genesis of most legal doctrine governing problems which precede a legislative solution, the ACDA principle generally originates to decisional precedent by high courts which reasoned general common sense rules of conduct of which naturally follow from the repetitive process of determining specific culpability. Legislation often subsequently followed which either superfluously codified and endorsed or revised these principles, of which courts would in turn continue to flesh out

13622-403: The globe, a global definition is not possible. European countries define urbanized areas on the basis of urban-type land use , not allowing any gaps of typically more than 200 metres (220 yd), and use satellite imagery instead of census blocks to determine the boundaries of the urban area. In less-developed countries , in addition to land use and density requirements, a requirement that

13761-443: The horizontal sight distance in time to collide, however this says nothing of whether the vehicle can stop by the end of this type of assured clear distance. Equating this distance to the total stopping distance and solving for speed yields one's maximum safe speed as purely dictated by the horizontal sight distance. The ACDA may also be dynamic as to the moving distance past which a motorist can be assured to be able to stay clear of

13900-404: The horizontal sight distance, at times obscuring wildlife which may be spooked by an approaching vehicle and run across the road to escape with their herd . This principle also applies to approaching vehicles and pedestrians at uncontrolled intersections and to a lesser degree by un-signalized intersections controlled by a yield sign . Horizontal sight distance " d hsd " affects the ACDA because

14039-416: The judiciary has explicitly established the state's ACDA law include Indiana, Iowa, Kansas, Louisiana, Michigan, New York, North Carolina, Ohio, Tennessee, Vermont, Wisconsin, and California. Many states have further passed statutes which require their courts to more inflexibly weigh the ACDA in their determination of reasonable speed or behavior. Such statutes do so in part by designating ACDA violations as

14178-516: The known difficulty in estimating the distance and velocity of an approaching vehicle, which is psychophysically explained by its small angular size and belated divergence from an asymptotically null rate of expansion, which is beyond the subtended angular velocity detection threshold (SAVT) limits of visual acuity by way of the Stevens' power law and Weber–Fechner law , until the vehicle may be dangerously close; subjective constancy and

14317-494: The land area is counted. The Randstad is the country's largest conurbation located in the west of the country and contains the four largest cities: Amsterdam, Rotterdam , The Hague , and Utrecht . The Randstad has a population of 7 million inhabitants and is the 6th largest metropolitan area in Europe. Norway defines urban areas ("tettsteder") similarly to the other Nordic countries . Unlike in Denmark and Sweden,

14456-525: The largest city by land area on the European continent. Saint Petersburg , the cultural capital, is the second-largest city, with a population of roughly 5.4 million inhabitants. Other major urban areas are Yekaterinburg , Novosibirsk , Kazan , Nizhny Novgorod , and Chelyabinsk . Spain is a very highly urbanized country. Madrid is its largest urban area. The Southern and Eastern coasts with Barcelona , Valencia and Málaga are more urbanised than

14595-617: The largest urban area in the country. According to the United Nations Economic and Social Commission for Asia and the Pacific , the country has the highest urbanised population in Southeast Asia, with 100 percent of its population living in an urban area. The Urban Redevelopment Authority (URA) is responsible for the urban land-use planning, which designates land use and urban density of the country. The country

14734-658: The late 16th century, it became fashionable for young European aristocrats and wealthy upper-class men to travel to significant European cities as part of their education in the arts and literature. This was known as the Grand Tour , and included cities such as London, Paris, Venice, Florence, and Rome. However, the French Revolution brought with it the end of the Grand Tour. Travel by water often provided more comfort and speed than land-travel, at least until

14873-401: The law needs to be clear, precise, and uniform at a national level for the panoply of automobile manufacturers with the strict liability for their programming of law-abiding self-driving vehicles. It is foreseeable that two self-driving car makes can collide because their algorithm of the law letter is different; a resolvable issue that has been troubling human drivers for decades. The ACDA is

15012-460: The law. During times of darkness, commercial vehicles can see ahead about 250 feet with low beams, and about 350–500 feet with high beams. This clear distance corresponds to a maximum safe speed of 52 mph and 65-81 mph respectively on dry pavement with good tires, which is attenuated further by convex and lateral road curvature ; safe speed is always dynamic. Non-commercial vehicles have even shorter lighting distances. Drivers commonly drive

15151-422: The major cities, returning home to the countryside periodically with their earnings. China has more cities with one million or more long-term residents than any other country, including the three global cities of Beijing , Hong Kong, and Shanghai ; by 2025, the country will be home to 221 cities with over a million inhabitants. The figures in the table below are from the 2008 census, and are only estimates of

15290-513: The majority of the world's population lived in a city. By that time a high estimate calculated up to 3.5 million square kilometers of land were urban, estimates ranging from 1% of global land area. In 2014 there were 7.3 billion people living on the planet, of which the global urban population comprised 3.9 billion. The Population Division of the United Nations Department of Economic and Social Affairs at that time predicted

15429-437: The maximum safe speed from real-time mathematical calculations of sight distances and stopping distances for their particular vehicle. Motor vehicle operators of average intelligence are constantly required to utilize their kinesthetic memory in all sorts of driving tasks including every time they brake to a full stop at a stop line in a panoply of conditions. Like throwing a softball, one does not have to mathematically calculate

15568-543: The most urbanised nation in South Asia. Furthermore, 50% of Pakistanis live in towns of 5,000 people or more. Karachi is the most populated city in Pakistan closely followed by Lahore according to the 2017 Census . In Bangladesh , there are total 532 urban areas, which are divided into three categories. Those are City Corporation , Municipal Corporation (Pourasova) and Upazila town . Among those urban areas, Dhaka

15707-419: The nearest object, tree trunk or shrub foliage mass face, plant setback, or mature growth. Horizontal sight distance is not to be confused with the clear recovery zone which provides hazardous vegetation set-back to allow errant vehicles to regain control, and is exclusive to a mowed and limbed-up forest which can allow adequate sight distance, but unsafe recovery. The height and lateral distance of plants restrict

15846-437: The new term " population centre "; the new term was chosen in order to better reflect the fact that urban vs. rural is not a strict division, but rather a continuum within which several distinct settlement patterns may exist. For example, a community may fit a strictly statistical definition of an urban area, but may not be commonly thought of as "urban" because it has a smaller population, or functions socially and economically as

15985-447: The original common law driving rule preceding statutized traffic law , it is an ever important foundational rule in today's complex driving environment. Because there are now protected classes of roadway users—such as a school bus , mail carrier , emergency vehicle , horse-drawn vehicle , agricultural machinery , street sweeper , disabled vehicle , cyclist , and pedestrian —as well as natural hazards which may occupy or obstruct

16124-530: The other hand, the Katowice urban area with numerous large and medium cities covers 1,468 km and has above 2 million people. The metropolitan areas in Poland are the biggest urban zones (e.g. Katowice metropolitan area , Łódź metropolitan area and Szczecin metropolitan area ) and have great impact on the rural surroundings, as it is around Lublin , Radom , Kielce , Tarnów and Białystok . Moscow ,

16263-693: The proximate edge of clear visibility and choose such a speed accordingly, transfers classic common law liability from that driver for his or her "blind" actions. This duty to assure clear distance ahead is inevitably transferred, as an externality to everybody or thing else who must instead warn the driver, such as the government, its road engineers, and maintainers. As it is generally probable and foreseeable that, chance will permit, and at some point there will be an obstruction beyond some driver's line of sight, such an entitlement challenges centuries of precedent in negligence doctrine in addition to posing difficult policy and engineering challenges. It also violates

16402-438: The purpose of the road functional classification system, underestimation of increased risk, and reclamation of commute time. One of the greatest difficulties created by such an extension of the ACDA is the frequency at which roads reduce their functional classification unbeknownst to drivers who continue unaware they have lost this extended "assurance" or do not understand the difference. Such nuance in applicable jurisdictions

16541-465: The range of his vision. In numerous jurisdictions, this rule has been incorporated in statutes which typically require that no person shall drive any motor vehicle in and upon any public road or highway at a greater speed than will permit him to bring it to a stop within the assured clear distance ahead." Decisional law usually settles the circumstances by which a portion of the roadway is assuredly clear without it being mentioned in statute. States where

16680-408: The road, were it not for their decisions to drive faster than dictated by the assured clear distance ahead. Regardless of what behavior an authority might encourage by fabricating new rights, it remains timeless that constituents cannot sue the wind for causing a wreck when it inevitably violates a "modern right to drive faster than permitted by the ACDA" by failing to warn them it knocked down a tree in

16819-503: The roadway beyond the edge of visibility, negligence may not depend ex post facto on what a driver happened to hit, could not have known, but had a concurrent duty to avoid. Furthermore, modern knowledge of human factors has revealed physiological limitations—such as the subtended angular velocity detection threshold (SAVT)—which may make it difficult, and in some circumstance impossible, for other drivers to always comply with right-of-way statutes by staying clear of roadway. As with

16958-399: The roadways, as well bicycles and automobiles. The former are a regular appearance in both urban areas and in the country , and are commonly exercised by commuters and Amish . Many roads are unchanged since the 1800s while controlled-access highways have been invented specifically for the automobile. "At common law a motorist is required to regulate his speed so that he can stop within

17097-476: The rule uniformly, most often differing over exceptions for specific "sudden emergencies". There has been an increased interest in the ACDA codified as a universal standard of care that has been brought about by recent technological and social changes such as event data recorders , dashcams , self-driving cars , safe cities and multi-use movements, and a movement to reduce claims by speeders against governments for "dangerous conditions" when operating speeds exceed

17236-436: The services of many itinerant peddlers wandering from village to hamlet, gyrovagues (wandering monks) and wandering friars brought theology and pastoral support to neglected areas, traveling minstrels toured, and armies ranged far and wide in various crusades and in sundry other wars. Pilgrimages were common in both the European and Islamic world and involved streams of travelers both locally and internationally. In

17375-423: The states, the ACDA rule governing ground transportation is relatively variegated across states and judicial circuits . Primitive patchwork governance over a prominent interstate commercial subject , in a modern era where citizens quickly and more frequently travel father than ever before, creates problems for modern driverless cars which are programmed, distributed, sold, and traded at national levels. As opposed to

17514-500: The target of a crime, leaving copies of one's passport and itinerary information with trusted people, obtaining medical insurance valid in the country being visited and registering with one's national embassy when arriving in a foreign country. Many countries do not recognize drivers' licenses from other countries; however most countries accept international driving permits . Automobile insurance policies issued in one's own country are often invalid in foreign countries, and it

17653-441: The tightest radius of highway onramps. The principle of critical speed is often applied to the problem of traffic calming , where curvature is both used to govern maximum road speed, and used in traffic circles as a device to force drivers to obey their duty to slow down when approaching an intersection. See Table of curvatures and critical speeds The bottom case is invoked when the maximum velocity for surface control V cl

17792-471: The time t i = ⁠ d hsd / V i ⁠ it takes for an intercepting object, animal, pedestrian, or vehicle with speed " V i " to transverse this distance after emerging from the proximate edge of lateral visibility affords a vehicle with speed " V " a clear distance of " V*t i ". Thus, the assured clear intercept distance " ACDA si " is: The faster one drives, the farther down-road an interceptor must be in order to be able to transverse

17931-571: The time of independence and has several different causes. The majority of southern Pakistan's population lives along the Indus River . Karachi is its most populous city. In the northern half of the country, most of the population lives in an arc formed by the cities of Lahore , Faisalabad , Rawalpindi , Islamabad , Gujranwala , Sialkot , Gujrat , Jhelum , Sargodha , Sheikhupura , Nowshera , Mardan and Peshawar . During 1990–2008, city dwellers made up 36% of Pakistan's population, making it

18070-425: The time of which they do not agree, it is often simply a jurisdiction's failure in their law to sufficiently quantify and disseminate fair notice of an explicit standard of care, such as the ACDA rule. Most DMV driver manuals teach the practice, but far fewer states explicitly back it up in their actual statutes and law enforcement. If drivers were mindful of the ACDA, the operating speed would by definition not exceed

18209-470: The urban population would occupy 68% of the world population by 2050, with 90% of that growth coming from Africa and Asia. Urban areas are created and further developed by the process of urbanization. They are measured for various purposes, including analyzing population density and urban sprawl . Urban areas are also mostly found in the United States , Canada , Brazil , Mexico , Argentina , Chile , Japan and Australia and many other countries where

18348-492: The urban populations within administrative city limits; a different ranking exists when considering the total municipal populations (which includes suburban and rural populations). The large " floating populations " of migrant workers make conducting censuses in urban areas difficult; the figures below include only long-term residents. In Japan , urbanized areas are defined as contiguous areas of densely inhabited districts (DIDs) using census enumeration districts as units with

18487-435: The urbanization rate is over 80%. Unlike an urban area, a metropolitan area includes not only the urban area, but also satellite cities plus intervening rural land that is socio-economically connected to the urban core city, typically by employment ties through commuting , with the urban core city being the primary labor market. The concept of an "urban area" as used in economic statistics should not be confused with

18626-474: The urbanized area of that city are often not the same. For example, the city of Greenville, South Carolina has a city population just over 68,000 and an urbanized area population of around 400,000, while Greensboro, North Carolina has a city population just over 285,000 and an urbanized area population of around 300,000 — meaning that Greenville is actually "larger" for some intents and purposes, but not for others, such as taxation, local elections, etc. In

18765-450: The utility of the law by making it arbitrarily vague . A national uniformity standard which either administratively lays down the ACDA law as has been done for aircraft, or requires states to legislatively enact in order to receive federal DOT funding as has been done for the national legal drinking age, is a subject of debate for those who argue far more people die in cars than in aircraft. While group polarization towards safety has shifted

18904-522: The variable "e" is the sine of the angle of inclination of the road's slope . For a level road this value is zero, and for small angles it approximates the road's percent grade divided by one hundred. The maximum velocity permitted by the Assured Clear Distance Ahead is controlling of safe speed (V BSL ) for only the top and two cases. Safe speed may be greater or less than the actual legal speed limit depending upon

19043-675: The vehicle may not slide until it experiences 0.8g. Speed wobble , hydroplaning , roll center , fishtailing , jackknife tendencies, potholes , washboarding , frost heaving , and tire speed rating are other factors limiting V cl . Safe speed is the maximum speed permitted by the basic speed law and negligence doctrine. Safe speed is not the same as the 85 percentile operating speed used by traffic engineers in establishing speed zones. Fog, snow, or ice can create conditions where most people drive too fast, and chain reaction accidents in such conditions are examples of where large groups of drivers collided because they failed to reduce speed for

19182-496: The words travail , which means struggle. According to Simon Winchester in his book The Best Travelers' Tales (2004) , the words travel and travail both share an even more ancient root: a Roman instrument of torture called the tripalium (in Latin it means "three stakes", as in to impale). This link may reflect the extreme difficulty of travel in ancient times. Travel in modern times may or may not be much easier, depending upon

19321-401: The world's 7.3 billion people that lived in urban areas. The change was driven by a combination of increased total population and increased percent of population living in urban areas. In 2009, the number of people living in urban areas (3.42 billion) surpassed the number living in rural areas (3.41 billion), and since then the world has become more urban than rural. This was the first time that

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