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Interstate Standards
Standards for Interstate Highways in the United States are defined by the American Association of State Highway and Transportation Officials (AASHTO) in the publication ''A Policy on Design Standards: Interstate System''. For a certain highway to be considered an Interstate Highway, it must meet these construction requirements or obtain a waiver from the Federal Highway Administration. Standards Standardization helps keep road design consistent, such that drivers can learn the consistent features and drive accordingly. Standardization can therefore decrease accidents and increase driver safety. These standards are, : * Controlled access: All access onto and off the highway is to be controlled with interchanges and grade separations, including all railroad crossings. Interchanges are to provide access to and from both directions of the highway and both directions of the crossroad. Interchanges should be spaced at least apart in urban areas and apart in rural areas; coll ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
American Association Of State Highway And Transportation Officials
The American Association of State Highway and Transportation Officials (AASHTO) is a standards setting body which publishes specifications, test quality control, protocols, and guidelines that are used in highway design and construction throughout the United States. Despite its name, the association represents not only highways but air, rail, water, and public transportation as well. Although AASHTO sets transportation standards and policy for the United States as a whole, AASHTO is not an agency of the federal government; rather it is an organization of the states themselves. Policies of AASHTO are not federal laws or policies, but rather are ways to coordinate state laws and policies in the field of transportation. Purpose The American Association of State Highway Officials (AASHO) was founded on December 12, 1914. Its name was changed to American Association of State Highway and Transportation Officials on November 13, 1973. The name change reflects a broadened scope to co ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sight Distance
Stopping sight distance is one of several types of sight distance used in road design. It is a near worst-case distance a vehicle driver needs to be able to see in order to have room to stop before colliding with something in the roadway, such as a pedestrian in a crosswalk, a stopped vehicle, or road debris. Insufficient sight distance can adversely affect the safety or operations of a roadway or intersection. Stopping sight distance is the distance traveled during the two phases of stopping a vehicle: perception-reaction time (PRT), and maneuver time (MT).American Association of State Highway and Transportation Officials (1994) ''A Policy on Geometric Design of Highways and Streets'' (pp. 117–118) Perception-reaction time is the time it takes for a road user to realize that a reaction is needed due to a road condition, decide what maneuver is appropriate (in this case, stopping the vehicle), and start the maneuver (taking the foot off the accelerator and depressing the br ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rainfall
Rain is water droplets that have condensed from atmospheric water vapor and then fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides water for hydroelectric power plants, crop irrigation, and suitable conditions for many types of ecosystems. The major cause of rain production is moisture moving along three-dimensional zones of temperature and moisture contrasts known as weather fronts. If enough moisture and upward motion is present, precipitation falls from convective clouds (those with strong upward vertical motion) such as cumulonimbus (thunder clouds) which can organize into narrow rainbands. In mountainous areas, heavy precipitation is possible where upslope flow is maximized within windward sides of the terrain at elevation which forces moist air to condense and fall out as rainfall along the sides of mountains. On the leeward side of mountains, desert climates can exi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Drainage
Drainage is the natural or artificial removal of a surface's water and sub-surface water from an area with excess of water. The internal drainage of most agricultural soils is good enough to prevent severe waterlogging (anaerobic conditions that harm root growth), but many soils need artificial drainage to improve production or to manage water supplies. History Early history The Indus Valley civilization had sewerage and drainage systems. All houses in the major cities of Harappa and Mohenjo-daro had access to water and drainage facilities. Waste water was directed to covered gravity sewers, which lined the major streets. 18th and 19th century The invention of hollow-pipe drainage is credited to Sir Hugh Dalrymple, who died in 1753. Current practices Geotextiles New storm water drainage systems incorporate geotextile filters that retain and prevent fine grains of soil from passing into and clogging the drain. Geotextiles are synthetic textile fabrics specially ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cross Slope
Cross slope, cross fall or camber is a geometric feature of pavement surfaces: the transverse slope with respect to the horizon. It is a very important safety factor. Cross slope is provided to provide a drainage gradient so that water will run off the surface to a drainage system such as a street gutter or ditch. Inadequate cross slope will contribute to aquaplaning. On straight sections of normal two-lane roads, the pavement cross section is usually highest in the center and drains to both sides. In horizontal curves, the cross slope is banked into superelevation to reduce steering effort and lateral force required to go around the curve. All water drains to the inside of the curve. If the cross slope magnitude oscillates within , the body and payload of high (heavy) vehicles will experience high roll vibration. Cross slope is usually expressed as a percentage: :\text = \frac \times 100\%. Cross slope is the angle around a vertical axis between: * the horizontal line that is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Directional Design Hour Volume
Direction may refer to: *Relative direction, for instance left, right, forward, backwards, up, and down ** Anatomical terms of location for those used in anatomy ** List of ship directions * Cardinal direction Mathematics and science * Direction vector, a unit vector that defines a direction in multidimensional space * Direction of a subspace of a Euclidean or affine space * Directed set, in order theory * Directed graph, in graph theory * Directionality (molecular biology), the orientation of a nucleic acid Music * For the guidance and cueing of a group of musicians during performance, see conducting * ''Direction'' (album) a 2007 album by The Starting Line * Direction (record label), a record label in the UK in the late 1960s, a subsidiary of CBS Records, specialising in soul music * '' Directions: The Plans Video Album'', a DVD video album made of videos inspired by songs from indie rock/pop band Death Cab for Cutie's album ''Plans'' * ''Directions'' (Miles Davis album ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Shoulder (highway)
A shoulder, hard shoulder (British) or breakdown lane, is an emergency stopping lane by the road verge, verge of a road or motorway, on the right side in countries which List of countries with right-hand traffic, drive on the right, and on the left side in countries which List of countries with left-hand traffic, drive on the left. Many wider (U.S.) freeways, or Limited-access road, expressways elsewhere have shoulders on both sides of each directional carriageway — in the median, as well as at the outer edges of the road, for additional safety. Shoulders are not intended for use by through traffic, although there are exceptions. Purpose Shoulders have multiple uses, including: * Emergency vehicles such as ambulances, fire trucks and police cars may use the shoulder to bypass traffic congestion. * In the event of an emergency or Breakdown (vehicle), breakdown, a motorist can pull into the shoulder to get out of the flow of traffic and obtain a greater degree of safety. * Active t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Runaway Truck Ramp
A runaway truck ramp, runaway truck lane, escape lane, emergency escape ramp, or truck arrester bed is a traffic device that enables vehicles which are having braking problems to safely stop. It is typically a long, sand- or gravel-filled lane connected to a steep downhill grade section of a main road, and is designed to accommodate large trucks or buses. It allows a moving vehicle's kinetic energy to be dissipated gradually in a controlled and relatively harmless way, helping the operator stop it safely. Design Emergency escape ramps are usually located in mountainous areas which cause high construction costs and present difficult site selection. A ramp may cost US$1 million. Designs include: *''Arrester bed'': a gravel-filled ramp adjacent to the road that uses rolling resistance to stop the vehicle. The required length of the bed depends on the mass and speed of the vehicle, the grade of the arrester bed, and the rolling resistance provided by the gravel. *''Gravity escape ra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Climbing Lane
Climbing lanes or crawler lanes are a roadway lane design. They allow slower travel for large vehicles, such as large trucks or semi-trailer trucks, ascending a steep grade. Since climbing uphill is difficult for these vehicles, they can travel in the climbing lane without slowing traffic. Description Climbing lanes are a roadway lane design, typically used on major routes such as motorways and interstate highways. In the UK, the climbing lane is also referred to as a crawler lane. They allow slower travel for large vehicles, such as large trucks or semi-trailer trucks, ascending a steep grade. Since climbing uphill is difficult for these vehicles, they can travel in the climbing lane without slowing traffic. Variants A variation that has become common with newer roads and more recent widening schemes is to add an additional "fast" ( passing) lane for the stretch which otherwise would have had a crawler lane. This allows underpowered vehicles to remain in the existing "slow" lane ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Level Of Service (transportation)
Level of service (LOS) is a qualitative measure used to relate the quality of motor vehicle traffic service. LOS is used to analyze roadways and intersections by categorizing traffic flow and assigning quality levels of traffic based on performance measure like vehicle speed, density, congestion, etc. In a more general sense, levels of service can apply to all services in asset management domain. Level-of-Service in the United States of America The following section pertains to only North American highway LOS standards as in the Highway Capacity Manual (HCM) and AASHTO Geometric Design of Highways and Streets ("Green Book"), using letters A through F, with A being the best and F being the worst, similar to academic grading. A: free flow. Traffic flows at or above the posted speed limit and motorists have complete mobility between lanes. The average spacing between vehicles is about 550 ft(167m) or 27 car lengths. Motorists have a high level of physical and psychological com ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lane
In road transport, a lane is part of a roadway that is designated to be used by a single line of vehicles to control and guide drivers and reduce traffic conflicts. Most public roads (highways) have at least two lanes, one for traffic in each direction, separated by lane markings. On multilane roadways and busier two-lane roads, lanes are designated with road surface markings. Major highways often have two multi-lane roadways separated by a median. Some roads and bridges that carry very low volumes of traffic are less than wide, and are only a single lane wide. Vehicles travelling in opposite directions must slow or stop to pass each other. In rural areas, these are often called country lanes. In urban areas, alleys are often only one lane wide. Urban and suburban one lane roads are often designated for one-way traffic. History For much of human history, roads did not need lane markings because most people walked or rode horses at relatively slow speeds. However, when a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Grade (slope)
The grade (also called slope, incline, gradient, mainfall, pitch or rise) of a physical feature, landform or constructed line refers to the tangent of the angle of that surface to the horizontal. It is a special case of the slope, where zero indicates horizontality. A larger number indicates higher or steeper degree of "tilt". Often slope is calculated as a ratio of "rise" to "run", or as a fraction ("rise over run") in which ''run'' is the horizontal distance (not the distance along the slope) and ''rise'' is the vertical distance. Slopes of existing physical features such as canyons and hillsides, stream and river banks and beds are often described as grades, but typically grades are used for human-made surfaces such as roads, landscape grading, roof pitches, railroads, aqueducts, and pedestrian or bicycle routes. The grade may refer to the longitudinal slope or the perpendicular cross slope. Nomenclature There are several ways to express slope: # as an ''angle'' of inc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
