<P> There are runway markings and signs on most large runways . Larger runways have a distance remaining sign (black box with white numbers). This sign uses a single number to indicate the remaining distance of the runway in thousands of feet . For example, a 7 will indicate 7,000 ft (2,134 m) remaining . The runway threshold is marked by a line of green lights . </P> <P> There are three types of runways: </P> <Ul> <Li> Visual runways are used at small airstrips and are usually just a strip of grass, gravel, ice, asphalt, or concrete . Although there are usually no markings on a visual runway, they may have threshold markings, designators, and centerlines . Additionally, they do not provide an instrument - based landing procedure; pilots must be able to see the runway to use it . Also, radio communication may not be available and pilots must be self - reliant . </Li> <Li> Non-precision instrument runways are often used at small - to medium - size airports . These runways, depending on the surface, may be marked with threshold markings, designators, centerlines, and sometimes a 1,000 ft (305 m) mark (known as an aiming point, sometimes installed at 1,500 ft (457 m)). They provide horizontal position guidance to planes on instrument approach via Non-directional beacon, VHF omnidirectional range, Global Positioning System, etc . </Li> <Li> Precision instrument runways, which are found at medium - and large - size airports, consist of a blast pad / stopway (optional, for airports handling jets), threshold, designator, centerline, aiming point, and 500 ft (152 m), 1,000 ft (305 m) / 1,500 ft (457 m), 2,000 ft (610 m), 2,500 ft (762 m), and 3,000 ft (914 m) touchdown zone marks . Precision runways provide both horizontal and vertical guidance for instrument approaches . </Li> </Ul> <Li> Visual runways are used at small airstrips and are usually just a strip of grass, gravel, ice, asphalt, or concrete . Although there are usually no markings on a visual runway, they may have threshold markings, designators, and centerlines . Additionally, they do not provide an instrument - based landing procedure; pilots must be able to see the runway to use it . Also, radio communication may not be available and pilots must be self - reliant . </Li>

How long are the 1000 foot markers on a runway
find me the text answering this question