Details for Benchmark: JW1712
N 39° 41.617 W 079° 10.267 (NAD 83)
Coordinates may not be exact. Altitude is ADJUSTED and location is SCALED. (more info)
- In GARRETT county, MD View Original Datasheet
- SHA 218
- Marker Type:
- survey disk
- abutments and piers of large bridges
- Probably hold position/elevation well.
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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 4.1 MI (6.6 KM) EAST OF KEYSERS RIDGE, 0.9 MI (1.4 KM) WEST-SOUTHWEST OF GRANTSVILLE, AND 9.1 MI (14.6 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 0.65 MI (1.05 KM) TO THE MARKER ON THE LEFT. THE POINT IS MARKED WITH A MARYLAND STATE HIGHWAY ADMINISTRATION SURVEY DISK, CEMENTED IN A DRILL HOLE ON THE SOUTH END OF A BACKWALL WHICH IS PART OF THE WEST ABUTMENT OF A BRIDGE NUMBERED 11050 WHERE THE EASTBOUND LANE OF INTERSTATE HIGHWAY 68 CROSSES OVER SHADE HOLLOW ROAD. IT IS 0.7 FT (21.3 CM) WEST OF THE MOST WEST BRIDGE EXPANSION JOINT, 2.0 FT (0.6 M) NORTHEAST OF THE NORTH EDGE OF THE SOUTH BRIDGE PARAPET WALL, 9.5 FT (2.9 M) SOUTHEAST OF THE NORTHWEST END OF THE SOUTH BRIDGE PARAPET WALL 19.5 FT (5.9 M) SOUTHWEST FROM THE CENTER OF THE EASTBOUND LANE OF INTERSTATE HIGHWAY 68, AND 20.9 FT (6.4 M) SOUTHEAST FROM THE CENTER OF A DROP INLET. IT IS ABOUT THE SAME ELEVATION AS 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.