Details for Benchmark: JW1713
N 39° 41.633 W 079° 10.417 (NAD 83)
Coordinates may not be exact. Altitude is ADJUSTED and location is SCALED. (more info)
- In GARRETT county, MD View Original Datasheet
- SHA 219
- Marker Type:
- survey disk
- mat foundation, concrete slab, etc.
- May hold, but of type commonly subject to surface motion.
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Documented History (by the NGS)
|01/01/1992 by MDSHA (MONUMENTED)
|DESCRIBED BY MARYLAND DOT HIGHWAY ADMINISTRATION 1992
THE MARKER IS LOCATED ABOUT 4.0 MI (6.4 KM) EAST OF KEYSERS RIDGE, 1.0 MI (1.6 KM) WEST OF GRANTSVILLE, AND 9.0 MI (14.5 KM) EAST-NORTHEAST OF ACCIDENT. IT IS LOCATED ON INTERSTATE HIGHWAY 68 RIGHT-OF-WAY. TO REACH FROM A POINT WHERE STATE HIGHWAY 495 CROSSES OVER INTERSTATE HIGHWAY 68 NEAR GRANTSVILLE, GO WEST ON INTERSTATE HIGHWAY 68 FOR 0.75 MI (1.21 KM) TO THE MARKER ON THE LEFT. THE POINT IS MARKED WITH A 2.5 INCH MARYLAND STATE HIGHWAY ADMINISTRATION SURVEY DISK, CEMENTED IN A DRILL HOLE IN THE NORTH SIDE OF THE MOST NORTHERLY ONE OF TWO 2.0 FT. ROUND CONCRETE BASE FOR A LARGE HIGHWAY SIGN. IT IS 3.7 FT (1.1 M) SOUTHWEST OF A METAL GUARDRAIL, 28.4 FT (8.7 M) SOUTHWEST OF THE CENTER OF THE EASTBOUND LANE OF INTERSTATE HIGHWAY 68, AND JUST SOUTH OF A PAVED CROSSOVER IN THE MEDIAN STRIP OF THE HIGHWAY. IT IS ABOUT 2.0 FT (0.6 M) LOWER THAN THE SURFACE OF THE HIGHWAY.
- The horizontal coordinates were scaled from a topographic map and have an estimated accuracy of +/- 6 seconds.
- The orthometric height was determined by differential leveling and adjusted by the National Geodetic Survey in April 1995.
- The geoid height was determined by GEOID99.
- The dynamic height is computed by dividing the NAVD 88 geopotential number by the normal gravity value computed on the Geodetic Reference System of 1980 (GRS 80) ellipsoid at 45 degrees latitude (g = 980.6199 gals.).
- The modeled gravity was interpolated from observed gravity values.